42mm Carb Long and Short Idle

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42mm Carb Long and Short Idle

Postby Kern Family Racing » Tue Nov 20, 2018 10:19 pm

New to 42mm carburetors. What is the difference between the long and short idle adjustment? Is it more like course and fine adjustment?
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Re: 42mm Carb Long and Short Idle

Postby WILD BILL » Wed Nov 21, 2018 7:06 am

Never heard those trerms.

Unless you are referring to the idle screw up on top and the idle mixture screw down on the header side of the carb.
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Re: 42mm Carb Long and Short Idle

Postby Kern Family Racing » Thu Nov 22, 2018 3:13 pm

Then that must be the idle mixture screw, but I had not seen an adjustment like that. I assume it has a better adjustment than the 33mm to control head temp without changing pilots? Any tuning tips?
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Re: 42mm Carb Long and Short Idle

Postby dbbubba01 » Wed Nov 28, 2018 11:45 am

With an alcohol and race prepped 42mm Mikuni all air bleeds are usually blocked off and the IDLE MIXTURE is adjusted with a screwdriver.
The IDLE MIXTURE is the easiest way to set the IDLE TEMP as long as the IDLE JET is correct.
The idle speed is adjusted by the finger adjustable screw that moves the throttle cam and butterfly.
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Re: 42mm Carb Long and Short Idle

Postby Kern Family Racing » Mon Dec 03, 2018 7:50 pm

I looked and you are correct, the idle jet is plugged and I have an adjustment on the left side(looking at the back of the car) for idle mixture. I assume I don’t have to touch the main jet very often and just adjust with air bleed?
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Re: 42mm Carb Long and Short Idle

Postby WILD BILL » Mon Dec 03, 2018 10:42 pm

Both my 42's and most of the ones I've seen have a plug in the main jet air bleed location and no air bleed at all in the pilot location.


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