My bike has been running worse and worse over the last eight or ten months.  It runs ok when it is cold or luke warm, but when it gets to normal operating temp won't idle. My idle screw is all the way in and it still stalls.  it loads up in lower rpms and runs super rich.  My piston and rings are still like new. I changed my right side crank seal and set my float height and a fresh plug and cleaned my carb. Now my plug is almost white and it still loads up and stalls when i go down hill and then when im back on flat ground it take a few seconds to clean back out and run.  it also surges on the bottom and is really hard to ride. Now my air screw is 3 - 4 turns out and i cantake it right out and it run alot better, so it appears i need a leaner pilot but it is already running lean so that would make it worse

anyone have any ideas?

Sounds like it could be ignition related, could be a dodgy coil or stator. They tend to go south as the bike heats up. Try closing the plug gap and see if it makes any difference.

khooge, on 26 June 2012 - 03:36 PM, said:

At what altitude and temps are you riding? What main and pilot are you now using?

Edited by dzamo, 26 June 2012 - 03:50 PM.

I ride at about 1200' and my pilot is a 48 and my main is 172.  My jetting has not been changed in three years and is usually spot on

khooge, on 26 June 2012 - 03:36 PM, said:

8 to 10 month for me is about 100 hours, how many hours have you done with the piston - Cylinder? That apart have you had a look if your crank bearings are still OK and have no up and down play? If your jetting hasn't changed in 3 years, has your riding style changed?

I run the a JD needle in 4rth and on the other bike the oem needle in 3rtd, both bikes have a larger main than yours. I ride a stretch of a mile to get to the off road area I practise in, just enough to melt a piston with a main at 170/172 if I'm not careful.

my main is actually a 178.  My crank bearings are good and my compression is at 240psi.  I have added a rekluse  autoclutch and i ride  faster now than ever. I am going to check my left side crank seal tonight.

I rode my bike tonight and it bogs and almost stalls if i hold it wide open.  so I checked out my ignition system and my primary coil has too much resitance it should be from .20 to .30 and mine is between .30 and .40 is this enough to give my bike these symptoms?

Could be, anyone living close to you who runs a yz 250 able to lend it to you just to see if that's the fault?

khooge, on 27 June 2012 - 09:39 PM, said:

Yes it is... mine was over by a smaller margin than that and it ran like crap above 1/2 throttle. Swapped the plug boot and it runs perfect again.

This sound anything like what your bike is doing?



The throttle was being held wide open in both vids...

IYa that sounds the same. mine is a bit worse though. I will borrow a coil and see what happens

Let us know the results... you can usually find them extremely cheap online if it turns out to be the issue.

My main Jet had fallen out thats why it was bogging on top.  It runs like it is rich on the bottom and when I go downhill it still wants to stall.  My midrange is really peaky and lurchy.  Could that be from a weak spark?

I tried a new coil today.  still runs poorly.  I borrowed a carb and tps from a buddy and will try that.

I have tried everything!!  I just tried a different carb and tps, still no diff.  Could it be a con rod bearing?  Or a sticky power valve?