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- Jake -

Took my cylinder head off. How does it look?

10 posts in this topic

So I've got this problem where my 03 WR450F won't rev past about 5000rpm.

I've checked everything I can external of the engine and still not found the problem, so today I've stripped the cylinder head down to see if there anything wrong with the piston or the valves.

Although I've stripped loads of two strokes in the past, I've never messed with valves before. The head and valves look fairly OK to me, as far as I can tell, although there's a fair amount of carbon build up.

Anyone see anything obviously wrong here?....

img1821l.th.jpg

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Should I continue and take the valves out? Should I take it to a shop as it is and get the valve seats recut?

Thanks for any advice.

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Did you try a new coil and /or stator? It will not be the valves or piston. But since you have the head off you can pour some solvenbt in the head and check for leaks. If you have some leakage, then do the valves. Or do them to be proactive. Unless you own a Serdi valve seat cutter, take it to a shop that does.

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No, I haven't tried replacing those. I'm not real happy replacing parts unless I know they are faulty. Spending hundreds to replace parts that are working fine doesn't seem like the way to go.

So you're saying my problem couldn't a sticking valve or somesuch?

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Not a valve.

If an engine starts to run poor at high speed, you know you have fresh fuel and a carb in good condition (needle jet emulsion tube not worn), clean air filter, new spark plug, the failure is often the stator and sometimes the coil.

I'd borrow a coil and test ride, if the problem exists still, I'd do the stator. I assume you've checked all connections and they are good. If everything was working fine, your bike would be running good. Something is amiss.

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Thanks, GuyGraham.

I've checked that part and it looks completely clear and clean. I don't know how I would tell if it's worn, which William suggests. It appears to be like new.

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Very hard to tell it is is worn with the naked eye.

All it needs to be is a few thous worn and it will give you grief. I keep one on hand. Being it is so easy to swap, I pop it in to confirm if it is/is not a problem.

I doubt your problem is the coil.

I would of first tried a new emulsion tube (cheap part), then a stator, then a coil. But I'd first go over every single wire and switch carefully.

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Sadly, the meter tests only tells you if it is completely shot. What happens with stators and the crank position sensor is they begin to fail at high RPM and/or only when hot and over time get worse and worse. It is rare that either it works perfect or fails enough to be out of spec.

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