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Jetting Keihin CRs #707731
09/08/17 5:25 pm
09/08/17 5:25 pm
Joined: Sep 2017
Posts: 11
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Matchless Offline OP
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Hello to everyone. This is my first post on BBF.
Some time ago now I built an O.I.F T160. The engine is 930cc with all the usual goodies including Megacycle 51B cams, 9.5:1 omegas, Carillo rods etc. At first I had a 3 into 2 exhaust system made by NRP & fitted a set of Mikuni BST carbs from a Hinckley Trident. After three dyno sessions I gave up trying to get the thing running properly & fitted a set of 31mm Keihin CRs. With these fitted it still would not run properly.
The next step was to take it to P&M who checked everything & concluded that the exhaust must be the problem. They built a 3 into one & set the carbs as best they could, but it still does not run well enough. It seems lean on up to quarter throttle then too rich above this. So far I have tried YY6, YY7, & YY8 needles in various positions. The mains are 125, pilots 78, main air jet (in venturi) 230, & throttle slides are 3.0.
Does anyone out there have any ideas or know of a dyno operator in the UK who knows these carbs well?

Thanks in advance, Martyn.

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Re: Jetting Keihin CRs [Re: Matchless] #707740
09/08/17 6:37 pm
09/08/17 6:37 pm
Joined: Jun 2002
Posts: 10,234
Scotland
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Stuart Offline
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Scotland
Hi Martyn,

Firstly, welcome to the Forum.

One thing you haven't posted is the diameter of the carbs. you're using. Reason I can look like a clever-clogs wink is I just checked the Triples On Line forum and different posts mention different diameters. Depending how much good info. you get here, try the TOL Advanced Search and follow the returned links?

Hth.

Regards,

Re: Jetting Keihin CRs [Re: Stuart] #707802
09/09/17 9:11 am
09/09/17 9:11 am
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Posts: 11
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Matchless Offline OP
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Hi Stuart,

I did state the size as 31mm.

Re: Jetting Keihin CRs [Re: Matchless] #707805
09/09/17 10:32 am
09/09/17 10:32 am
Joined: Jun 2002
Posts: 10,234
Scotland
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Stuart Offline
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Stuart  Offline
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Scotland
Oooops ...

Re: Jetting Keihin CRs [Re: Matchless] #707807
09/09/17 10:44 am
09/09/17 10:44 am
Joined: Oct 2012
Posts: 3,999
Running from demons in WNY
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Running from demons in WNY
My Triumph race bike has spent a bit of time on a chassis dyno...It my opinion that a chassis dyno serves best for full throttle main jet sizing.....Part throttle works out best real live road testing...With a modified engine and custom exhaust part throttle jetting can be difficult ,usually due to reversion... What exactly do you mean by the the " engine won't run properly? And you're sure the cam timing is where it belongs?


I ride dinosaurs that eat money
Re: Jetting Keihin CRs [Re: Hillbilly bike] #707815
09/09/17 12:19 pm
09/09/17 12:19 pm
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Matchless Offline OP
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The cam timing as set by me is spot on & was checked & confirmed by P&M when they had the bike. The bike flies once over half throttle but bogs down at lower openings. It seems to be rich so I changed the yy7 needles for yy8. This improved the lower part of the throttle but made it much worse above i.e too rich. This does not make any sense to me, as the yy range of needles are all the same in the taper region. The only difference is the top parallel section which differs by approx .002" for each number.
What I was hoping for was someone with a similar set up to my bike who could give me some carb settings.

Re: Jetting Keihin CRs [Re: Matchless] #707816
09/09/17 12:30 pm
09/09/17 12:30 pm
Joined: Oct 2012
Posts: 3,999
Running from demons in WNY
Hillbilly bike Online content
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Joined: Oct 2012
Posts: 3,999
Running from demons in WNY
Sounds like reversion....I had a Triple years ago and installed a three into one exhaust...Top end improved but low end suffered from reversion due to the exhaust tuning.The solution was a one inch balance pipe between the pipes about 12 inches from the head....My race bikes also have reversion so I'm familiar with it...you mentioned P&M also suspected the exhaust so you got a different exhaust....Still having a problem so perhaps it's still the exhaust? What does the exhaust system on the bike now look like? Long or short primary tubes? Obviously, there can be other factors...Keihin CRs are popular on older Ducati's and usually easy to tune...But that's a 90 degree twin.....


I ride dinosaurs that eat money
Re: Jetting Keihin CRs [Re: Matchless] #707825
09/09/17 2:37 pm
09/09/17 2:37 pm
Joined: Sep 2017
Posts: 11
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Matchless Offline OP
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The P&M exhaust system is a 3 into 1 with long headers, a triangular collector, & a long tapered silencer with a straight thru perforated baffle. It looks like the type of system used on any Rob North racer.

Re: Jetting Keihin CRs [Re: Matchless] #707826
09/09/17 2:59 pm
09/09/17 2:59 pm
Joined: Aug 2005
Posts: 1,499
melbourne florida
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bodine031 Offline
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melbourne florida
Martyn ck here with Dynoman www.dynoman.net

Re: Jetting Keihin CRs [Re: Matchless] #707861
09/09/17 9:07 pm
09/09/17 9:07 pm
Joined: Oct 2012
Posts: 3,999
Running from demons in WNY
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Running from demons in WNY
Originally Posted by Matchless
The P&M exhaust system is a 3 into 1 with long headers, a triangular collector, & a long tapered silencer with a straight thru perforated baffle. It looks like the type of system used on any Rob North racer.

I assume it's a street bike? If so, what is great on a race bike might not be so great on a street bike...If the long tapered silencer is removable ,try it without...Away from your neighbors of course... grin


I ride dinosaurs that eat money
Re: Jetting Keihin CRs [Re: Matchless] #707866
09/09/17 10:31 pm
09/09/17 10:31 pm
Joined: Feb 2012
Posts: 295
Southampton UK
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Peter Gascoigne Offline
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Southampton UK
I thought P&M were supposed to be experts on Keihin CR carbs? When I asked if they could dyno my BSA A65 with PWKs fitted they said they wouldn't, but said they would if I bought a pair of CRs as that's what they knew best. I'd like to know which UK dyno firm knows Mikunis?


1971 BSA A65 Lightning "Bitsa"
1966 BSA A65 "Beezuki" with GT550 two-stroke engine
1974 Triumph T150 830cc
1975 Suzuki GT550
1975 Laverda 1000 3C
1986 Yamaha SRX 600
Re: Jetting Keihin CRs [Re: Matchless] #708065
09/11/17 6:33 pm
09/11/17 6:33 pm
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Matchless Offline OP
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Yes it is a street bike. Before I built the O.I.F T160 ALL of these engine parts were in my 1969 T150. The only differences were 27mm Concentrics & a T150 ex.manifold with Slippery Sam pipes & rayguns. The bike ran well & was fast. Unfortunately I do not have, or for that matter want to use Amals & the previous exhaust system.
As for P&M, the only conclusion they could come to, was the cams were causing the problem. This I do not believe as it ran well in it's previous incarnation.

Re: Jetting Keihin CRs [Re: Matchless] #708093
09/11/17 9:24 pm
09/11/17 9:24 pm
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Posts: 295
Southampton UK
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Peter Gascoigne Offline
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Matchless,

Did P&M give you a dyno sheet? If so it should have an air/fuel ratio line which tells you where the engine is rich/lean/just right.


1971 BSA A65 Lightning "Bitsa"
1966 BSA A65 "Beezuki" with GT550 two-stroke engine
1974 Triumph T150 830cc
1975 Suzuki GT550
1975 Laverda 1000 3C
1986 Yamaha SRX 600
Re: Jetting Keihin CRs [Re: Matchless] #708191
09/12/17 6:45 pm
09/12/17 6:45 pm
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Posts: 11
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Matchless Offline OP
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Whilst they were working on the bike their dyno broke down. If I could find a dyno operator in Britain who was really good with carbs I would travel 200 miles or more. All the ads for dynos seem to be obsessed with remapping modern biles.

Re: Jetting Keihin CRs [Re: Matchless] #708293
09/13/17 7:55 pm
09/13/17 7:55 pm
Joined: Feb 2012
Posts: 295
Southampton UK
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Peter Gascoigne Offline
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Southampton UK
The problem you have is that you need a dyno that has all the jets/needles/floats/slides for Keihin CR carbs. Stocking all the parts needed ties up a load of money, which is why dynos tend to specialise in one make, so you will probably have to go back to P&M. The reason most dynos do re-mapping is that you just need a few comms leads and you can do most things. Not to mention that there is a lot more modern bikes out there than our arcaic heaps, generally piloted erratically by eccentric luddites.

Last edited by Peter Gascoigne; 09/13/17 7:55 pm.

1971 BSA A65 Lightning "Bitsa"
1966 BSA A65 "Beezuki" with GT550 two-stroke engine
1974 Triumph T150 830cc
1975 Suzuki GT550
1975 Laverda 1000 3C
1986 Yamaha SRX 600
Re: Jetting Keihin CRs [Re: Matchless] #708304
09/13/17 9:13 pm
09/13/17 9:13 pm
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Matchless Offline OP
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After chatting with another triples fanatic today, I think my next step will be to try a larger throttle slide cut away. As he rightly pointed out, a lot of triples do seem to run better with number 4 slides in Amals. Keihins might need the same. Thanks to all for help so far. I will keep you posted.

Re: Jetting Keihin CRs [Re: Matchless] #712692
10/25/17 6:31 pm
10/25/17 6:31 pm
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Matchless Offline OP
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Just a brief update on the jetting situation. I fitted a set of 35 slides in place of 30 slides & it made a real improvement. Next up was a change to 80 pilots from 78s which improved the idle & also the low speed pickup.The YY7 needles are now on the centre clip & the bike is getting much nicer to ride. I will drop the needle one groove next, as I think it might be a tad rich when winding the throttle on. Hopefully I'm on the home stretch now.

Martyn.

Re: Jetting Keihin CRs [Re: Matchless] #713450
11/01/17 7:12 am
11/01/17 7:12 am
Joined: Feb 2015
Posts: 299
Melbourne Oz
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Steven A Offline
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Good to here. Hope you get it perfect.

where did you get your Keihins?

Re: Jetting Keihin CRs [Re: Matchless] #713456
11/01/17 10:26 am
11/01/17 10:26 am
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Matchless Offline OP
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Thanks for that. I will post as soon as it is perfect.
The Keihins came from Neil Beadling at Nova Classics. Neil is a really nice bloke to deal with, but hard to get hold of. Both P&M & Allens Performance also stock the CRs.



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