Old LT80 won't turn over
 

I'm new to ATV's. I just got an old '87 (I think) LT80 for free from a guy who never got around to working on it. I started off cleaning it out, had a mice nest in the inttake and alot of debris even down to the intake on the carb. Broke the carb down and cleaned it out with carb cleaner spray, pipe cleaners, and my wifes toothbrush:D. Broke down the oil pump and did the same. Brand new battery, spark plug, oil, gas, air filter. Let any old fuel and oil drain out of the engine, cleaned the piston head of carbon and checked the cyl wall for scratches (none, shiny) rotated the crank by hand and got a nice thunk from the piston so I know I'm at least getting some compression. reassembled and tried to start.
e-brake is up, fuel toggle to pri, even tried on run and res, choke up

It tries to turn over, if i give it just a little gas it'll try harder. It actually fired up for a minute and let out a nice smoke cloud, once it cleared up I let off the gas and it died, haven't got it started since. Every now and then it'll backfire a bit when cranking and speed up like it's about to start. Don't know where to go from here. I tried to put as much info as I could here please ask if you need anything else. I would like to get it running by this weekend if possible, thanks.

Welcome to the forums. :)
I'd check the compression and see if the pipe is plugged.

So I broke the carb don again and got some grit out of the smaller jet, I guess I missed taking this jet out last time. Still no start. Took off the exhaust and made sure it wasn't clogged, made sure I was getting sparc at the plug, it sparcs fine, spraying starter into the carb intake or into the piston and starting doesn't help. Though I'm getting closer. Now instead of hearing the starter spinning the whole time if I give it about half throttle with the choke on and tank on PRI it'll sound almost as if it's running like a pupupupupupup sound but not like it's running on it's own and when I let off the start button it dies instantly, if I give it more or less throttle it stops the pupup sound and goes back to the starter sound (sorry I'm tryin to be discriptive). I don't have a compression gauge, but I might be able to pick one up this weekend if ya'll think that'll help.

We have to know the compression at this point.
Right now I'd say it's a 95% chance that it's a compression problem.
I got mine at Sears.

Alright I went to a public auto shop here on post and got to use a compression tester for $4 (great deal considering it could have been a $30 purchase). It cranked it 4 times and got a consistant 53psi (somewhere between 50-55psi the dial on the gauge was in incriments of 5). It was suggested there that I get a book on it and ohm out my ignition system and make sure that my what spark I do have is actually good enough. Also my mixture might not be right bacause it only attempts to start like that when the choke is on and I give it a little throttle. Any suggestions?

Okay so a little more digging in these forums, mosty looking at LT80's posts and I'm guesing my compression should be around 120psi? Remember this is (I believe) the '87 LT80 model. So with 50-55psi on mine where do I go from here? I need help on where to start with a 'top-end rebuild' what does that include and is there instructions online?

Oh I forgot about this when I was cleaning it out, don't know if this explains it. I took off the 'head' to look at the piston, removed the head gasket and cleaned off the top of the piston, lots of carbon build up, the walls diddn't have any visible damage to them. When I was putting the gasket back on I accidentaly bent it, I bent it back in place and put it on, bolted the head back on. Could me bending the head gasket be my problem?

I'm guessing a worn out intake valve? check your valve lash

Isn't that quad a 2 stroke?

Yes it's an 82cc 2-stroke oil injected engine.

I don't know anything about 'valve lash' so please explain.

sorry, my bad, I did not know that it was 2 stroke.