So my buddy and I was going fourwheeler ridding I started up the trailblazer started on first turn everything was good drove it on the trailer got to the park and it would not start and I have not been able to start it sense I have rebuilt the top end stock piston size put a complete new ignition system from stator, recitifier, cdi, coil, plug all that and still nothing, now I was an idiot and scratched the piston up a bit only one scratch but goes half way down piston. but it is getting good compression the crank seals are good cuz it is pulling gas in and I checked for leaks or play no play or any leaks but the only way itll back fire or spark is if I hold my hand on the carburetor and get it to suck pressure and itll back fire so im at a loss did I miss a step rebuilding top end which was only 90 psi which is why I thought it wouldn't start but yeah idk now. Help please

 

First off installing a stock piston and rings in a worn cylinder almost never works. 90 psi is too low to even run right if you can even get it cranked.. Have the cylinder measured for an over size piston. If cylinder isn't worn too bad, a first over .020 Wiseco piston kit is the best you can install in the 250. Plus you can't tell whether crank seals are good by just looking at them. They're cheap and best to replace at least the main one that fails,the one behind the drive clutch when you do the top end.

 

ahhhh ok cool I didnt think that the cylinder looked to bad live and learn thats what I love about this. I know ebay has a shop that will do it for 150 so ill look into that. ill change the one behind the clutch but if the other crank seals are bad is there any way to remove the engine without pulling transmission off cuz I know ill have to split the case to change those other two seals and I might go ahead and do it as well as crank rod if the engine can be removed without removing the transmission.

 

You have to pull the flywheel and stator to replace the other seal. Engine doesn't have to be removed,but is harder to get to. The main culprit is the seal behind the drive clutch and easier to get to. The transmission is separate from the engine if you decide you want to pull the complete engine and rebuild it..