Hello all,

I have a Mikuni power jet kit installed on my TM38 flatslide carb and Mikuni recommends that original main jet should be reduced by 25% and the reduction will become the size of the power jet.

So in my case my bike is currently using a #380 main jet so i trimmed it back by 25% which now #95 will become the size of the power jet however this is a conversion from VM36 roundslide to TM flatslide with power jet kit so i started off in a richer side by installing a #320 main and a 97.5 power jet then go from there..

If the engine ever shows a rich/lean symptom which most likely it's gonna happen..should i be making the adjustment on the main jet first and leave the power jet alone until i have find a suitable main jet for it or should i be making changes on both simultaneously using the aforementioned Mikuni's formula? and for the future changing condition, should i only make changes on the main jet, power jet or both?

Best Regards,
Jack

Don't know the answer but i recall an IT175 i raced new in 1980 had a power jet carb. Never altered it--but-- i see looking at Babbits online that the "80 IT175 gas a 200 210 220 main & 82.5 power jet. Then the "81 with no power jet still has a 200 210 220 so i don't know sorry. Keen to hear your outcome though. What are you running it on?. I measured my carb off my 1990 RMX250 recently & is a 38mm flat slide, [TM38 think it is]. No power jet though. looks huge & could suck in low flying ducks.

It's been a long time... If I remember correctly the power jet affects things more near full throttle...

So say you're lean from 1/2 to 3/4 but then fine from 3/4 to full you would go up on the main and down on the power jet the same amount you went up on the main... if that makes sense.

That makes sense to me. I will adjust the powerjet accordingly.

Right now i have a piece tape with markings for the throttle position so i can see which part needs adjusting.

It's for my IT250K since i have a brand new unused TM38 that i bought a while back with the power jet kit fitted and when it fitted like an OEM carburetor when i test fitted it on the machine so i thought to myself why not give it a try .