Mikuni Carburetor Theory and Troubleshooting.

C

cobrafreak

New Member
I was having a weird tuning problem with my Indian's engine. It wouldn't idle at all and such. I did some searching and found this gold mine of a web site:


http://www.iwt.com.au/mikunicarb.htm

It explains how the Mikuni Carbs work, what each adjustment is for, what throttle range for each adjustment is, trouble shooting, etc. This five minute read saved me a lot of money and grief. Book mark this page if you are planning on getting a Honda clone engine and have a Mikuni carb in your future.

My problem was a piece of foreign matter that got into the idle jet channel and it would clog and unclog constantly. Works better than it ever has now.
 
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On a mild 200cc engine we typically use a 125 main jet. The stock main jet in the 22mm Mikuni we sell comes as a 95 or 100. The stock pilot jet is a 15. This works well for about 50% of our customers. The other 50% experience a slight bog off of idle. Installing a 12.5 pilot jet will clear up that bog. We just go ahead and install a 12.5 pilot jet in all of our personal builds. We leave all other setting in the stock position. The air screw is set at 2 1/2 to 3 turns out from the factory which works well. The needle is set right around the middle position from the factory which also works great most of the time. We play with the needle setting to fine tune the low to mid range throttle response.

We get a lot of questions about idle speed when the Mikuni is used. First off, pulling the choke lever up would be the on position. We almost always use the choke to start the engine. The engine will idle higher with the choke lever in the up position (about 2200rpm). This will engage a standard clutch. Once the choke lever is down in the off position the idle will come down. And there is an idle screw which moves the slide up or down to control the idle speed. If you have the idle screw backed all the way out and the idle is still so high it's engaging your clutch then you probably have a vacuum leak. Check the intake gaskets to ensure a proper seal.

We get questions about Mikuni carbs daily. They're actually pretty straight forward after you've played with them for a little while.

Tuning guide
http://www.affordablegokarts.com/carburetor-tuning.php
 
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I finished my 2nd build last weekend and this info proved to be very helpful!

Thanks Guys!!!

-Kirk
 
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