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Tried everything but wont start

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I bought this old POS 1990 YZ250 just to play around with but it is starting to do my head in.

I managed to get it running the day after i bought it but never since.

I have done the following in the quest to sort it.

Repaired the power valve linkage and replaced the shaft seal.

Replaced the reed valves

Replaced the spark plug (I ordered the correct one for the bike which was an 8 I took out a 5)

Checked the compression which is around 160PSI

Drained the gearbox oil and measured quantity was correct

Checked for leaks around the fly wheel

Checked the timing mark on the ignition pick up

Stripped and cleaned the carb.

Replaced the carb with another.

It seems to soak the plug after one or two kicks I wondered if the crankcase was full of fuel so i removed the plug and turned the engine over with a plummers torch held over the plug hole untill i could get no more flame from the plug hole.

I then removed the reeds and held the plumers torch in the intake and turned the engine until there was no more flames.

It still gets wet pretty quick but its better than it was but surely this isnt the carb as I have tried 2?

I have binned the old 5 plug but i had a random 7 lying around that was a little shorter and when i put this it will some times fire for about half a second before stopping and refusing to go again.

I really cant think what else to try please help :thumbsup:

Thanks

Edited by sgoaty

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Also I have checked it with a spark tester and the bike has a cracking strong spark.

I wondered if there was anyway the timing could be off even if the marks line up?

It doesnt pop or bang at all.

It has a non standard header pipe on it which looks like it is a pipe of a newer YZ modified to fit.

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It sounds as if it is getting too much fuel, you have tried it without the fuel on I would imagine. Also, you can treat it as if you had drowned it out in a stream; pull the plug and flip the bike onto its handlebars - put in 5th gear and turn the rear tire (or tyre) to clear out the crankcase. This may have happened if your had left the petcock on or it does not close completely. The other thought is that the carb is totally screwed up and just dumping gas in, bad floats perhaps?

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Im guessing they are/were not fresh carbs though... theres a reason the bikes drowning itself and theres about a 95% chance that its in the carb (even though you tried 2 deff carbs)! My first assumption would be that either the floats not set to correct height or your throttle is not closing completely. Theres a chance that your timing may be off but from my experience that would not have an effect on the bike flooding after only 2 kicks.

I know that you said you cleaned the first one but did you make sure no jet circuits were clogged?

If your certian all aspects check out, Id try to bump start it... I've had to do that with several bikes that were being a PITA to start, and have had no issues with any of those bikes since they started that first time.

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Ill check the float height in the morning and see how it looks. It could be both carbs I suppose as they are 20 years old

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