bogging and starting issues

I am trying to work the bugs out of a 2001 YZ250F. Since my friend has owned it it has always been a bear to start (compared to other 250F's). I have taken the carb apart and cleaned it along with re-sealing the airbox (just for piece of mind). After putting it all back together it still doesnt want to start and the few times I do get it to start it still bogs. I have tried playing with the air screw and going one up and down on the main and pilot jets. It has a 175 main and 45 pilot now. (tried a 178 main and 48 pilot also). Should I be checking the valves next? I am not sure how many hours are on it, he bought it used.


Geez that thing seems like it's jetted way too rich. Bogging is a sure sign it's too rich. Check out the jetting in my signature. My bike starts like a dream and runs like a scalded ape. I had the pilot circuit just a little richer and it would foul plugs every other week the first thing in the morning. It wouldn't hurt to check valve clearance but it's probably not the reason it's running badly.

Got it. Spark plug cab had a bad connection. Now I can work on the jetting.

See! I knew it was the spark plug cap! :)

On my 'ol '01 YZ250F I used a 38 or 40 Pilot jet and a 165, 168 or 170 main jet. Depending on temperature and elevation.

Yea, The smallest pilot I have is a 42. I need at least a 40 or one smaller. Wont idle unless I hold the choke out a little bit. Gota make a run to the shop tomorrow.

Ok, put in a 38 and I am still getting the same symptoms. I have used a pilot from 38 all the way up to a 55. It simply will not idle without the choke being held out a little bit. If I put the choke in and keep it running with the throttle it backfires and pops. Anyone else have ideas?


Check out this link for info on how to adjust the fuel screw and decide what pilot is required.

Rick's Fuel Screw / Pilot jet information

Also, I've heard that the slide being upside down can cause some of your issues. You might want to check that too.

Sure enough I put the plate on the engine side of the slide in upside down. Wasnt able to start it (too late at night) but I have a feeling it will run fine. Thanx for the tip.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now