Why does my 250cc quadrunner have no compression with a new top end?

Valve lash and/or valve timing.

Hey Marty,
An internal combustion engine requires three things to run..(if all the internals are good)..
1. A properly timed spark.
2. Adequate compression (>120psi).
3. Proper air/fuel mixture.

Start by eliminating one of these at a time...(get a professional to clean and set the carb), install a new spark plug. Get a new fuel line.

If you ran it with straight Gan you could have trashed the rings lowering the compression enough that it will not start. Do a compression check and see what it has. Make sure you have a 32:1 or 40:1 mix if you are not using the injection system or if it is not working. Quality oil too. Don't do the compression check without normal premix in there. You need at least 110 lbs to run on the low side although I have seen some run at 105.

You seem to have many problems with this ATV reading the different postings have you checked the compression on all 4 cylinders if so what were the readings ?

If its a 2 stoke,"takes gas oil mix", piston in backwards,, ,,,,if its a 4 stroke "takes gas only"...rocker arms need adjusted, or cam not set in proper place during resembly "out of time". Or a. Bent valve/valves,,,in the head, valve will have to be replaced

i would adj valves 1st and go from there. rings maybe stuck if it has sat a while w/o being started. run a compression test on it should have something at least. no compression doesnt sound right to me. if so rings stuck can be freed if so ,sometimes fixes it ,sometimes breaks it

bad rings, bent valve, bad valve seat. make sure your oil pump is good once you figure out too.

First question since i am assuming it was just sitting around for some time if i am correct you need to pull the carb remove the float bowl and components if everything was done correctly with your rebuild the likely problem is your carb is gummed up remove everything in the carb low speed jet etc. soak everything in sea foam fuel cleaner overnight and hopefully you have some compressed air and blow out that low speed jet and passage way pay close attention that you have see fluid coming from the other end and check the jet make sure it is unclogged hold it up to the light.

I have a 87 quadrunner 300 how do I adjust the valves it has 4 2 on intake and 2on exhaust

it needs a set of rings and maybe a piston then it will be like new again