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Twin Miks on 838 #737514
06/03/18 9:56 am
06/03/18 9:56 am
Joined: Jun 2002
Posts: 204
Ipswich England
wbabojo Offline OP
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wbabojo  Offline OP
BritBike Forum member
Joined: Jun 2002
Posts: 204
Ipswich England
I am riding around on my 90 Deg engined A65 Special at the mo, and it snarls like a good'un on the overrun. It is however, a pig to start, especially when hot. Any suggestions as to how to get there with my twin Miks please? Its an SRM kit, 30mm, originally bought for a standard 650 BSA setup. I changed the mains from 190's to 230's!
Bore and Stroke is 77x90, which I think is Norton Commando-ish size, so a standard jetting for them? However, looking at Norton forums, it seems they have trouble with twin carb Mik setups, and go for the single carb kits instead. Being a 90 deg. motor, I dont have that option, so any Mik gurus here?

Custom ignition curve..
https://ewsg3g.dm.files.1drv.com/y4...th=1018&height=601&cropmode=none

Last edited by wbabojo; 06/03/18 12:33 pm. Reason: I thought of more stuff..

Gavin
You can't make a silk purse from a sow's ear.
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Re: Twin Miks on 838 [Re: wbabojo] #737582
06/03/18 9:22 pm
06/03/18 9:22 pm
Joined: Oct 2001
Posts: 247
Monclova
S
sloppyoil Offline
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sloppyoil  Offline
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S
Joined: Oct 2001
Posts: 247
Monclova
I like mikunis too. Mikunis work great but are seldom out of the box ready. Well sort of. If you have only changed the mains that's not really going to do anything for you except on the hi end. I know they give you some pilot jets I would check those first. Have you had them apart to see what size they are? Also the slide opening, what size is it? Then comes the needle jets, what size are they? Most often they come with P0's but that's not a definite. How many turns out are the pilot jets to get a decent idle? If your turning them out more than 2 you will need to change them, if you bought a kit from map you should have a few they sent with the kit. First youll need to see whats in the carbs. hard starting when hot sometimes depicts pilots and or slide opening. Always be sure the thing is timed correct before you start purchasing jets. In addition, is it easy to start when cold? do you have both enricheners on? If its really fat with the enricheners on you can change those too, but youll need to see what size they are. I just tuned my BSA today with Miks. Its just a 650 but I balanced it and run large diameter straight pipes. 190 main, 25 pilots, p0's, and 21/2 slides. But they are 30's and a smaller motor. I had a set up like this before so I just mirrored it prior to install and I got the same results. There used to be a patron here called PANIC who sold books on how to tune them in called victory library, tuning mikunis on English bikes. A very good book, I picked one up I mean years ago and it is a thorough book that can help you get them spot on. I run miks on all my bikes except the originals, they work great when they are dialed in. Good luck, and try to find a copy of that manual.

Re: Twin Miks on 838 [Re: wbabojo] #737661
06/04/18 5:42 pm
06/04/18 5:42 pm
Joined: Jun 2002
Posts: 204
Ipswich England
wbabojo Offline OP
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wbabojo  Offline OP
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Joined: Jun 2002
Posts: 204
Ipswich England
Thankyou very much for the links Sluggo650PNW. 95 octane unleaded pump fuel. I bought a hard copy from Victory Libraries Mikuni manual years ago, when I originally bought the carbs new from SRM. Can I find it? Can I f**k! I am off work on Thursday so I've pencilled in a workshop session. I'll go over the tappet clearance (rotating), and sycnc the throttle slides, on drillbits before checking enrichners, thanks.
Just for reference, I have twelve volts when starting, and a good charging circuit, as observed on AO Services Battery status monitor.
Sloppyoil I have the carbs complete as supplied to fit a unit twin BSA. I have since bought pairs of jets in increments to avoid catastrophic engine damage haha.


Gavin
You can't make a silk purse from a sow's ear.
Re: Twin Miks on 838 [Re: wbabojo] #737670
06/04/18 7:47 pm
06/04/18 7:47 pm
Joined: Oct 2001
Posts: 247
Monclova
S
sloppyoil Offline
BritBike Forum member
sloppyoil  Offline
BritBike Forum member
S
Joined: Oct 2001
Posts: 247
Monclova
sounds good, but youll need to take the carbs apart to see whats inside, unless you know, to set up a baseline to start the jetting procedure. I can only assume that you had them on a BSA that was a stock 650, now you have modified a bit and having problems. until you know what is inside you wont be able to change it up. If it has p0's in it you may now be lean in the mid??? Good luck.

Re: Twin Miks on 838 [Re: wbabojo] #738696
06/14/18 7:15 am
06/14/18 7:15 am
Joined: Oct 2008
Posts: 5,076
Gnashville
DavidP Offline

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DavidP  Offline

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Joined: Oct 2008
Posts: 5,076
Gnashville
P0 !?
I'm running P4s on a .060 over A65.
As mentioned, you also need to be certain of the correct idle jets and slides.
I'm running 25 idle jets and my screws end up about 1.7 turns out. But that's with Uni foam filters and proper silencers.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
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Re: Twin Miks on 838 [Re: wbabojo] #738971
06/17/18 9:46 am
06/17/18 9:46 am
Joined: Jun 2002
Posts: 204
Ipswich England
wbabojo Offline OP
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wbabojo  Offline OP
BritBike Forum member
Joined: Jun 2002
Posts: 204
Ipswich England
Okay, here's what I have: A pair of VM30's (Left Hand Idle).

Slides 2.5
Main Jet 220
Pilot .25
Air Jet 2.0
Needle Jet 159/P-2
Needles 6DH3
Needle Position 4
Idle Screw turns out 1.5


Last edited by wbabojo; 06/17/18 1:37 pm. Reason: More info

Gavin
You can't make a silk purse from a sow's ear.
Re: Twin Miks on 838 [Re: wbabojo] #738989
06/17/18 3:20 pm
06/17/18 3:20 pm
Joined: Dec 2013
Posts: 4,106
ohio, usa
kevin roberts Offline
fefsa
kevin roberts  Offline
fefsa
Joined: Dec 2013
Posts: 4,106
ohio, usa
on triumphs, i've been able to get more or less identical results running 159-P2 with 6DH3 and 159-P4 with 6DH2.

the one time i tested 159-P0 in a 750 i tried to open the throttle one time and came back. they were way too lean for what i was running.

25 pilots may be too lean for an 838, even with 30mm. i use 35s on a 750 with 34mm, 25s on the same bike with 32mm.

check those enricheners.


i have no idea what i'm doing.

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