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jkv45 · July 12th, 2015, 01:07 PM

Does it just fall flat, or does it stutter and stumble when you get to that range (1/8 to 1/4 open)?

The new Dynojet needles may be off. I would try the stock needles, and then add a shim, then 2, and test again. It's possible they are too lean or too rich for your particular conditions. If you can get a good idle at the correct speed within the 2 to 3 1/2 turns out on the idle mixture screws I would say the pilot jet is correct. I would also sync the carbs.

I was tuning a small 2-stroke street bike that I recently purchased, and it would stumble terribly as I opened the throttle 1/8 to 1/4. It would idle and pull away fine, and pull hard at WOT, but in between it was a mess. I adjusted the clip on the needle up and down all the way without a significant improvement. I decided to get a leaner jet needle ("needle") and it helped, but even at the leanest setting it was still rich. I ended-up getting a leaner needle jet as well - this particular carb (Mikuni flatslide) as a removable needle jet that works with the jet needle to regulate the mid-throttle mixture.

BTW, a Mikuni (Sudco) tech I spoke with said that changing the float height does not effect the mixture - which I always believed it did.

July 12th, 2015, 01:07 PM	#7
jkv45 Rev Limiter Name: Jay Location: WI Join Date: Jul 2013 Motorcycle(s): '06 SV650n, '00 Derbi GPR, '64 CA77 Dream 305, '70 CL450 Scrambler, numerous dirt bikes Posts: A lot. MOTM - Jun '18, Oct '16	Does it just fall flat, or does it stutter and stumble when you get to that range (1/8 to 1/4 open)? The new Dynojet needles may be off. I would try the stock needles, and then add a shim, then 2, and test again. It's possible they are too lean or too rich for your particular conditions. If you can get a good idle at the correct speed within the 2 to 3 1/2 turns out on the idle mixture screws I would say the pilot jet is correct. I would also sync the carbs. I was tuning a small 2-stroke street bike that I recently purchased, and it would stumble terribly as I opened the throttle 1/8 to 1/4. It would idle and pull away fine, and pull hard at WOT, but in between it was a mess. I adjusted the clip on the needle up and down all the way without a significant improvement. I decided to get a leaner jet needle ("needle") and it helped, but even at the leanest setting it was still rich. I ended-up getting a leaner needle jet as well - this particular carb (Mikuni flatslide) as a removable needle jet that works with the jet needle to regulate the mid-throttle mixture. BTW, a Mikuni (Sudco) tech I spoke with said that changing the float height does not effect the mixture - which I always believed it did.