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Jetting Sanity Check

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2001 YZ125 PC pipe FMF spark arrestor

top end with about ~10 hours

I had a lot of oil running down the back of my silencer after my last few rides. Temps in the 50s maybe low 60s elevation 1500-4000 ft.

Was running:

Main: 460

Pilot Jet: 22.5

Needle:#3 position

Today i tried out the procedure in the jetting sticky to test the pilot jet. I could not get it to idle at all running what i listed above. So i changed the pilot jet to a #20. Now i can get it to idle. Temp about 75 about 200 elevation.

The manual says:

59-77 F

Main: 460

Pilot Jet: 25

Needle: #3 position

86+ F

Main: 450

Pilot Jet: 25

Needle: #3 position

So i am a little concerned about how lean i am on the pilot. But it seems like if i can ge it to idle pretty nicely can't be too off.

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I am sure you did this, but did you adjust your airscrew when playing with the pilots?

Really, i would not be worried. Bikes don't seize from lean pilot jets. I have also had weird jetting come in to play when using a s/a silencer.

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Yes i did. Just seemed strange to be so lean on just the pilot. Just concerned because in the fall i siezed my motor, then i was running main: 450 and pilot: 22.5. I think it was lows 80s high 70s. Don't want to repeat that. Just have never been able to get it really dailed it so far I feel like.

incase anyone wanted the procedure, from the jetting sticky,

Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet.

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