Wr426 Wil Only Run On Choke

9 replies to this topic
  • uktrailrides

Posted October 10, 2007 - 12:09 PM


Hi I Have A Problem With A 2002 Wr426 In That It Will Only Run And Start On Choke Have Tried All The Normall Idears Clean Car Even Put A New Piston In All Looks Ok Has A Fmf Pipe When Starting On Choke It Starts Fine Runs For A Fee Seconds Pops Back As To Lean Then Dies This Will Do This A Few Times Then When It Keeps Running It Will Only Run Above Fast Tick Over
Have Changd The Jets Checked Valves All With No Luck Has Any One Come Across This Before This Bike Was Brought By A Novice And Was Riped Off So Just Tryingto Give A Helping Hand

  • luv2ride307

Posted October 10, 2007 - 12:16 PM


Well I have the same bike and never had that problem..... good luck though

  • kevin1209

Posted October 10, 2007 - 12:28 PM


I had the same problem with my '98 WR400. I cleaned the carb jets and flushed it out. I also bought a cheap in-line fuel filter from the local auto parts store and installed it on the fuel line between the tank and the carb. I added a little high octane additive to the gas tank and started it up. It still wanted to die for a while. I just kept kept the RPMs up and feathered the throttle. It took about 15-20 minutes of riding around with the bog in the engine, then it quit. It hasn't done it since.

  • maxtherat

Posted October 10, 2007 - 04:34 PM


New piston??? Check cam timing is correct, pilot jet is clear, and check fuel screw.

  • CAlmride

Posted October 10, 2007 - 05:24 PM


Blew air through all the air passages and jets in the carb?
If I'm not mistaken the choke on the FCR carbs richens the starting circuit. The hot start would lean the carb, have you checked the condition of the hot start plunger? I have a thumb lever for the hot start mounted on the handle bars and sometimes the plunger gums up and is hard to operate.
What does "It Will Only Run Above Fast Tick Over" mean?

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  • Team_Oatmeal_Pie

Posted October 11, 2007 - 08:34 PM


Sounds like plugged pilot jet, make sure after cleaning the carb you dumped the gas tank and take a flash light to look inside the tank to see if dreaded brown scum is growing inside. I had same issue but didnt dump the gas and would get a clean running engine after cleaning it, then few days later when going for a ride it was back to not running at idle with out choke and/or at least 1/4 throttle

  • K9King42

Posted October 11, 2007 - 08:47 PM


You might want to check your hot start. I have a 2001 yz426 with the hot start right on the carb and havn't had any of those problems. My 2003 yz250f had the thumb hot start with the insert into the carb being threaded plastic. I had a similar carb problem with my 2003 yz250f and it was these plastic threads on the insert that threaded into the carb that were worn and messing with my the airflow and carbueration of the motor. I had my idle screw turned up so high that I could literaly idle up a hill in first, but when I tried to turn the idle down, I couldn't keep the bike running.

I found out that the worn plastic threads on the hot start insert into the carb were allowing more air into the carb and causing the problem. Replacing the hot start plastic/threaded piece solved my problem. I don't know what style of hot start you have on your 02 426, but you might want to check and maybe replace that piece.


Buy and new WR 450 and call it a day!

  • steve10391

Posted October 12, 2007 - 08:57 PM


I would completely disassemble the carb and soak it in Chemdip Carb cleaner. You can find Chemdip at most auto parts stores. Its in a 1 gallon can. Let it soak for at least 1 hour. Sometimes the jets and passages will look clean but they could have a layer of varnish that will not come off just by just blowing air thru them. Do not put anything rubber in the cleaner. If you have a service manual check the jet sizes and float level. Should fix it right up.

  • antigrav

Posted October 13, 2007 - 08:49 PM


first off check your GAS!!!!!!!!!!!!!. I had this exact thing happen cleaned the carb twice, still happened..... finally changed gas and added some Sea Foam carb cleaner in gas ran for about 20 minutes and has run great since. I tore my hair out for a week and it was just gas and some Sea Foam which I got the idea from street bike site when I did a google search.

  • WR_Dave

Posted October 14, 2007 - 08:08 AM


If it needs the choke to stay running then it would seem to be very lean without the choke on. You say that you changed the piston, so the engine has been apart, while it was apart did you check to make sure there were no holes or tears in the intake boot. Sounds like the engine is getting air from somewhere other than the carb. I had a friends 2 stroke doing the same thing and it was a crankshaft seal that was the problem, shouldn't effect a 4 stroke that much though. Good Luck with your search and let us know what you find. :crazy: WR Dave.


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