Very odd starting problem on wr450

I have a 06 wr450 that I rebuilt the top end of last winter. Got it back together and it ran great but was a little bit harder starting and the electric start no longer would start it. It turns it over and seems to do everything except start it even backfiring a lil bit. But the kick starter started it just fine. I rode it all year(about 13 1 1/2 hour harescrambles). But, At the last race of the year it wouldn't start at all. I got it started by rolling down a hill and it ran perfectly, even shutting it off and starting it up right away. But if I let it cool down it wouldn't start again. So just to bring it all together, the only way my bike will start is If I kickstart it about every five minutes once it is already warmed up. Where do I start trying to diagnose the problem? I think it's a carb problem but why does it run perfect once it's started but only have problems when I let it cool down for more than five minutes? Also any ideas on why the e start doesnt work? Advise would be greatly appreciated, thanks

Edited by Wr822

Have you checked your valve clearances? It sure sounds like the clearances are off, and possibly your cam timing is off too! That is where I would start looking. Maniac

Even if it runs perfect once it's started?

The no estart is a tell that the cam timing could be off, in fact that's a common complaint when you advance the exhaust cam to a YZ position. The valve cover is easy enough to pop off, that's where I'd start.

My 06 and my buddys 09 won't e start cold if the battery is weak and will backfire out the exhaust during cranking. Cranks ok but was told there isn't enough voltage left during cranking with a weak battery to run the ignition properly as the starter is using it all up. It's best to kick start when cold imo. Tight valves can also cause a hard start problem. I check mine every year and have been great so far.

So nobody thinks it is a carb problem? Yeah I replaced the battery when I first got it back together and it wouldn't start with the estart but it didn't fix it. I really don't even mind not having it now except for when I'm stuck on a hillclimb an hour into a race when I'm gettin tired and that takes away the rest of my energy for the rest of the race! The biggest problem now is that it won't start at all now even with kicking it, unless already warmed up, the valves were good 25hrs ago but I was planning on checking them this winter. The timing was also right but I'll check it again. Remember it kick started fine until all of a sudden one day it wouldn't!

Edited by Wr822

No other theories??

It could be in the carb but without having it in front of me it's tough to tell. Possible: vacuum/air leak, starter jet plugged, ignition failure, bad valve, timing chain skipped. auto decompresion working or sticking?

1) If it started acting up after a top end than got harder to start later I would pull the valve cover and have a look at cam timing and valve clearance.

I use stock cam timing only. I think advancing the exhaust cam (or whatever that yz timing mod is) is 400cc & 426cc only. Like the other guys said tight valves can run ok but be way hard to start.

2) check the plug and make sure you have good spark and good fuel

3) is compression ok. I think you would notice somthing is up when kicking it.

or open the carb up and make sure its all clear.

you want to check the valves anyway so start there and eliminate that. look everything over good and rotate it around to be 100% sure its happy under the valve cover.

thats what i would do :smirk:

Sure we can come up with theories, is that what you want? Or do you want us to tell you where we would start looking if it was our bike? Have you looked at anything these people told you to look at? Again, that's where we would start if it was our bike. Maniac

Thanks a lot guys, I haven't had time to start tearin it apart yet but now I know were to start when I get into it probly next weekend, thanks again, chris

Let us know what you find. We do want to help. Maniac

Ok, so a quick update, my Exhaust cam was out of time 1 tooth up( is that retarded?) ! So i guess I need to ask now, how it happened right? If I didn't set it like that, is the only way it could have skipped is if the tensioner is bad? The tensioner felt fine per the manuals testing procedure. But knowing that it never started with the estart it makes sense that I set it like that when I put it back together last year right? One other question, I also unfortunately found my boot from the air box to the carb to be not tight, so I figured I better take the carb off and clean it. What all do you do to clean this type of carb? I've only had a little experiance with a law mower carb so I don't really know what I'm doing and don't want to do something stupid and mess it up. Thanks, Chris

Edited by Wr822

More than likely, your cam timing was off by one tooth when you put it back together last year. It is possible that your tensioner is bad, and/or your cam chain. Did you install a new cam chain last year? They are fairly cheap, and a new one is good insurance. But having said that, I still think it was human error from last year. It's pretty easy to get the cams one tooth out of alignment when re-installing them. Do you have a manual to help you in cleaning the carb? More than likely, you can just remove it and spray some cleaner thru the carb bore and any orifices that you see in there. This should clean it well enough. I would tell you to clean it completely inside & out, but I think that might be beyond your current capability. Any buddies that might be able to help? Maniac

Thanks bud

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