Mikuni jetting questions

[Ken Ritter]

Hi, I have 2000 dyna lowrider with a Mikuni HSR42. S&S air cleaner and Vans Hines exhaust. It seems I can back out the air/fuel mixture screw all the way and it has no affect. Seems to pop in the exhaust on deceleration also. I see different suggestions for jet sizes on various message boards. . I am interested in combinations of jetting that folks have found for a similar setup that work well.

 

[Breeze3at]

The best advice I can give is to buy a Sudco Mikuni tuning manual. They are not expensive and will teach you how each circuit works.
https://www.google.com/search?channel=tus5&client=firefox-b-1-d&q=sudco+mikuni+tuning+

 

[dolt]

Agree with Breeze's suggestion on the tuning manual; tuning either the CV or the Mik can be frustrating.

First check for intake and/or exhaust leaks; both can cause decel popping.

Stage 1 configuration and the 42 Mik is jetted pretty close for that configuration in fact, out of the box, the 42 Mik is jetted a tad rich. You have leaned it out a bit with hi-flow intake and exhaust, no major jet changes for a Stage I configuration should be necessary. . S lot of tuner set the A/F at about 1.5 turns our but not at curb idle, try setting it at 1/8 throttle.

Whatever you do, make one change at a time and keep notes on the process. If you have access to a dyno and a competent tuner,
buy some dyno time for some pulls so you can see AFR at idle, partial and WOT; that will tell you where to make the changes. I am a CV buy myself and have found that best results always come from using OEM parts, stay away from the aftermarket jetting kits.