2002 YZ 426 random stalling/starting issues

This isn't a new topic but I'm not seeing any other posts with similar issues: I've been rebuilding my 2002 YZ 426 over the last few months and, until lately, it's been running great. Over the last few weeks, however, it's been starting on the 1st kick, running for maybe a minute and then slowly dying. It will start again after a few more kicks then dies again until eventually it just won't start at all. (Yesterday, however, it ran all day with absolutely no problems?!). Today the same symptoms appeared again. I've checked spark, replaced spark plug, performed leak down test and installed an inline fuel filter. I've also (today) drained the float bowl and replaced the pilot jet. The valves and timing are in spec and engine oil and air filter are both good. Any ideas?

 

If you check it immediately after it dies by shutting the gas off and draining the carb, is there the normal amount of gas in the bowl?

If you check it immediately after it dies by shutting the gas off and draining the carb, is there the normal amount of gas in the bowl?

When it died again yesterday, I kicked for about 15 minutes to see if it would start again, with no luck. Within about another 10 minutes I removed the float bowl to get at the pilot jet and the float bowl was full of gas...  When this same scenario played out a few weeks ago we discovered the pilot jet was clogged. The pilot jet was cleared out and I installed a new in-line fuel filter at that time. It ran great a few days later (which was two days ago, Friday) but then these symptoms reappeared on Sunday. The only thing I did after the Friday ride was: Washed the bike (it was muddy as hell), restarted it (on the 1st kick), and ran it up and down the street, and put it away Friday night. Sunday morning I topped off the gas tank before the ride (gas tank has a brand new vent hose, too), started the bike (again, started on 1st kick), and putted around the staging area to get it warmed up for the ride, and then... no start.

 

Any help from you more experienced guys (and grayracer513) is greatly appreciated as I'm seriously puzzled on this one

Edited by dlediard

You may want to check your gas cap vent and vent tubes on the carb.

Problem solved. After double/triple checking the carb and all vent tubes I finally got a no-spark symptom. I replaced the stator and it fired up on the first kick. New lesson: intermittent spark issues = check the stator!

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