FYI on jetting YZ426F

When I bought my new 426 I put on an FMF PCIV s.a. on it. I live at 5000 feet, the dealer told me they had jetted it for this altitude #158 main, well it didn't run for s!!t with that jet, I actually was lean fouling plugs. It wouldn't start for jack either. I ended up with a #168 main (SEA LEVEL)!! Now it starts second kick every time and doesn't backfire! No other adjustments were made to the carb! Woo Hooo!

My first reaction is "don't ever listen to your dealer."

My second is "you are too rich on pilot and clip position."

Changing the main on these bikes doesn't really accomplish much from a seat-of-the-pants perspective relative to pilot, needle and clip position.

I ride at about 4k ft., but it is a little warmer (and drier) down here. So here is my jetting for future reference if you want to fool with your jetting some more:

160 main

40 pilot

85 pilot air jet (Sudco, 800-998-3529, PNs 021-230 & 021-235, about fifteen bucks)

EKP needle (PN: 5JG-14916-EP) on clip # 3

1.5 out on idle mix

Hope this helps.

Hey YZBilly;

Very interesting for sure. I think Hick is correct for sure on the first point, and I think he's accurate on the second point too. I run a 158MJ up in the hills, anywhere from 8K to 14K and haven't experienced any real problems. Bike runs good all around. I used to switch back and forth from the 158 in the high country to a 160 when riding down around Boulder, but this summer with the higher temps I've had no problem running the 158 down here. Now, come this fall, the cooler temps will most likely wreak havoc on my jetting as it usually does, still need to work that out.

Dodger :):D

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