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YZF 250 05 Wont start after valve re-shim

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I recently did some work on a friends recently bought yzf 250 05, and checked the valves at TDC using the marks on the cam sprockets . The clearances ranging 2/1000" to 3/1000" on intake and 5/1000" exhaust. I got the old shim sizes and fitted new ones using an online calculator for the required size. Re-assembled cams correctly and tried firing it up.

It did start after a lot of kicking, and idled with the choke on but sounded horrid and was spitting flames. took the choke off and it died. After taking it all apart again, we put to TDC by checking the 'I' on the fly wheel this time and the cam lobes where facing in!

We re- positioned the cams and checked the fly wheel again and the 'I" was no where to be seen so believe this is what happened last time. SO, we did it again but held the fly wheel in place with a ratchet, after installing the tensioner everything was perfectly positioned. I checked valve clearances again and they were spot on. But, now we can't get it to start at all!

This is the limit of my experience and don't know what to do now, i know the valves could have got bent with the timing being out but wouldn't this have caused noticeable damage? Surely it would have popped the bolts out cam clamps?

Please Help

Martin

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Did you reshim it with the lobes facing in or out. The lobes should be facing out. The exhaust cam faces up and toward the front of the bike and the intake faces up and toward the rear of the bike.

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Re-shimed with the lobes facing out, thats why I was surprised when they were facing in the second attempt

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You know the crank turns twice as fast as the cams right? When you checked the I and the cams were facing in most likely it was not on the compression stroke but between exhaust and intake stroke. It sounds like your jetting is way off and your carb is plugged up. Pilot jet is probably clogged. After a good cleaning and replacing the pilot valve use fresh gas.

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Sounds like it must be timed wrong if it was running right it the first place and as you says it don't sound right now, but from what your saying you have timed it correct, I always time mine with both cams facing away from each other,

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Yes, it probably is that Swede73, after checking the first time the cam lobes were facing in at 180 degrees to where the should have been facing, so probably was done right the first time. I know its bang on now, but if it was a tooth or so out, would it be enough to cause significant damage to the valves, or the carb even, if its banging with the inlets open.

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First- Verify the cams are correct- anything but correct cam timing is just a really bad idea. Hopefully, you did not tweak the valves, but most likely, you would have felt a "clank" if you had hit the valves.

The fact it did start and run is good news.

OK, so you probably have a different issue. Backfiring, shooting flames, etc as you describe is typically a sign of lean jetting. How long has this bike been sitting? If it's been a little while, drain the carb. Gas evaporates off the light hydrocarbons or gets old pretty quickly. It doesn't take a lot of time for the fuel to become compromised in the carb bowl. Clean the pilot jet as well.

Good luck with it and hope this helps.

Edited by BazookaJoe

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While doing this the air filter was filthy, and I mean it had a crust of muck on it! Do you think that after cleaning it, its now sucking too much air, as it may have been struggling before.

Also, thanks for your help and advise everybody, it's really appreciated.

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