need confirmation main jets 81 750L

[quikvrsixx]

from what i read on the spec page and also by buying a used set of carbs the mains on an 81 gs750L are 112.5. i bought a dynojet kit and it came with 130's and 124's and the recommendation to use the 130's with pods and exhaust. i have been having much difficulty tuning the carbs because it is running so rich. a jump from 112.5 to 130 seems like an awful lot and even with the 124's it is still rich. it seemed that the needles in the kit were so much more pointy than the stock needles they were allowing excess fuel to to by them no matter where you put the needle so i put the oem ones back in and it seemed to help, but are the 124's still too much from 112.5. appreciate any info.

 

[BassCliff]

Hi,

The Mikuni jets and the Dynojet parts do not use the same measuring method for their size designations. Dynojets are measured according to the actual size of the hole in the jet, i.e 130mm diameter. Mikuni jets are labeled according to the flow rate of the part, i.e. 112.5 cc of fuel per minute.

Here's a conversion chart: http://www.4strokes.com/tech/carbjetxover.asp

There is a conversion spreadsheet on my website (Thank you Mr. salty_monk!). The conversion factor between the two is about 0.9375. IOW, multiply the Dynojet size by that number to get the approximate Mikuni size, or divide the Mikuni size by that number to get the Dynojet size.

The 112.5 Mikuni size converts to a ~120 Dynojet. Usually you'll want to go up about 4 sizes with pipes and pods. Four sizes up from Mikuni 112.5 would be 122.5. That number converts to ~130.6667. But if that's too rich, go down a size and test some more, using plug chops or your favorite method. See:http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

The pointy needles are to help richen the midrange. They should have 5 grooves on the top so that you can adjust them up and down to tune that circuit. Moving the needles up is richer, lower is leaner.

I'm hoping someone comes along to check my math. I wouldn't want to steer you wrong.


Thank you for your indulgence,

BassCliff

 

[quikvrsixx]

thanks again, i did not realize the size conversion. makes a lot more sense now. learning something new every day.