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1985 GSX-R 750 - replacing the single main air filter with 4 air filters directly on carbs

3.9K views 10 replies 4 participants last post by  Dirk GR75A  
i am running 140 mikuni main jets with aftermarket needles on my 87 model 34mm carbs. be aware that the 86 model carbs are 31mm, so the jetting is different. removing the airbox will make a significant improvement in over all power.

oh wait, you have the OEM rest of the world 1985-1987 750 29mm flatslides, so the jetting will be completely different.
@Dirk GR75A is from Greece so he's got flat slide 29mm carbs like the Canadian bikes. Jetting these carbs is a little tricky. I had mine done on a dyno several times. If you make any changes to the filters or exhaust they get fussy.

Mine had a 97.5 main with the factory pipe but it did have that flat spot around 6500 - 7500 RPM that was a common complaint. When I had it running with a big Yosh race pipe and single K&N in the OEM airbox we went to a 107 main jet. We also raised the needles. I don't know if we went all the way up or just one clip below top.