I need some answers here!

13 replies to this topic
  • Polar_Bear

Posted June 10, 2002 - 02:43 PM


K, I ride a 426 (obviously), it is an 01. I ride it a lot. At least once a week, sometimes 3! Well my motorcycle doesnt have any compression anymore when it is cold and it is really hard to start (not hard to kick). But once I start it and it warms up, the compression comes back and it is easy to start again. But whenever it is cold there is no compression all over again and it is hard as hell to start. SO>>> Do I need a new top end, or just rings?
>>>>> Is there something wrong with my valves?
Let me know!

  • thumperguy426

Posted June 10, 2002 - 06:16 PM


I'm not completely sure this is the problem but when i first got my 426 i made the mistke of pulling in the compression release on the exhuast stroke so when i would push down on the compression stroke the would be no compression, and i thought i really screwed things up, but i was just screwed up (all of that two smoke exhuast from when i rode 'em) Hope i helped.

  • Polar_Bear

Posted June 10, 2002 - 06:24 PM


nope. I'm not even touching the compression release. Come on guys I know what I'm doing.
Please give me something to work with here!

  • OZZY

Posted June 10, 2002 - 07:09 PM



  • YZ400Court

Posted June 10, 2002 - 07:14 PM


Sounds like you need to find someone with a leakdown tester. It will tell you where the leak is, rings or valves. Have you checked the valve clearance. It will be way big if you bent a valve, and way small(none) if one has beat itself into the head.

  • Mark_Cantrell

Posted June 11, 2002 - 07:17 AM


Don't bother with a leakdown tester. Not one 426F or 250F in fifty could pass a leakdown test. Try this, roll to the compression stroke and instead of pulling in the decomp lever, just stand on the kickstarter. Yeah, I thought so. The heads on these things are static seives. They work fine at speed though.

If you can find the definitive problem, you'll make many of us out here very happy.

Good luck,

  • Polar_Bear

Posted June 11, 2002 - 07:24 PM


Sounds to me like im just going to have to take it apart and see, and since it is already apart I might as well replace the rings and gaskets. Is there anyone out there who would know what to do?

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  • freestyle111

Posted June 11, 2002 - 10:29 PM


its probably cabon build up on valves.the carbon wont let valve seal properly or close all the way.you can pulling off headpipe and spraying some oven cleaner inside exhaust port on head.let it sit for about 5 min. then get small brush scrub inside port.then use air compressor to blow out all oven cleaner.next to get all oven cleaner out of head spray brake cleaner inside port then blow it out with air,repeat but spray wd40 2 or 3 times instead of brake cleaner you want to make sure inside port is clean.make sure engine is at TDC before you spray any oven cleaner inside.that way valves are closed and it cant get into cylinder.

[ June 12, 2002: Message edited by: freestyle111 ]

  • Mark_Cantrell

Posted June 12, 2002 - 03:42 AM


Taking it apart may not help. I lost compression one day and it came back. Lost it again months later pulled the head. Intake valves had coral like carbon deposits around inside of face. Thought I had it, cleaned them up and it still leaks through. sickbird has more experience with them.

Good luck,

  • Vanilla_Gorilla

Posted June 12, 2002 - 10:18 AM


WHOA WHOA WHOA!!!! who the hell says that a yz426 wouldnt pass a leakdown test? BULLSHIZ!!!!!! i can stand on my kickstart lever for 30 seconds and the engine wont turn over, cold or hot, and i weigh 225lbs. and your problem is definately int he valves. after a few months of hard riding, the valves must be adjusted. also, if you ride it alot, there may be some carbonkeeping the valve(s) from seating completely unless it turns over at great speed, or you may just have sticky valves. I would pull the head and do a valve overhaul if things dont look like they r fine. check for valve clearance.

  • JSTheJack

Posted June 12, 2002 - 10:56 AM


I would bet it's the standard 2 smoke problem when a bike won't start....worn rings. I recall something like spraying WD-40 or squirting some oil (a small amount) into the combustion chamber. If it fires up, you've got worn rings and the oil helped seal them.

You can rig up your own leak down tester to test the valves. Some guys have just put in a compression tester in the plug hole and cranked the bike over (in this case kick it over many times) and listened for an air leak. I've never tried this approach, but it is said to work for leaky a combustion chamber. Oh, make sure you've go the throttle WFO when you kick-it-over.

Since these things run, and we ride them, like a 2 smoke, the rings would be a good place to start. Let us know what you find out.

Thought: Even if you're staying away from the compression release, could it be hung open some how?

[ June 12, 2002: Message edited by: JSTheJack ]

  • PMK

Posted June 12, 2002 - 11:40 AM


I'm curious if anyone that has had a loss of compression stores their bike with the piston at TDC on compression. If not the valves will remain open and could corrode the stems causing them to stick, even more so if leaded fuel is used.

If it were my bike I'd try storing it on TDC after I rode and see if the problem doesn't disappear before I tore it apart. Just another idea, and having had these motors apart, they aren't hard to work with, just different.


  • Vanilla_Gorilla

Posted June 12, 2002 - 06:16 PM


GUYS!!!!!! its not the rings! If the rings were worn, he would not have compression when the bike is warm. YEs the rings expand under heat but in turn, so does the cylinder, thus keeping the wear exactly the same. your problem definately lies in the valves, and PMK is dead-on about the storage method, this engine should be stored at TDC right betweent he compression and powerstroke. Just as if your starting it, but after you use the compression release and move the lever an inch, STOP!!!!!!!, its also a good idea to idle it for 20 seocnds with the gas off, then pull the hotstart and let it idle for 10 more seconds. this heats up the plug and lessens chances of plug fouling.

  • Polar_Bear

Posted June 13, 2002 - 02:56 PM


Well, it sounds like it is the valves. My bike even when it was new did not pass a leak down test, cause I weigh 220 and when a stand on the kick starter it doesnt hold. it takes 5 or 10 seconds but after that it slips out of compression. It looks like I will fix the valve problem and since it is already apart it wont hurt to put new rings in it. Thanks for the reply's ya'll!
Polar Bear

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