yz250 won't idle, runs great

[cheeze433]

Hey,
I have a 2003 YZ250. The bike has never had any issues. I was riding the other day and when I was slowing down or holding the clutch in, I could hear the exhaust didn't sound right. Instead of fast, crisp sounds, it was slower and appeared to have a bogging sound. When giving it throttle, it would bog for a split second and then clear up. When on the gas, it screamed. Also, if I stopped and idled, the bike would sound like it was bogging again, and would die. However, if I pulled the choke on, it idled great. I tried changing the spark plug, nothing changed. The air filter was dirty, so I cleaned it and also took the carb off and sprayed it with cleaner, although it looked good to begin with. Put it together, same result. Any suggestions?? Very frustrated!

 

[_JOE_]

How many hours on the top end? What kind of maintenance schedule do you follow?

 

[julien_d]

Take the air screw out a turn or so.

 

[cheeze433]

Actually, I have no idea how many hours is on the top end. I have had the bike for three years, didn't ride that much until recently. I have never touched anything on the bike. I just don't understand why it runs great until I'm slowing down into a corner or stopping. Just doesn't sound right.

 

[_JOE_]

Sounds like the compression may be getting low. How does it start? Could also be lean on the pilot circuit but that usually makes a bike really hard to start, especially when cold.

 

[Ouellette]

that could be the issue the bike is jetted correct as well?

 

[cheeze433]

It starts up on 1 or 2 kicks. I guess if the compression is getting low, I've got my use out of it. Like I said, I've never touched the top end since I've had it.

 

[whenfoxforks-ruled]

Where is the air screw best adjusted at?

 

[cheeze433]

Good question actually. I have not touched the air screw since buying the bike. It has always ran unbelievably well. Still does, just won't idle right. Where should the air screw be set at? I can check it. Also, I took the silencer apart. Packing was soaked with black oil. I run 32:1. Is this normal?

 

[_JOE_]

Since it's been a long time since it was serviced I would start by doing a leak down test then if all is sealed down low go ahead and freshen up the top end. While it's apart SOAK the carb (only the metal parts) in one of those tubs of solvent you can get at the auto parts store. Check for crankshaft end play. Inspect the reeds while you're at it. When you get it running go ahead and jet it. Once you check off all those things it should be running better than new.

 

[Uchytil]

Clean the pilot jet.

 

[Ol'89r]

Clean the pilot jet.

Bingo! We have a winner. ;)

 

[cheeze433]

Thanks for all of the great info. I went to take the carb off of the bike a little bit ago. There are two philips head screws on the the top that hold down the throttle cable. One of them has a stripped out head, must be from original owner. I'll have to drill it out to remove it. Since I've never torn a carb apart, do I have to get that part off to get to the pilot jet or can I get it from the bottom? Let me know. Thanks.

 

[Ol'89r]

You can access your pilot jet from the bottom. Remove the four screws that hold the float bowl and remove the float bowl. Look at the bottom of the carb. There will be a big jet in the middle and a tiny jet down in a hole right next to it. The tiny jet is the pilot jet. Remove all the jets and make sure you can see through them. Remove the air screw and blow air through the orfice. Air should come out the pilot jet hole and the little hole in the throat of the carb. If it doesn't, soak the carb in a good carb cleaner and blow it out.

Make sure you use a good quality screwdriver tip that fits the head and it will save your screws from stripping the heads out.

 

[slodad]

... One of them has a stripped out head, must be from original owner. I'll have to drill it out to remove it. Since I've never torn a carb apart, do I have to get that part off to get to the pilot jet or can I get it from the bottom? Let me know. Thanks.

You can probably use some small vicegrips to remove the screw. The heads are pretty soft and the vicegrips will bite into it well enough to loosen it.

 

[cheeze433]

Thanks a lot guys. I'm going to try to work on this thing today. All the info is very much appreciated!