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2000 yz80 help!

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I have a 2000 yz80 I bought a new top end kit and still won't start, it has spark, I cleaned the carberator and still won't do nothing what can it be please need some good advice....

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These yz80 and 85's are very simple, no powervalve motors. I'd start with the basics, it may spark but does it seem strong enough. I recently ran into a weak spark issue myself. Does it fire at all? How does the kick lever feel? Decent compression.

Next how was the cylinder? Was it worn beyond the spec? Hows your piston to cylinder clearance? also Are you positive the piston is facing the right way with the Arrow facing the exhaust.

How are the reeds? They should be fully seated with no air gap. Could also be numerous other things that you need to go through one by one.

How did the bike run before? Did it blow up or just a scheduled top end.

Whats your compression psi? should be at least 125 psi min for a yz80

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I have a 2000 yz80 I bought a new top end kit and still won't start, it has spark, I cleaned the carberator and still won't do nothing what can it be please need some good advice....

I read your exact situation MANY times. 99% of the time the core problem is lack of compression. Just because you installed a new piston does not mean the engine has adequate compression. Most all novice mechanics have no means to check the tolerence of the cylinder, and simply assume "it looks ok, so it must be good" . Like others commented you need to start with a basic and systematic approach to find out what's going on. First, I highly recommend you buy/borrow a compression tester, and test your compression. This is a simple and quick test that will tell you immediately if you have a healthy top end or not.

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It doesn't fire at all no puff nothing  and yes it ran before till I cracked the piston and now bought a new bottom end with the same top end & New piston and rings ,  and yes I faced the arrow towards the muffler area, the kick lever is decent when I kick it , it has spark and also the other day I turned the gas line on and the carberator was leaking from the bottom hose like.  Streamin, ???  I haven't checked the compression yet where can I buy a tester at? 

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You can buy a compression tester at sears, harbor freight, or most auto stores. you can even rent one from pep boys or auto zone.

It sounds like your running a old cylinder that had a cracked piston. More then likely that cylinder needs replated after a accident like that.

For the fuel running out of the carb if its coming out of the overflow then it needs a float valve needle. Or you have a problem with assembly, possibly the float pin came out. pull the carb and float bowl to inspect. Did you replace that when you did the carb "rebuild"?

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I bought a new piston for it basically a top end  kit,  it didn't had spark so I bought a bottom end and now it does, I put everything together and the bike wouldn't start maybe this could be a carb problem, and I'm gonna see if I can rent a compression tester from a friend of mines, every time I take the top end apart and pull the jug off there's like a little puddle of gas Sittin near the rod , can it be gettin flooded with gas, I don't wanna give up on this project....I love this bike...

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I bought a new piston for it basically a top end  kit,  it didn't had spark so I bought a bottom end and now it does, I put everything together and the bike wouldn't start maybe this could be a carb problem, and I'm gonna see if I can rent a compression tester from a friend of mines, every time I take the top end apart and pull the jug off there's like a little puddle of gas Sittin near the rod , can it be gettin flooded with gas, I don't wanna give up on this project....I love this bike...

Explain that sentence better...Did you remove the flywheel? If so did you make sure the wodruf key is in place and that timing is right?

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No I never messed with the flywheel I bought the whole bottom end used and just put the new piston and rings on and still won't start, and by flywheel are you talking bout where the gear shifter is at behind the cover?

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How can I do that and what are my major problem here just so I can know because the bike used to run mint before

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Why did you switch to this new- used bottom end? What was wrong with yours?

You said you had no spark with your old bottom end but The only parts that effect spark are the stator and flywheel. Nothin in the bottom end.

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