Will tight valves cause these syptoms:

2009 YZ450F, about 50 hours on it. After getting the engine to a nice warm temp (20 min of riding or so) my bike starts to run like it's lean (pops and has more engine braking) and stallsl a lot. I does this with predictable repetition, and it seems to be related to engine temp. I've tried different jetting, which seems to make a difference in the way it runs for the first 20 min, but it does not improve the running weird and stalling issue after 20 min. I just checked the valves, and they are all on the tight side. All of the intake valves will barely fit a .10mm and all the exhaust will barely fit a .20mm. They fit, but with a bit of pushing, definitely more than what I would call a light drag. I think each of them would nearly come in to the middle of the range with a .05mm, but maybe I'll get some Honda shims so I can get them in .025mm increments.

So are these symptoms of tight valves?

Seems alittle early for valves to be tight. But when mine were tight it was hard to start after riding it for a little while and it just didn't feel right. If the valves are tight I would adjust them.

I'm going to adjust them, I've got a shim kit on the way. I really hope this takes care of the problem, it's driving me nuts!!:busted: /it's been going on since I bought the bike earlier this year.

Update: I rechecked this morning (I let the motor cool for 3 hours after riding before I checked them last night-that wasn't enough time apparently), and I found only the middle intake valve tight. All of the rest are comfortably at the min spec.

So...would a tight intake valve cause these issues?

Why don't you just adjust it and see if it fixes your problems. When my right and middle intake was tight the bike ran like crap and didn't idle very smooth.

Why don't you just adjust it and see if it fixes your problems. When my right and middle intake was tight the bike ran like crap and didn't idle very smooth.

That's the plan, I was just hoping someone that has experienced the problem before could chime in while I'm waiting on a shim kit.

make sure your cold start knob is in the in position (off). might be your problem after warming up.

make sure your cold start knob is in the in position (off). might be your problem after warming up.

It is, and I checked the hot start system to make sure it wasn't hanging open as well. I'm somewhat confident that the tight intake valve is the root of the problem. It's so closely related to engine temp that it makes sense that the valve clearance would get too small and cause the valve to hang open when the engine is warm. As a matter of fact I can recall thinking that the compression seemed weak while kicking it after it stalled several times on the last ride.

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