426 Starting Issues

Just had the bike overhauled.. now fowling plugs after one ride then failing to start. The bike shop has played with carb as was leaning out at top end. The mechanic is a very good well respected chap and is a little mistified as to why... now going to play with carb again. It appears that the carb is running to rich?? Any other suggestions out there.

Be certain that you are running a CR8-E, or equivalent heat range plug, or one of the upgrades (iridium, etc.). CR9's will foul.

For some reason the yz's 426 four strokes are a pain to start. It's even more of

a pain when your motor is hot and you stall it. I always ride were there's a hill just

in case I need to bump start it. What I've been doing is turning off the gas at the

petcock and let the motor run some of the gas out of the carb before turning off

and storing the bike. It's all about timing when kicking it over. I make sure the pistons

at top before the big kick. Running high octane gas also helps.

426's start easy when the pilot circuit (idle fuel/air mixture) is set-up properly. Search the forum, you will find a lot of info on this one.

IMO, disregard the previous post, except the part with the piston at TDC (if you don't have an autodecomp. cam).

And what do you do with the fouled plugs? Clean and put them back in? How do you clean them? Don't use steel or brass or any metal brushes !

... disregard the previous post, except the part with the piston at TDC ...

Disregard that part, too. The piston needs to brought brought up against compression, then moved slightly closer to TDC, but not up to or past it.

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_a.mpg

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_b.mpg

426's do start reliably when the plug is in good condition and the carb is correctly adjusted. They are, however, quite fussy about their routine. Also remember that the carb has an accelerator pump, and you squirt gas into the engine every time you twist the throttle. The old two-stroke twist while you kick thing will keep the bike from starting indefinitely.

might help if you post the jetting of the carb. more than likely it is to rich or you have a problem with oil control in the motor (ie something not assembled or seated properly)

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