Jetting/starting problems.

hello, I am having trouble with my 2000 yz 250 starting.

alittle background- 230psi cranking compression, 0 air leaks, ride mx 1500ft elevation, temps vary from 60 to 80 currently.

engine was rebuilt about 20 hours ago, new everything.

Jetting- 175main, 45 pilot, 2nd clip stock needle, air screw varies, stock #7 slide.

The plug looks good.

When I start it for the first time of the day it never wants to start. It fires and dies, sputtering out. If I use the choke it starts easier, but nothing like it used to. I have to hold the throttle cracked until it warms up completely before it will idle.

The rest of the day it struggles but if I crack the throttle slightly it starts 1-2 kicks.

I just switched to the 45 pilot from a 48, the idle seemed better with the 45.

I also put in new reeds, fuel inlet needle and fresh packing.

The bike started doing this around ten hours ago, before that it was a one kick bike.

Any help would be greatly appreciated, thanks,


Not that I am much help, but if it started 10 hours ago, and you have only 20 hours after a rebuild, how did you break in the engine for the 1st ten hours?

Depends on the break in procedure:smirk:

I did two heat cycles at home. Loaded up and did another at the track. Let it warm up around 20 minutes then rode it like normal. I have done many top ends and this has proven to work well for me.

I tried dialing in my air screw last night. When the bike is started I have to hold the throttle cracked for around 5-10 minutes until it is completely warmed up before it will idle. Once Idling, I found best idle around 3 turns out, so I need a 42 pilot.

But this seems to far fetched to be the issue. The pilot should be "close enough" to allow proper starting. Being that it is on the rich side, theoretically it should help starting.

Another note. When leaning the bike over to the side until gas pours out, pulling the choke up, it starts 1-2 kicks. But still sputters and runs bad. I have the throttle cracked when starting it, and if I let off the throttle it dies. I can not determine if it is loading up or is a lean condition.

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