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replacing Mikunis with Amal, BSA lightning #744390
08/04/18 5:51 pm
08/04/18 5:51 pm
Joined: Nov 2013
Posts: 295
Bristol England
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redrooster Offline OP
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Bristol England
Hi all,
Been away for some time but good to be back, need input again.
I intend replacing the Mikuni carbs that came with the a65 with Amals for various reasons but not sure which Amals to order.

The original motor is 1964 and the head has been replaced with a lightning head at some point but I don't know which year the head is from.

I am thinking 930 premiers. Any advice, experience appreciated.


Thanks, the rooster, full of beans

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Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744417
08/04/18 7:32 pm
08/04/18 7:32 pm
Joined: Dec 2017
Posts: 211
England
F
ferretjuggler Offline
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ferretjuggler  Offline
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F

Joined: Dec 2017
Posts: 211
England
BSA never made an A65 in 1964 with twin carbs so basically you have a customised bike anyway.
Originally your bike would have been either an A65 Star or an A65R Rocket, and while the Rocket would be a nice bike to restore to standard, the base model A65 is a little lacklustre (to my tastes anyway) and I'm sure that lots of them mutated into cafe racers as the 1960s progressed.

I'm not actually sure that the AMAL Concentric premier things are actually any good.
The standard Concentric was a good design spoiled by penny pinching, and the premier carbs have changes which are supposed to have addressed all the problems.
Worth a bit of research before parting with your cash ?
I think that the Mikuni VM carbs look terrible on a British bike they just stand out like a sore thumb.
Especially on a twin carb bike with splayed out carbs.
A pity really because apparently the Mikuni VM is a licence built version of an AMAL design.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744435
08/04/18 8:51 pm
08/04/18 8:51 pm
Joined: Aug 2015
Posts: 1,301
Bolton Lancs UK
A
Andy Higham Offline
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Bolton Lancs UK
The Mikuni has several advantages over the AMAL, not all of these were adressed in the premier series
The AMAL is made out of poor material and wears out prematurely
The AMAL manufacturing tolerances are poor
The Mikuni pilot/idle circuit is far superior to that of the AMAL
The Mikuni has a proper cold start system
The Mikuni is spigot mounted giving good heat and vibration insulation
The AMAL flange mount is poorly designed and prone to distortion


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744445
08/04/18 10:37 pm
08/04/18 10:37 pm
Joined: Dec 2017
Posts: 211
England
F
ferretjuggler Offline
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Joined: Dec 2017
Posts: 211
England
I'm not doubting the technical superiority the Mikuni VM, AMAL design or not.
But to my mind they look very wrong on a 1950s or 1960s Brit.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744468
08/05/18 3:56 am
08/05/18 3:56 am
Joined: Jan 2014
Posts: 4,163
Aus
N
NickL Offline
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Aus
If you check out the Burlen site, they will recommend the carb pair for a '69+. they will do the trick.

Andy is right about the carbs but Mikuni's just look crap. I like Dellorto's myself.


No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: replacing Mikunis with Amal, BSA lightning [Re: NickL] #744471
08/05/18 4:44 am
08/05/18 4:44 am
Joined: Aug 2014
Posts: 1,816
OZ
Triless Offline
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OZ
Obviously, Nick, you are talking about the twin choke automotive type delOrtos, which are a mean looking carb, like the equivalent Weber. But, in ugly, a squarebody delOrto Concentric type beats a VM Mikuni slides down !
Personally, although Amals have done alright for me over the years, I have a 32mm VM Mikuni on my single carb Triumph 750 special, and I don't think its ugly at all ! And, as some uncharitable bastard said, compared to the owner, it isn't at all !

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744474
08/05/18 5:22 am
08/05/18 5:22 am
Joined: Dec 2013
Posts: 4,571
ohio, usa
kevin roberts Offline

DOPE
kevin roberts  Offline

DOPE

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Posts: 4,571
ohio, usa
i find keihins to be the aesthetic carburetor of choice:

[Linked Image]


"Are bikes so nice as all that?" asked the mole, shyly...

"Nice? They're the only thing," said the Water Rat Solemnly, as he leaned forward on the handlebars. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about with bikes."
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744477
08/05/18 5:52 am
08/05/18 5:52 am
Joined: Aug 2001
Posts: 137
Anchorage Alaska USA
M
Mitch Offline
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Posts: 137
Anchorage Alaska USA
wow.... ish. those look terrible. please doc, put the tumors (AMAL) back in

Re: replacing Mikunis with Amal, BSA lightning [Re: Andy Higham] #744512
08/05/18 2:16 pm
08/05/18 2:16 pm
Joined: May 2004
Posts: 3,892
Sydney Australia
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BSA_WM20 Offline
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Sydney Australia
Originally Posted by Andy Higham
The Mikuni has several advantages over the AMAL, not all of these were adressed in the premier series
The AMAL is made out of poor material and wears out prematurely
The AMAL manufacturing tolerances are poor
The Mikuni pilot/idle circuit is far superior to that of the AMAL
The Mikuni has a proper cold start system
The Mikuni is spigot mounted giving good heat and vibration insulation
The Amal flange mount is poorly designed and prone to distortion


I will dispute this till the day I die.
Metallurgically the zinc alloys used to make the Concentric carb was STATE OF THE ART FOR IT'S DAY. and the EXACT SAME ALLOY is still used by almost every carb company and has been so for decades.
When used as daily transport they do not wear out prematurely.
Fuel vapour gets adsorbed into the oxide coatings of the slide & body making an exceptionally good well lubricated sliding surface.
When used ones every year, the oxide coating dries out and stiction occurs.

AMAL tollerances were absolutely fine, milions of miles of trouble free riding will attest to that.
My B40's ran the same 626's that were fitted at the factory for thousands of miles over the 12 years that they were my daily transport, weekend transport & holiday transport.
The carbs were callibrated for the DELIBERATE loose fit and work extreamely well.
In fact the big troubles came when engineers tried to resleeve them and found once they tightened up the running clearances the jetting was so far out it was not funny.
FWIW I pulled one of the 626's off the said same B40 ( waiting for a new big end ) and ran it 20,000 + miles on the WM20 with no problems after I got the jetting sorted.

The biggest problen was the ILLETERATE owners who could not or would not do as instructed and just snug them up on the O ring but decided to replace the "CHEAP" 1/2 nuts ( done to prevent overtightening ) with full size nuts done up tighter than head bolts.
After that was the "SEXY" bell mouths cause we were all GP racers so could not afford the restrictions in air flow the filters created ( a crime I must plead guilty to for a while in my youth ).
The simple fact that now , 50 year after they were introduced there are still thousands of British bikes out there still running the Concentrics they left the factory with attests to the suitability of the carb.
Now they might be running poorly, but they are still running, not what I would call a sign of a badly designed carb , made from poor materials to sloppy tolerances.
And yes there were and are better carbs out there , just the same as there were better carbs availible for just about every car even made, if the owner wanted better performance.
Enfield specified carbs without O rings , so I was told when asking about a Concentric without a groove in it amd I am jet to her an Enfield owner complain about a warped Concentric.

Last edited by BSA_WM20; 08/05/18 2:18 pm.

Bike Beesa
Trevor
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744521
08/05/18 4:02 pm
08/05/18 4:02 pm
Joined: Aug 2015
Posts: 1,301
Bolton Lancs UK
A
Andy Higham Offline
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Andy Higham  Offline
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Bolton Lancs UK
Every other carb manufacturer may have used the same material BUT made the slide of brass or hard anodised alloy.
Even after only a couple of thousand miles if you take the slide out of a Concentric you will see where it has worn against the opening in the body and your fingers will be grey from the worn away metal particles.
Pay particular attention to the nib at the top of the slide, this wears allowing the slide to twist and lock
BTW the 626 etc are far superior to the Concentric, there was one design consideration for the Concentric, to be able to supply a pair to BSA/Triumph for less than £5


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: replacing Mikunis with Amal, BSA lightning [Re: ferretjuggler] #744524
08/05/18 4:22 pm
08/05/18 4:22 pm
Joined: Aug 2005
Posts: 1,549
melbourne florida
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bodine031 Offline
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melbourne florida
So my 1964 A-65 SF/Hornet with 2 mono blocks was never made????

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744525
08/05/18 4:43 pm
08/05/18 4:43 pm
Joined: Aug 2001
Posts: 4,230
argyll. scotland, uk
gavin eisler Offline
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gavin eisler  Offline
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Posts: 4,230
argyll. scotland, uk
Misspelling illiterate, brilliant, genuinely laughed out loud, good post Trevor.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: replacing Mikunis with Amal, BSA lightning [Re: Andy Higham] #744526
08/05/18 4:52 pm
08/05/18 4:52 pm
Joined: Aug 2001
Posts: 7,668
scotland
triton thrasher Online content
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triton thrasher  Online Content
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Posts: 7,668
scotland
Originally Posted by Andy Higham
BTW the 626 etc are far superior to the concentric, there was one design consideration for the concentric, to be able to supply a pair to BSA/Triumph for less than £5


The 626 is a Concentric.


Amateur Loctite enthusiast.
Re: replacing Mikunis with Amal, BSA lightning [Re: triton thrasher] #744539
08/05/18 6:59 pm
08/05/18 6:59 pm
Joined: Aug 2015
Posts: 1,301
Bolton Lancs UK
A
Andy Higham Offline
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Andy Higham  Offline
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Joined: Aug 2015
Posts: 1,301
Bolton Lancs UK
Sorry! My bad I was thinking 276 series (pre monoblock)


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744551
08/05/18 8:24 pm
08/05/18 8:24 pm
Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Posts: 4,591
Owego, NY, USA
It looks to me that the OP was not asking for a debate on the various advantages or disadvantages of Mikunis vs. Amals. It's also not clear what sort of advice is sought. Originality? BSA used Monoblocs on Lightnings through 1967, then switched to Concentrics in '68. Reliability/ease of use? Monoblocs are good-performing carburetors, but complex compared to Concentrics - many more parts, more places to leak, etc.

Redrooster, if your objections to Mikunis are fit, appearance, and/or jetting difficulties, and you're considering any non-AMAL alternative, check out JRC carbs. There were one or two lengthy threads on these recently. JRCs are basically PWK flat-slide carbs that are modified to fit British bikes. They are about the same size as Amals, and are available in flange mount or spigot mount, and with mouths threaded to accept screw-on AMAL air cleaners, or smooth for clamp-on air cleaners, and jetting is customized to particular marques/models by JRC. I've heard now four or five "bolt on and go" success stories.



Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: Triless] #744564
08/05/18 10:18 pm
08/05/18 10:18 pm
Joined: Jan 2014
Posts: 4,163
Aus
N
NickL Offline
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NickL  Offline
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Aus
Originally Posted by Triless
Obviously, Nick, you are talking about the twin choke automotive type delOrtos, which are a mean looking carb, like the equivalent Weber. But, in ugly, a squarebody delOrto Concentric type beats a VM Mikuni slides down !
Personally, although Amals have done alright for me over the years, I have a 32mm VM Mikuni on my single carb Triumph 750 special, and I don't think its ugly at all ! And, as some uncharitable bastard said, compared to the owner, it isn't at all !


No Stephen, i was talking about the bike carbs fitted to dukes, mv's etc. Several guys i raced with used them back in the 70's. They were nicely made and looked good.
My preference for using a weber or Delorto on my racing bike is a different thing altogether, they just work brilliantly but are very bulky.

The JRC's that Mark talked about are an option i've yet to try on any bike but reports are good and the carb spec is fair.
Proper cold start, chrome slide, decent float arrangement, flat type slide etc.
When my ones are clapped out ,i think i will give them a try.

I don't think anyone is disagreeing with Trevor about the fact there are millions of happy AMAL users but, like Lucas they had
to produce stuff for next to nothing and in many cases it shows.

Last edited by NickL; 08/05/18 11:17 pm.

No-one expects the Spanish Inquisition................
Bring in the 'Comfy Chair'
Re: replacing Mikunis with Amal, BSA lightning [Re: Mark Z] #744627
08/06/18 12:40 pm
08/06/18 12:40 pm
Joined: Nov 2013
Posts: 295
Bristol England
R
redrooster Offline OP
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redrooster  Offline OP
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Bristol England
Thanks for all replies,
Ferret, yes bike was originaly A65 Star and has had lightning head (year not known) fitted. Ignition is Boyer
Too late to restore to original (spent last 5 years going in the opposite direction) and the Mikuni carbs look great on my bike.. Just having starting problems with them and running lean problems. Also the mounting rubbers keep shearing as the carbs bounce up and down because they are not fixed at the inlet end.

I am looking at the AMAL Concentric premiers because I fitted them to my 1970 T120 which I had carb problems with and it ran perfect on these straight out of the box.


Just need advice from anyone with experience of either carb on there lightning.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744644
08/06/18 3:22 pm
08/06/18 3:22 pm
Joined: May 2004
Posts: 3,892
Sydney Australia
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BSA_WM20 Offline
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Sydney Australia
The lightning ran concentrics ( for the few years it ran ) without any problems.
But then they were always run with the filters on .
Without filters a dust gets sucked into the primary air inlet and blocks up the primary fuel circuit.
Like all carbs, leaving them sitting for 3 months full of fuel will result deposits in all the passage ways that is really difficult to remove.
When used daly I never had any problems witht them.
Like a lot of things in the day they required servicing , along with points that got adjusted every months & tappets .
So an annual needle & needle jet plus a new slide every couple of years was about it for parts and a sync every 6 months or so to compensate for cable stretch .

OTOH when I was in town & club members would come by it was not rare to see needle jets flogged out 3 times longer than wide, ridges worn in the slides and the bike running on only one carb at idle.
But even with that sort of abuse, the bike ran. Neglect any other carb like that and you will be doing a lot of pushing.
The Mikuni is a better carb, no arguement about it, however it is no where near as tolerant as the concentrics are and you will need to tune them properly or they just won't work.
Leave them sitting over winter full of fuel and there is a better than average chance you will not be able to resurect next year.
One of the problems with dissimilar metals is galvanic corrosion, particularly if they are subject to dew condensation over winter.

The biggest problem is we look at them through modern eyes and compare them to modern carbs so naturally they fall short
Now if you want a painful job try matching a set of 4 CV carbs and keep them in sync over the entire rev range.

I have just bought a box full of new premier concentrics for the bikes I will be riding till I fall off my perch.
The M20 just got its new 626 & there is another for the B40 the B44 & B50 plus a pair for the A65L & T which most likely will never get finished.

Last edited by BSA_WM20; 08/06/18 3:25 pm.

Bike Beesa
Trevor
Re: replacing Mikunis with Amal, BSA lightning [Re: BSA_WM20] #744657
08/06/18 4:57 pm
08/06/18 4:57 pm
Joined: Nov 2013
Posts: 295
Bristol England
R
redrooster Offline OP
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redrooster  Offline OP
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Bristol England
Hi WM20,
Thank you for your reply.
So your on the AMAL side of the fence.
My carbs are spotless inside and out so those issues can be ruled out.


Me, still thinking like a tortoise and changing mind constantly. Changed the pilot jet on the mikuni yesterday from 25 to 30 and it did seem to improve starting and plug colour but maybe flukey, will see.
I spoke to the suppliers of Mikuni carbs in England today regarding the shearing/splitting of the rubber mounting to the head and was advised to support the rubber carb mounting by some other means. Suggestions I thought strange, home made brackets, support wires etc,blah. Am I missing something and being plank thick here ?


Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744658
08/06/18 5:03 pm
08/06/18 5:03 pm
Joined: Nov 2013
Posts: 295
Bristol England
R
redrooster Offline OP
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Bristol England
Can anyone post a picture of how they have mounted there Mik's on a brit bike twin ?

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744661
08/06/18 5:20 pm
08/06/18 5:20 pm
Joined: Aug 2005
Posts: 1,549
melbourne florida
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bodine031 Offline
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melbourne florida
Mite try 3/4 to 1 turn out on the A/M screw. I use Gates brand green stripe hose holds up my round slides just fine with pod A/Filters

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744715
08/07/18 1:36 am
08/07/18 1:36 am
Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Owego, NY, USA
Originally Posted by redrooster
Can anyone post a picture of how they have mounted there Mik's on a brit bike twin ?


This help?

[Linked Image]

One thing I can tell you, the rubber couplers they supply with Miks are crap. I use automotive fuel filler hose, you know, the hose that goes from your filler cap to the fuel tank.

Are your Miks 30 or 32mm? Mine are 32s, which, being oversized (stock Amals are 30mm), presents a jetting problem in itself. If yours are 32mm, I may be able to help with jetting info.




Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744740
08/07/18 8:13 am
08/07/18 8:13 am
Joined: May 2004
Posts: 3,892
Sydney Australia
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BSA_WM20 Offline
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Sydney Australia
Originally Posted by redrooster
Hi WM20,
Thank you for your reply.
So your on the AMAL side of the fence.
My carbs are spotless inside and out so those issues can be ruled out.


Me, still thinking like a tortoise and changing mind constantly. Changed the pilot jet on the mikuni yesterday from 25 to 30 and it did seem to improve starting and plug colour but maybe flukey, will see.
I spoke to the suppliers of Mikuni carbs in England today regarding the shearing/splitting of the rubber mounting to the head and was advised to support the rubber carb mounting by some other means. Suggestions I thought strange, home made brackets, support wires etc,blah. Am I missing something and being plank thick here ?



There is nothing wrong with Mikunis and when set up properly they will work better than a Concentric, which is no surprise as they are a latter developement of the Concentric so they should.
IMHO fitting them is a "lipstick on a pig modification". Lots of hassels for little gain.
OTOH if you are a have to tinker type go ahead.
If you are lucky you might get a small increase in the fuel economy and they will accelerate better so if standing 1/4 miles are your bag then go ahead.
However bikes of our era won many many many races fitted with the humble Concentric and there is no need to replace them now days .
If you want to toss monos and beat everything off at the lights, buy a modern 250 super sports bike.


Bike Beesa
Trevor
Re: replacing Mikunis with Amal, BSA lightning [Re: Mark Z] #744741
08/07/18 8:22 am
08/07/18 8:22 am
Joined: Nov 2013
Posts: 295
Bristol England
R
redrooster Offline OP
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Bristol England
Hi Mark,
Judging by your photo I am being plank thick and will be looking at doing this set up.
Mik's are 30mm.
Bodine, idles highest at 2 turns out so have set a/m to 11/2. Everything I have read says no less than 11/2 so have been reluctant to go to 1. So I changed pilot jet from 25 to 30. This did not seem to change idle so left it at 1 1/2 out Is this the wrong approach ?

Re: replacing Mikunis with Amal, BSA lightning [Re: kevin roberts] #744744
08/07/18 9:45 am
08/07/18 9:45 am
Joined: Dec 2017
Posts: 31
Athens Greece
Konstantinos Offline
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Athens Greece
I wanted to have a pair of keihins on my T140 eight valve to see how it runs on the road.
I am very sure that works great.
And I am sure that your bike is flying with them but they are not looking good on classic Brit bike like the box section swingarm on my featherbed trident works great but not looking good to be honest
I think the reason is what you want from your bike.
If you want performance you need modern goodies.
If you want classic look have to stuck with stock parts.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744757
08/07/18 1:48 pm
08/07/18 1:48 pm
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Posts: 1,549
melbourne florida
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bodine031 Offline
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melbourne florida
I have a single 30mm Kuni on my 64 Hornet. clip in the middle, low jet around where you are, 1 turn out on the A/F screw and it starts and idles hot ,warm, cold just fine. pulls off idle fine
B-B ign. with (1) 3 ohm dual tower 12v factory HD take of coil. That's my set up that works for me that bike. I ride it everyday using reg/unleaded go juice with no additives

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744781
08/07/18 6:28 pm
08/07/18 6:28 pm
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Posts: 295
Bristol England
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redrooster Offline OP
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Bristol England
Hi all, the mik's came in a box with the bike when I got it so I have been riding with them for a while, judging by all replies I think I will persevere and get them right, sort out the mounting and all should be good. Been persuaded off of the Amals.

Konstantinos, my bike is not classic look or build Brief description is 64 star,69 or 70 or 71 later lightning head ? ,mikuni carbs, old Boyer ignition (micro power with micro power ignition coil). External oil filter fitted with later splitter/top end feed (69 I think) fitted before filter and outside of tank, Gold star front end with Eddie Dow TLS brakes, strange bars but comfortable (found in parts pile) that no bar end mount mirrors fit in to ?, Front light of unknown origin, Smiths clock on custom mount. Rear frame chopped and rigid, custom built seat (one rider only), back rest, oil tank, chain guard , rear fender. rear light mount, oil filter mount. Think I might be getting carried away here but.

You either love it or hate it, to me it is a work of genius.

Re: replacing Mikunis with Amal, BSA lightning [Re: bodine031] #744783
08/07/18 6:48 pm
08/07/18 6:48 pm
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Bristol England
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redrooster Offline OP
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Hi Bodine,

So your clip is on 3, but your bike is way different.
Clip is on 4, cutaway 2 1/2, pilot jet 30 screw 1 1/2 out and still looking lean.

I have decided to look at this in another way, I will keep the Mik's , mount them properly as the advise I have had.
Then start on the jetting

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744799
08/07/18 8:19 pm
08/07/18 8:19 pm
Joined: Sep 2004
Posts: 899
Farnham, Surrey, UK
gunner Offline
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Farnham, Surrey, UK
Hi Redrooster,

I have a 68 A65 Firebird fitted with AMAL 930 carbs (not the Premier version). I purchased these carbs from Burlen about 6 years ago when I was completing the rebuild of my bike. So far these carbs have performed well although my annual mileage is limited due to parenting commitments. I deliberately omitted the choke slides from both carbs as I felt this was a useless design and I can easily start the bike just using the ticklers, even in the UK winter. My feeling is that the standard AMAL Concentric is a good carb when new but it does have some drawbacks as already noted. Part of the problem is that it was not a high quality design when new and when combined with poor maintenance over several decades a bad reputation arises. I have no doubt the new Premier carb is better and more durable than the original AMAL Concentric, however I think we should show some respect (as Trevor suggests) to all the millions of concentrics which have kept BSA's, Nortons, Triumphs etc. running for all these years.

For what its worth, I'm running a single Mikuni 34 on my 750 Norton. It runs great and starts virtually first kick helped by the choke lever/enrichment circuit. I'm also using a JRC carb on my B44 also with a choke lever/enrichment circuit. Agreed that these carbs may look slightly odd on a British bike, but they do have a plus side.

I would keep the Mikuni;s and just get them jetted right. Maybe you can find a rolling road nearby and get them dialled in spot on.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744807
08/07/18 8:49 pm
08/07/18 8:49 pm
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ohio, usa
kevin roberts Offline

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ohio, usa
Originally Posted by redrooster
Can anyone post a picture of how they have mounted there Mik's on a brit bike twin ?


[Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image]

maybe there's something useful here? i've run 32mm and now 34mm mikunis on my morgo commuter for almost 40 years, and also use the same mounts for the keihin FCRs inb my LSR machine.

spigots are available for bothe the screw-in and bolt-on carburetor manifolds.

side covers on an OIF are always an issue. i used to use 1976 honda CB360 covers, which are a perfect fit. now i just don't run any. on a dry frame, carb extensions bump into the oil tank, but short mikunis shouldn't be a problem.


"Are bikes so nice as all that?" asked the mole, shyly...

"Nice? They're the only thing," said the Water Rat Solemnly, as he leaned forward on the handlebars. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about with bikes."
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744809
08/07/18 9:01 pm
08/07/18 9:01 pm
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Posts: 31
Athens Greece
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Athens Greece
Hi Redrooster,
I thought that you have a stock bike with modified engine but it' s modified at all
So no problem to keep VM because unfortunately they are much reliable than Amals
Just be sure to have right jets and good quality rubber manifolds
VM have old classic look.
My first reply was for Kevin with keihins.
Here in my country most of my friends have on their british bikes single VM because it' s more easy to fix it
But friends with old dual concentrics are faster so if you have dual VM are better at all.
I hear that old concentrics are much better than new and I have experience with my T140 when It was with stock head
And AMAL MKII 30mm with made in England bodies never had problems for many miles but when I modified to eight
valve and fitted New 36 mm AMAL MKII made in Spain after of 15.000 km the slides were bordeline.
So keep Mikunis I have the same opinion with gunner.


Re: replacing Mikunis with Amal, BSA lightning [Re: kevin roberts] #744816
08/07/18 9:42 pm
08/07/18 9:42 pm
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England
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ferretjuggler Offline
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England
Originally Posted by kevin roberts
Originally Posted by redrooster
Can anyone post a picture of how they have mounted there Mik's on a brit bike twin ?


[Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image][Linked Image]

maybe there's something useful here? i've run 32mm and now 34mm mikunis on my morgo commuter for almost 40 years, and also use the same mounts for the keihin FCRs inb my LSR machine.

spigots are available for bothe the screw-in and bolt-on carburetor manifolds.

side covers on an OIF are always an issue. i used to use 1976 honda CB360 covers, which are a perfect fit. now i just don't run any. on a dry frame, carb extensions bump into the oil tank, but short mikunis shouldn't be a problem.

Just out of interest what sort of gas milage are you getting with twin 34mm Mikuni VMs ?
I've got no experience of them on a Triumph, but I swapped the 34mm Mikuni CV carbs on my XS650 for a pair of 34mm Mikuni VM slide type.
Turned it from a tame little kitten into a ferocious snarling beast - with no other mods.
But fuel economy went from 50+ mpg (imperial gallons) to the low 30s

Re: replacing Mikunis with Amal, BSA lightning [Re: Konstantinos] #744817
08/07/18 10:10 pm
08/07/18 10:10 pm
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ohio, usa
kevin roberts Offline

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ohio, usa
Originally Posted by Konstantinos
I wanted to have a pair of keihins on my T140 eight valve to see how it runs on the road.
I am very sure that works great.
And I am sure that your bike is flying with them but they are not looking good on classic Brit bike like the box section swingarm on my featherbed trident works great but not looking good to be honest
I think the reason is what you want from your bike.
If you want performance you need modern goodies.
If you want classic look have to stuck with stock parts.


i'm sorry, konstantinos, i missed this post of yours.

yes, what you change on the machine you ride is completely a function of what you want from it. if complete originality is the most important thing, then you must use original-style carbs. but you must also do without electronic ignition, modern tires, brighter lights, updated charging systems, and so on. most people compromise somewhere in the middle.

i use the keihins for a race machine. they would work very well on a street bike with a fabricated airbox, but i have used mikunis on the street for decades and they work well for me. i also have some concentrics, and they work too, but when they wear out i usually replace them with mikunis.


"Are bikes so nice as all that?" asked the mole, shyly...

"Nice? They're the only thing," said the Water Rat Solemnly, as he leaned forward on the handlebars. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about with bikes."
Re: replacing Mikunis with Amal, BSA lightning [Re: ferretjuggler] #744820
08/07/18 10:17 pm
08/07/18 10:17 pm
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Posts: 4,571
ohio, usa
kevin roberts Offline

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ohio, usa
Originally Posted by ferretjuggler

Just out of interest what sort of gas milage are you getting with twin 34mm Mikuni VMs ?
I've got no experience of them on a Triumph, but I swapped the 34mm Mikuni CV carbs on my XS650 for a pair of 34mm Mikuni VM slide type.
Turned it from a tame little kitten into a ferocious snarling beast - with no other mods.
But fuel economy went from 50+ mpg (imperial gallons) to the low 30s



boy, i don't know. i never measure it. 35 years ago my machine was an unmodified 650 with concentrics, and got 43 mpg, US gallons. then i installed 32mm VM mikunis with no changes and highway mileage went to 55 mpg. then i had the head worked on and installed a 750 kit and the mileage went down to 42 again.

i broke one one of the 32s trying to get a float needle out and replaced them with VM34s. the 34s are more compatible with the original headwork and the bike is quite comfortable on the street. i've never measured the fuel mileage, but i'm running 21/47 gearing on it too, so that would have an effect. i tend to keep the rpms higher than i did with 19/47, so i probably get poorer fuel economy.

the 35mm keihin FCRs get about 7.2 mpg on my race 650, but that's not really comparable.


"Are bikes so nice as all that?" asked the mole, shyly...

"Nice? They're the only thing," said the Water Rat Solemnly, as he leaned forward on the handlebars. "Believe me, my young friend, there is nothing -- absolutely nothing -- half so much worth doing as simply messing about with bikes."
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744853
08/08/18 3:31 am
08/08/18 3:31 am
Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Owego, NY, USA
Originally Posted by redrooster
Hi Mark,
Judging by your photo I am being plank thick and will be looking at doing this set up.
Mik's are 30mm.
Bodine, idles highest at 2 turns out so have set a/m to 11/2. Everything I have read says no less than 11/2 so have been reluctant to go to 1. So I changed pilot jet from 25 to 30. This did not seem to change idle so left it at 1 1/2 out Is this the wrong approach ?


Ok. FWIW, my filters are Uni foam (sold in a sheet), soaked with Uni filter oil, over 3/16" wire mesh, all held on with hose clamps. Because of the small surface area, the foam needs to be cleaned (with gasoline) and re-oiled regularly. Triumphs and OIF BSAs offer more options for air cleaners, as shown in Kevin's photos, but on a dry frame BSA, there is only about 1/2" clearance between the carb mouths and the frame.

If it idles highest at 2 turns out, then that would seem to be the correct setting, no? Out = leaner, In = richer, so if you really want it at 1 1/2, I think you're going the wrong way with the pilot jet. (They do make a 22.5 pilot jet.)

When you get it where you think you want it, a good test of the idle mixture is this: Start and warm up the engine so it can be re-started without enrichening. Put in new plugs and re-start the engine. Let it idle for a few minutes without touching the throttle. Shut it down and look at the plugs.

Always let the head cool for about 10 minutes before removing the plugs, and always use the anti-seize lubricant that's made for spark plugs on the threads.




Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: Mark Z] #744876
08/08/18 9:19 am
08/08/18 9:19 am
Joined: Nov 2013
Posts: 295
Bristol England
R
redrooster Offline OP
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Bristol England
Hi Mark,
Ok, I changed the 25 for a 30 to make it richer and have made it leaner ?, I have 20 it my box I should try this.

Hi Ferret,

I see the aluminium adaptors on your photos that bolt straight on to the head, this is what I think I need but can,t seem to find them supplied by anyone here.will look harder.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744877
08/08/18 9:47 am
08/08/18 9:47 am
Joined: Aug 2001
Posts: 4,230
argyll. scotland, uk
gavin eisler Offline
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argyll. scotland, uk
"Ok, I changed the 25 for a 30 to make it richer and have made it leaner ?, I have 20 it my box I should try this."

No .

When you put in the 30 the jet passes more fuel so the screw ends up at 2 turns for the correct balance, more fuel needs more air, the screw controls the air flow. try the 22.5 if you must have correct balance at 1.5 turns out.


Last edited by gavin eisler; 08/08/18 9:48 am.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: replacing Mikunis with Amal, BSA lightning [Re: gavin eisler] #744882
08/08/18 11:35 am
08/08/18 11:35 am
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Bristol England
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redrooster Offline OP
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Ok got it, happy where I am now with the 30

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744918
08/08/18 7:11 pm
08/08/18 7:11 pm
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Bristol England
R
redrooster Offline OP
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Bristol England
Hi all,
Your photos and advice is really appreciated, I am going to put this into practice and will let you know how it turns out.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744928
08/08/18 9:03 pm
08/08/18 9:03 pm
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Bolton Lancs UK
A
Andy Higham Offline
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Bolton Lancs UK
Look at plate manifolds in the lower half of This page, they take up less space than the adaptor/rubber sleeve arrangement


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744930
08/08/18 9:08 pm
08/08/18 9:08 pm
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Posts: 1,301
Bolton Lancs UK
A
Andy Higham Offline
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Bolton Lancs UK
On a B31 engine
[Linked Image]20170125_170939 by Sigma Projects, on Flickr
On a DBD type engine
[Linked Image]20180609_152238 by Sigma Projects, on Flickr


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #744945
08/09/18 1:24 am
08/09/18 1:24 am
Joined: Aug 2001
Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Owego, NY, USA
Originally Posted by redrooster
Hi Mark,
Ok, I changed the 25 for a 30 to make it richer and have made it leaner ?, I have 20 it my box I should try this.


What Gavin said. I didn't explain it very well. Right, if you're happy with two turns out on the air screw, then leave in the 25 jet. If you want the air screw in farther (richer), then you want a smaller pilot jet to compensate.

Originally Posted by redrooster
Hi Ferret,I see the aluminium adaptors on your photos that bolt straight on to the head, this is what I think I need but can,t seem to find them supplied by anyone here.will look harder.


This may not help you over there, but I got my Mikuni kit from M.A.P. Cycle in Florida, which kit included the manifold adapters.



Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: Mark Z] #749968
09/21/18 10:25 am
09/21/18 10:25 am
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Bristol England
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redrooster Offline OP
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[Linked Image]


Hi all,
Thanks for help this is what I ended up with

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #750141
09/23/18 12:58 am
09/23/18 12:58 am
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Owego, NY, USA
Mark Z Offline
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RR, I don't know how well it will show up in this picture, but if you want to get some rudimentary filtering, you may want to try something like this:

[Linked Image]

"Filters" are 3/16" square galvanized wire mesh covered with oil-soaked Uni foam, all held on with hose clamps. Because of the small surface area, they need to be periodically cleaned (with gasoline) and re-oiled, but it's better than nothing.

Also, I have only about 1/8" between the two spigot mount clamps, and it looks like you have about 1/4". You may be able to gain a bit of clearance by cutting the coupler and/or the manifold adapter a bit shorter.



Last edited by Mark Z; 09/23/18 1:05 am. Reason: screwed up the picture the first time

Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #750299
09/24/18 2:55 pm
09/24/18 2:55 pm
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Bristol England
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redrooster Offline OP
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Hi Mark
Thanks, yes will do something like this.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #753138
10/17/18 4:46 pm
10/17/18 4:46 pm
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Bristol England
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redrooster Offline OP
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[Linked Image]

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #753139
10/17/18 4:52 pm
10/17/18 4:52 pm
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Bristol England
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redrooster Offline OP
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Hi Mark and everyone,
Advice is really appreciated, Bike is running beautiful

and it goes on and on and on

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #753322
10/19/18 3:04 am
10/19/18 3:04 am
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Owego, NY, USA
Mark Z Offline
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RR, I like your air filters better than mine! What are they? Did you make them, or are they "store-bought"? Held on with set screws?



Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #756510
11/18/18 9:08 pm
11/18/18 9:08 pm
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Bristol England
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redrooster Offline OP
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Hi Mark, been away for a bit, Air filters are velocity stacks bought from a US website, they came with wire mesh gauze filter but have fitted the foam over. they are secured with 3 grub screws, Will try to find where I got them from.

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #757548
11/29/18 9:03 pm
11/29/18 9:03 pm
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Bristol England
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redrooster Offline OP
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Hi Mark,
Just remembered, they are from Dime City Cycles 'polished aluminium shorty velocity stacks'

Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #757574
11/30/18 1:22 am
11/30/18 1:22 am
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Posts: 4,591
Owego, NY, USA
Mark Z Offline
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Mark Z  Offline
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Owego, NY, USA
Red, got your PM, thanks! I'll check out Dime City!

Ok, got 'em bookmarked. One more question, if you don't mind: How do you keep the foam in place?





Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: replacing Mikunis with Amal, BSA lightning [Re: Mark Z] #758007
12/03/18 9:17 pm
12/03/18 9:17 pm
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Bristol England
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redrooster Offline OP
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Hi Mark,
Just cut the foam slightly larger than the metal gauze supplied and fit in front of the gauze,when the stack is pushed onto the carb it is held in position along with the gauze.,
Bit fiddly but probably 1/2 hour job. Cut well oversize first then trim.

Last edited by redrooster; 12/06/18 7:47 pm.
Re: replacing Mikunis with Amal, BSA lightning [Re: redrooster] #758765
Yesterday at 07:11 AM
Yesterday at 07:11 AM
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Gnashville
DavidP Offline

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Originally Posted by redrooster
Hi all, the mik's came in a box with the bike when I got it so I have been riding with them for a while, judging by all replies I think I will persevere and get them right, sort out the mounting and all should be good. Been persuaded off of the Amals.

Your choice. I put Miks on my 71 A65. I really wanted Mk2 Amals, but the Miks were cheap so I went with that. Many jets changes later they work well. However, I only get 35mpg, where I used to get 40-45 with the Amals.
They can look very "trick," if that's what you're after, but they are relatively huge, space is limited, as are options for mounting.
FWIW: I'm going back to Amals on this bike. They might be junk-metal crap, but they fit the bike. Might not be as fast as the Miks, but if I wanted to go fast I would not be riding 45 year-old bikes.
Good luck with getting the jetting correct. laughing


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
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