So I've got this issue

Had a 36mm vm mikuni fitted but was running out of power at about 5500-6000rpm so I'm thinking its a carb issue associated with the limitations of a single mikuni. Also after warm up of say 15 mins it would misfire a bit in that range so definately thinking it may be a fuel supply issue.
So.... I fit a pair of js34mm flatslide carbs I have lying around and bottom end up to 4000rpm is heaps more torquey but then nothing. Just wont rev beyond 5000rpm at very best but up to there it's really sharp. Can really feel the difference between the single mikuni and the 34mm flatslides.
What is going on here. I've timed the Boyer at 32adv @ 5000rpm with the mikuni just prior to fiting the flatslides.
Is it still requiring more advance???
If so I can't remember if anticlockwise retards or advances the ignition timing.
Any advice would be greatly appreciated
Cheers
DKT

Dkt26 said:

I can't remember if anticlockwise retards or advances the ignition timing.

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The Commando cam and Boyer pickup rotate anticlockwise when viewed from the R/H side, so turning the plate in the same direction retards the ignition.

Duh no way on God's Grey roads that a 36 mm single can't feed more mixture flow than even an 850 can swallow beyond redline so your rpm limits is a tuning or fuel feed issue not carb size limiting flow.

hobot said:

Duh no way on God's Grey roads that a 36 mm single can't feed more mixture flow than even an 850 can swallow beyond redline so your rpm limits is a tuning or fuel feed issue not carb size limiting flow.

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+1

Oh ok thanks. Is the misfire symptomatic of the battery perhaps being low then.
I'll check everything over this morning and advance the ignition a bit more.

make sure your plug gap is not too wide.

Battery low might be an issue for electronic sparkers at low rpm but I've put lots of miles on Boyer with dead battery or no battery - as long as I kept rpms up near 3000 or more. Its possible the rpm vibe range is affecting a connection or a inside wire break. If float level on low side, so miki pilot air screw turned in past normal to get good idle may not feed enough flow so leans out power down. New Plug chop could sense that. Main jet may just be too small but the throat sure ain't.

your timing is fine

I've timed the Boyer at 32adv @ 5000rpm

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leave it alone

not the problem

Is it possible that cam chain tension is affecting this? Gets worse as heats up.
The nik had 300 main so I am definately thinking its ignition related.
What would be the symptoms of over tight cam chain or belt drive?
Thanks thus far for the input all.
Cheers
DKT

i advanced the ignition a smidge, say 1 mm turn and have addressed the issues reported. this confuses me a bit as with the strobe, i am running 32 advance but the ignition is still retarded too much. Havent strobed the new setting as i have the primary off to run and check belt tension once hot.
also acheived tis positive outcome with points cover off and wires swingin in the breeze.
have now refitted points cover and will check just in case there is some distortion occuring with it fitted.

Snakepit said:

make sure your plug gap is not too wide.

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+1
Your ignition could be overwhelmed. I went through symptoms similar to this with Amals. It turned out to be a marginal coil. Closing the gap a little improved things, but a new coil solved it. I was running a 560 cam and about 10:1 compression.

Your belt primary may have a hard time heating up if you have the cover off. Even then, it takes at least a half an hour. Depends on the ambient temp.

Dkt26 said:

i am running 32 advance but the ignition is still retarded too much.

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and

Dkt26 said:

Havent strobed the new setting as i .................................

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Agree with 1up3down that if your igniton was set as described in your OP it should not be a problem.

I am concerned that you advanced your ignition "a smidge" and then go on to say it "is still retarded too much". If this is a Commando the 31 degrees advanced setting is plenty ample and some opine that is a bit too much.

I suggest you get your ignition sorted out soon.