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Vintage British motorcycles circa 1900-1977
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zeero | Tue Feb-14-06 12:38 AM |
Member since Feb 14th 2006
8 posts
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"Single Mikuni setup"
Tue Feb-14-06 02:08 AM by zeero
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Howdi
I have recently purchased a 71 Commando with a single 34mm Mikuni on board.The bikes problem is that it runs too rich on the right cyl to the point of 20-30mins down the motorway its fouled that plug real good(the other side is nowhere near as bad but still on the rich side)I know there could be a number of reasons(and i am a virgin at this)so here's a list of what its installed:
pilot jet - 25
slide - 2.5
needle jet(159) - p4
needle - 6DH3
main jet - 230
air jet - 2
I leaned the needle clip position to 2nd from the top & tried a hotter plug(NGK B6PES) but it still fouls up...???
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MichaelB | Tue Feb-14-06 11:27 AM |
Member since Dec 04th 2002
174 posts
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#1. "RE: Single Mikuni setup"
In response to Reply # 0
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You don't say what ignition you are running. Points, electronic??
Sounds like a weakness on the right side.
It does appear however your combo of P4, 2.5, and 2.0 are giving an overly rich mixture. I would first start with a P0 needle jet and go from there.
My single Mic 750 is long gone but I think it was set up with 3.0 slide, P2 jet, 2.0 air, 25 pilot.
Good luck. Mike
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zeero | Tue Feb-14-06 03:25 PM |
Member since Feb 14th 2006
8 posts
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#3. "RE: Single Mikuni setup"
In response to Reply # 1
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>You don't say what ignition you are running. Points,
>electronic??
>Sounds like a weakness on the right side.
>
>It does appear however your combo of P4, 2.5, and 2.0 are
>giving an overly rich mixture. I would first start with a P0
>needle jet and go from there.
>
>My single Mic 750 is long gone but I think it was set up with
>3.0 slide, P2 jet, 2.0 air, 25 pilot.
>
>Good luck.
Its running the Boyer electronic ign at 31* BTC @ 5000rpm.I replaced the leads & the valve clearances were correct.Thanx for your input i shall try 
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dynodave | Tue Feb-14-06 12:29 PM |
Member since Dec 04th 2002
618 posts
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#2. "RE: Single Mikuni setup"
In response to Reply # 0
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I have seen this same problem posted several times on this forum in the past. In each case the slide cut away was to small. Increasing the cutaway really sweetened up how it ran dramatically.
Yours may be the same but nothing is for certain.
Do a search in the archives and you may find all the details.
Also
There also is a principal called induction port bias which throws a bit more fuel in one side vs. the other. This principle is reported in early BSA's. The flow characteristics of your aftermarket manifold would possibly have influence over this unequal flow distribution.
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zeero | Tue Feb-14-06 03:29 PM |
Member since Feb 14th 2006
8 posts
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#4. "RE: Single Mikuni setup"
In response to Reply # 2
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>I have seen this same problem posted several times on this
>forum in the past. In each case the slide cut away was to
>small. Increasing the cutaway really sweetened up how it ran
>dramatically.
>Yours may be the same but nothing is for certain.
>
>Do a search in the archives and you may find all the
>details.
>
>Also
>There also is a principal called induction port bias which
>throws a bit more fuel in one side vs. the other. This
>principle is reported in early BSA's. The flow characteristics
>of your aftermarket manifold would possibly have influence
>over this unequal flow distribution.
>
>
>
Yeah i did some research through the archives but me head started to fill up too muc 
And yeah i had heard that one side can tend to run richer than the other,are there any wedge shaped manifold gaskets to cure this?
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