Bike:2001 YZ250 stock engine , stock pipe , FMF Q arrestor Me: trail rider some fast and a lot of slow stuff sea level to 2000 ft terain central coast Cali.

Would like a opinion on my jetting please. I bought this bike a year ago and it runs very well but I thought I could here searing noise similar to a lean condition on full throttle. So I am doing a top-end just for service. It had a Pro-x piston and I am going stock OEM. I noticed a #175 main jet, the book said #178. Also the clip was on 2 slot The piston and cylinder look great and dome black and oily if anything along with the plug, but never foul`s.

Should I just leave this alone?

Thank you

Andy

If you ride the bike hard as hell better to go higher. No harm done with a little richer jetting.

pismowr, on 08 February 2012 - 08:01 AM, said:

Yes its ok - dont't change the main
try the clip on the 3 slot

dmikel, on 08 February 2012 - 11:45 AM, said:

I think it really depends on what fuel you're running and how you ride.

With pump premium, I would burn down my engine running a 175. With good fuel like race gas, or a mix of AV & pump or race & pump, a 175 is great.
In the summer, 175 might be right on the edge with pump. It was always too lean for my 2002 when I was living in So-Cal.

Riding style makes a big difference though. I'm generally running mid-top rpm on MX tracks. In tight trails, things are much different.

3 on the clip with the stock needle is too rich, especially when it gets hot, or you're at the higher elevations.
If you need a little more fuel in the lower/mid, try the 2007+ stock needle. Yours should be N3EJ, the new one is N3EW, it's a touch richer initally. They did that for the pump gas.

Good day Andy.

What's your temp and humidity out there?

My 08 is jetted at 172 main, N3EJ needle at 3rd-clip, premix 32 : 1 ratio 100-octane gasoline and Motul 800 2T, stock pipe.

Temperature here is between plus 70F to 100F and it is very humid. The trail sites we frequent here are around 550 to 650 metres above sea level (1800 ft to 2100 ft). But there are trail sites far north that are located at 1500 to 2000 metres above sea level.

Anyway, without further ado, here's a generic guide for you sir....

joshua_inigo, on 04 February 2012 - 01:17 AM, said:

Thanks for all the replies by the way.

This brings up a good point about the fuel, basically it sucks around here and probably all over(pump gas that is and 91 at best). I looked in the manual and it calls for WAY over the octane rating I have been feeding my poor YZ. I feel sorry fo the poor guy now, and need to treat it to some good stuff, but dont want it to choke and go into cardiac arrest.
I have been running 40.1 mix with Blenzall and it smokes allot when I start it and allot on the tight trails(idling allot) which helps keep down the bugs.Should I be at 32? and better mix? I wonder. To be honest I run blenzall since it smells good LOL

Joshua, we have similar temps as you but not humid. Thank you beautifull lady for the very handy chart.
Andy

One thing you might check is with the fuel distributors in your area, I can go to a local distributor and purchase 100 to 110 octane, it's spendy but much more reasonable than race fuel.

joshua_inigo, on 09 February 2012 - 12:30 AM, said:

I would like to spank her personnaly for the guide

BRM, on 10 February 2012 - 12:00 AM, said:

She sure looks very attractive. In person, she's just mind-blowing!

Had to control my adolescent instincts though

mtdirtbag, on 09 February 2012 - 09:10 AM, said:

Gonna check on that today thanks

I had another killer day on the trails with some buddies, all I did was move the clip to the third groove on the needle. Same 175 main and Redline pre-mix at 40.1. It started right up cold which it hasnt done in a long time, probably starving for fuel being too lean cold. I still have allot of smoke, not terrible but my pipe is still the stocker I just removed the dents and silencer needs repacking I bet, maybe they are just oily inside. I need to pull the plug and check it out next.
But no more shearing noise on the top end, and more power than I will ever need

Happy days thanks for input everyone.

that's good news indeed, good jetting beats a bad jetting anyway.