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Yz450f only bump starts

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I have just recently picked up an 04 yz450f knowing there was trouble starting it. It won't even try to start cold unless it's bump started and will kick back when hot starting. I have the starting procedures right and have tried everything I could. Also, when I have the throttle position sensor plugged in, it will not idle for very long, then it just stops. Like somebody hit the kill switch. And it sounds like there is a slight misfire when it idles with the throttle position sensor unplugged. It does have a very strange exhaust muffler I have never seen before which worries me that the jets could be off but there's not misfire or hesitation upon acceleration. And I just recently noticed fuel pouring out of a vent on the carb. I have tried resetting the timing twice, cleaned all three jets, changed the plug, adjusted the throttle position sensor, adjusting the fuel screw and idle screw, I know the accelerator pump works, and the choke works also. I'm very stumped on this bike and could use some help. Any suggestions?

 

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Your  intake valve clearance is probably zero. That is the symptom of intake valves with no clearance.

This means the valves are mushrooming, and you need head work.

Polish the float needle and seat and inspect the needle tip (soft, no marks) and the seat (no marks) and the oring under the seat (no rotted) reagarding the fuel out of the overflow.

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7 hours ago, Krannie McKranface said:

Your  intake valve clearance is probably zero. That is the symptom of intake valves with no clearance.

A classic symptom, actually.  Contrary to intuition, valve clearance increases with heat because the aluminum head expands more then the Ti valves do, and increases the distance between the cam and the valve seats more than the valves increase in length. 

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Thank you. Was recently informed by the previous owner that the engine was rebuilt last year and hasn't ran right since. The timing was way off and I imagine the valves were not shimmed correctly. I might not have cleaned the pilot jet properly, and I am wondering if that would cause a problem of this sort

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The pilot circuit can be a major source of trouble if it gets glopped up.  For one thing, it's more complicated than you might think, and while cleaning the jet is often necessary, long term storage can cause the passageways above the jet to need work, and they can be a PITA to get at and get cleared.  Feeding a piece of very fine stainless wire or monofilament fishing line in and out of things, high pressure air blasts, and lots of carb cleaner sprayed through to verify that the passages flow well can help. 

A pilot problem will generally show up as an inability to stay running at low speeds/low throttle opening, but it depends on the severity and location of the trouble somewhat.  It could be your problem, but have a look at the clearances, anyway.  If the valves need to be reset drastically, go back in after a few hours run time and see if they are holding the corrected clearance.  If they're actually worn out, they will close up again pretty quickly.  Don't run them like that if they do, as it will wear the seats to the point that they can't be refinished without being replaced.

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Every valve is too tight. Can't even fit the smallest feeler guage we have in intake and exhaust is too tight for a .20mm. And I'm not sure what kind of shims to get or how to find out. Is there a factory spec valve shim?

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No, they are all different sizes within a range of about 175-190.

The way you find out what you need is to see what's currently installed at each valve, then subtract the amount necessary to restore correct clearance to each one.  

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