Random no compression on wr426 when starting?


2 replies to this topic
  • dchooo

Posted October 27, 2013 - 09:04 PM

#1

So I have a 2002 wr426sm that I finally built up but it's been acting up alot lately. When I go to kick it over WITH the choke on, it will sometimes seem like it has no compression. It will constantly just kick over even after TDC. When I try to kick it over before I turn the choke on, it has compression. Sometimes when I turn the choke on and turn it off and try to kick over the bike, it will continue or kick over past TDC with what it seems like no compression.

 

Once I pull the throttle about a half a turn or more, it finally gets some compression. Once it's heated up it seems to get compression again but usually only when it's cold it has the no compression issue. This issue has started to get worse for the past couple of days.

 

I have a 2004 yz450 exhaust camshaft in the bike and just got done checking the valves. They're all in spec. INT ~.10mm, EX ~.20mm.

 

I also took off the decompression lever because I don't really need it.

 

I'm suspecting it's a bent valve possibly?? Btw, the jetting is perfect on the bike. I took out the plug and it's got that perfect dark-tan color.

 

Let me know what you guys think..


Edited by dchooo, October 27, 2013 - 09:08 PM.


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  • DunmireD001

Posted October 27, 2013 - 11:11 PM

#2

It sounds like your bike has auto decomp cams in it. (Common conversion). On the 2001's and 2002's they came with the decomp lever, but by 04 they done away with the lever and just put auto decomp cams in them because they were tricky to start compared to other dirtbikes... This paved the way for electric start, which is why the 04's were electric start and the 02's weren't but anyways if your bike is starting fine and runs strong there probly isn't a compression issue.. Not sure as to why it feels different when choked as to unchoked. But keep in mind that the cams that are in it are designed to release pressure in the engine when starting the bike (even at TDC), however the same kickstarting procedure is used. Take the piston juts past TDC then give it 1 full kick. Not sure how much this helps.

  • dchooo

Posted October 28, 2013 - 08:10 AM

#3

It sounds like your bike has auto decomp cams in it. (Common conversion). On the 2001's and 2002's they came with the decomp lever, but by 04 they done away with the lever and just put auto decomp cams in them because they were tricky to start compared to other dirtbikes... This paved the way for electric start, which is why the 04's were electric start and the 02's weren't but anyways if your bike is starting fine and runs strong there probly isn't a compression issue.. Not sure as to why it feels different when choked as to unchoked. But keep in mind that the cams that are in it are designed to release pressure in the engine when starting the bike (even at TDC), however the same kickstarting procedure is used. Take the piston juts past TDC then give it 1 full kick. Not sure how much this helps.

Yes, I can feel and compare from my old cams because back there was no way that I could kick the bike over when it was at TDC. I've noticed that with the yz cams I can still feel tdc but it I'm still able to kick it over past TDC relatively much easier than with the stock non-decomp cams.

 

I'm starting to think that the counterweight on the actual cams isnt disengaging when the motor starts which might explain why I've had times when the motor just cuts out when I let it idle cold.






 
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