2003 CR250 Not running right :(

I've got an 2003 CR250 that is not running properly. 

 

Aftermarket Parts:

 

FMF Fatty Pipe with Powercore 2 Silencer

Keihin 38 mm PWK Airstriker Carb (blue needle in first position, 172 main, 45 pilot) 

Boyesen reeds 

Steahly flywheel weight

 

Here's a little back story...

 

I've been riding the bike with no issues since installing the new parts and it was running great for a few months.

 

I went out to practice at Canyon Motocross and it was working good. I pulled off to take a break.. got back on the track and all of a sudden it starts doing this weird stutter out of nowhere. Like it's bogging down. I pulled off the track.. everything looked good. Got back on and it still did it.

 

I decided to take a look at the RC Valve components and I took the entire top end off and apart. The cylinder was cracked at the exhaust port and the squish zone on the cylinder head was blown away. I rebuilt the top end. New Cylinder, New cylinder head, new piston and rings, new flap valves and a new flap valve shaft. The cables were replaced a few months ago - slack is good. I Installed everything and made sure all the parts moved as they should. Checked the reeds and they looked good. Cleaned out the carburetor. Cleaned the air filter. Been running a 40:1 mix with Castor 927 premix.  Fired the bike back up and its still doing the same sputter. Took it out to the desert and it still did the same thing. It seems that the problem gets worse the longer the bike runs

 

Took it to Canyon again after some float adjustment on the carberetor and its still doing it. Decided to check the RC Valve at the track by taking the cover off and looking at how the valves are opening and closing. Turns out it is not closing properly. It flutters and would stay wide open at idle... So we tested the servo and it didn't seem as strong going in both directions so I replaced the servo motor. Put the new one on the bike and it still stays open at idle and won't close as it should at lower RPMs

 

Next we decided to replace the CDI.. Put a brand new CDI in the bike and fired it up. WOO! the bike seemed to function properly while sitting in the garage. The RC valve seemed to be opening and closing like a champ. Took it out to the track... still getting the same sputter.. Took the RC valve cover off and revved the bike up. For the most part it looked to be functioning properly. At mid-throttle there seems like there is a slight flutter. 

 

So we thought Maybe the flywheel weight is throwing something off? Took off the weight and rode the bike.. Still does it. 

 

I'm lost. There are only a few more parts left to replace before I have almost an entirely new bike. I'm thinking it is an electrical issue purely based off of the fact that this problem started out of nowhere. 

 

Any opinions? Does anyone have a 2003 CR250 they wouldn't mind letting me swap parts to diagnose the problem :p 

Your jetting seems lean, what altitude are you at and when you say 1st position on the needle clip is that the notch on the bottom or the top of the needle (1st position would normally be the notch on the top or closest to the blunt end of the needle which would make your jetting way lean IMO).

If that servo driven power valve is getting power from the stator that is where i would check.

I would look into getting a jd get kit. I just pick one up my self and man what a world of a differance it made.

I would look into getting a jd get kit. I just pick one up my self and man what a world of a differance it made.

 

if you read his post, he is using a JD jet kit.

if you read his post, he is using a JD jet kit.

Yeah I just skimmed through, my bad.

What was the outcome?

The only time I used Castor 927 it seperated and the temp never got below 50*F.

bike would barely run.

What was the outcome?

I love how people come here with questions and then just leave us hanging with no resolution...... :rolleyes:

I love how people come here with questions and then just leave us hanging with no resolution...... :rolleyes:

 

My favorite is when other posters come in and tell him to run a JD jetting kit, without reading that he ALREADY was. Finding good help on the internet is difficult. 

Edited by Blaze45

PS. OP if you are in the PHX you can hit me up anytime to swap parts. I have the exact same bike. I live in Mesa.  

Edited by Blaze45

I PM'd him, it was a bad connection in the wiring harness.

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