atc70 please help

[89quadzillas]

1983 honda atc 70 won't start even thou I'm getting fuel to the cylinder and the engine has 90-95 lbs compression. I suspect that it might be valve timing or ignition timing, that is keeping this engine from running, but don't know how to go about changing or adjusting either. Will someone please help with info on why this motor won't run. :beer

[Wickedfinger]

90 to 95 lbs of compression is way too low. Its only a little more than half of what it should be. You might have dropped a valve or the rings are gone. If its holding that 90lbs, its probably not a gasket issue.

[89quadzillas]

wow those little motors have that much comp.?! i thought thatd be sufficient.

[sandpuppi101]

Have you checked to see if you have juice coming out of the stator,you need fuel,compression and fire!!!

[Blown 331]

My buddy has a trail 70 that we can't get started and I check his compression and it was 35 psi. I compared that to mine which had 95 psi and it runs great. I figured it should have been around 100 psi but that was just a guess. We determined the other has a blown head gasket. I pulled the cam cover and you can see compression coming out of the top end when you kick it over. I'm not sure what your issue is but I think you have enough compression for it to run. Actually I know you do, that's what mine has and it runs great. Believe it or not I just checked it last night, kinda crazy.

[wheelie king]

She oughta turn with 90 pounds or more. I believe that comp. is sufficient.....sounds like you do not have fire, as in spark.

[42F67N]

I just took the top end off my old 70 motor it had 95 psi and wouldnt start,after i pulled the head off i could see the valves are caked with carbon.

I was told by someone on this board a atc 70 should have over 150 psi of compression and another guy told me 135.

[Wickedfinger]

Every motor is different - however, factory spec is 135 - 170psi. I don't care if it runs or not, if that 70 motor is only putting out 90psi, somethings wrong with it. If it ran yesterday, but not today and you're getting fuel - I would suspect that its an electrical issue, probably with the points rig - but - I wouldn't be happy with 90psi in the least bit. Its one thing to get a motor running, its another to get it running right. Your losing horsepower no matter how you look at it. ( I know, its just for my kid, right? ) Well, in a motor that only pumps out 3 1/2 - its a big deal. You have to be careful in those horizontal cylinder engines - because of their nature and gravity, they tend to "egg" out the bore. So if your rings are past spec and you get even a little piston slap - its a rebore or in a worse case, a reline, or in the very worst case you need to replace the rod and bearings due to excessive side to side - not just a hone and rings. Also, piston slap causes vibrations, which likes to permiate things like timing chains and that leads to cam bearings wearing and failing in 20 year old engines etc. .... I know, worst case scenario - but - just food for thought.

[Blown 331]

Every motor is different - however, factory spec is 135 - 170psi. I don't care if it runs or not, if that 70 motor is only putting out 90psi, somethings wrong with it.

That would explain why mine gets smoked by my buddy's ATC70 and he even weighs more than me. I'm rebuilding it soon anyway. It smokes a bit and the cases need split for shift forks. We are going with hi comp pistons and cams then we are licencing them.

[89quadzillas]

sorry i forgot to say- it gets good spark ( big blue anf frequent)