03' YZ250 cutting out

Hello guys - I do not normally post here but i'm having a helluva time with my YZ250.  Here's the scenario:

 

I've had a recurring problem since i rebuilt it in March, the problem was not there beforehand. (Wiseco crank, rod & main bearings......fresh cylinder plating from US chrome with wiseco piston, all new transmission bearings)  The bike runs great until it hits the pipe for just about one second.  It shuts off which is very similar to holding down the kill switch.  LIfting and re-applying the throttle does nothing.  The bike continues to rev down until rpm's reach 0.  After that it can be re-started and ridden until it hits the pipe for rougly one second....then it's the same scenario.   It can be held wide open in neutral and does not cut out.  I've only tried for 2-3 seconds....scared it's gonna fly apart.

 

Here's what i've changed & inspected:

 

Cleaned carb & electrically checked powerjet solenoid - no change

Replaced ALL wiring, CDI, coil, kill switch - no change

Just replaced stator tonight - no change

Fuel tank petcock is not plugged

Replaced spark plug - no change

Checked carb needle valve - it's working properly

Fuel tank vent is not clogged

Carb vents are not clogged

 

Any Ideas?

 

 

i know you went through the carb but did you check float height

Say recurring...and this was from the rebuild in March...Does this recur and then go away..or has it been this way ever since the rebuild?  It does sound float fuel related but  it should never completely die. It could be something as simple as a bad ground. 

i know you went through the carb but did you check float height

 

Yes float height is good.

 

Say recurring...and this was from the rebuild in March...Does this recur and then go away..or has it been this way ever since the rebuild?  It does sound float fuel related but  it should never completely die. It could be something as simple as a bad ground. 

 

It would go away at times but for the most part I've been dealing with this since March.  I first thought it was a bad kill switch, then a connection on the coil touching the frame.....it's then snowballed into a parts changing fest. 

 

I don't think this is fuel related because the bowl drain supplies way more fuel than this thing can burn in 1 second.  Also - lifting off the throttle does nothing.

 

I've checked the coil and the TPS sensor with a multimeter and it checks out.  Last night I unhooked both of these connections and did not have a problem.  It's hard to say if this was a fix or the problem isn't occurring at the time.  It's tough for me because other than trying it on the road, I have to drive an hour to the nearest track.  I'm wondering if the TPS or powerjet coil is grounding out the stator & shutting down the bike.....

The power jet is fed voltage from the stator so i would be looking at that. Keep us posted on what you find.

I could be wrong, but I think you can run the bike with the powerjet solenoid disconnected.  Might be worth a shot to test it.

I could be wrong, but I think you can run the bike with the powerjet solenoid disconnected.  Might be worth a shot to test it.

 

Yeah i've tried it a few times with it being disconnected.  The bike does not cut out and i cannot tell the difference while the carb is unpluggled.

 

I still have not concluded why the TPS or coil is causing the problem.

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