Vm20 jetting stock 110

T Reds · Apr 12, 2015

I got a brand new mikuni vm20 carb for my ttr110 and have no idea what jets to get. It comes with 22.5pilot and 180 main but I read that is way too rich so I ordered a 17.5 pilot and 115 and 125 Main jets. I put the 17.5 and 115 in and the bike ran OK for awhile until it started to bog bad and eventually died. It ran best with the air screw almost all the way in but it still liked to bog.

Can somebody please give me a good starting point for jets on a stock ttr 110 with just a pro circuit t4 and an opened up airbox. Even if you have a klx with this carb your input is aalso appreciated.

T Reds · Apr 16, 2015

Ls1 · Apr 16, 2015

If it ran best with air screw almost all the way in that means almost no air and all fuel = rich. That means your pilot is way lean and not letting in enough fuel. You need to go to the next bigger pilot jet. You can also richen your situation by lowering the needle clip. this will raise your needle and richen your circuit for 1/4 through 3/4 throttle. If I were you and I had the jets available you do: I would put the 22.5 pilot back in. Set air screw 1 and 1/2 turns out from full closed. Run it and see what it does. If it seems too rich now you can back your air screw out to 2 turns. This will allow more air and lean things up a little. You can also raise the needle clip (lowering needle) to lean the circuit mentioned above. Regardless, I think you are way lean at the moment with 17.5 pilot. Put 22.5 pilot back in. If its too rich and cant be fixed with air screw and needle adjustments - go one or two size pilots smaller than the 22.5.

T Reds · Apr 17, 2015

I put the 22.5 in and it ran best with air screw 2.5 turns out so I've got a 20 pilot on the way. Hopefully that fixes the issue. I pulled the plug and it was dark black. I just wasn't sure whether to go leaner or richer, thanks. I'll post up the results when I get the new jets.

Ls1 · Apr 17, 2015

T Reds said:
I put the 22.5 in and it ran best with air screw 2.5 turns out so I've got a 20 pilot on the way. Hopefully that fixes the issue. I pulled the plug and it was dark black. I just wasn't sure whether to go leaner or richer, thanks. I'll post up the results when I get the new jets.

Yep, with 17.5 u were way lean. With 22.5 you are now rich (hence the dark plug). Once you put the 20 pilot in: Reset your air screw to 1 and 1/2 turns out. If you have to go out more than 2 to 2 & 1/2 turns (leaner) to get it right = your pilot is too rich, you need smaller than 20 pilot. If you have to go less than a turn in (richer) to get it right = your pilot is too lean, you need bigger than 20 pilot. Ideally, when you put the 20 pilot in the bike will be running best with air screw between a turn and two turns out. One other note: When adjusting the air screw, get the motor to full operating temp, turn the air screw slowly from 1 & 1/2 turns clockwise until you hear your idle drop. Note that position. Now turn the screw counter clockwise until you here your idle drop. Note that position. Now position your air screw in between these two positions. This is your optimal position for that given pilot size. This last part is optional: you can mark this last position and double check its position by screwing all the ay in, then back out to where it was. This is to ensure that your final setting is more than one turn and less than 2 and a half turns out. Cheers.

Vm20 jetting stock 110

T Reds

T Reds

Ls1

T Reds

Ls1

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