Ask The Editors: Spontaneous Compression Loss
Sounds like it’s time.
Today I decided to get it running and it will not start but turns over easily. I put a compression tester on it and I only get about 70 psi. I do not think that is enough but its been running great for the last few months? Do ATVs just lose compression while they are running?
Given that your machine should be reading somewhere between 100 and 120 PSI, we’d certainly say you’ve isolated your problem if you have only 70 pounds of compression.
While it’s rare for a machine to literally lose compression during operation, looking at what causes compression loss in the first place certainly leaves the door open for it happening at anytime. With a 2-stroke like your 350, top end replacement is simply a way of life. Rings in particular wear with frequent use and once material loss is such they don’t mate up perfectly against the cylinder wall, cylinder pressure (compression) is free to leak into the bottom end.
Additionally, pistons themselves wear over time – with the same consequence.
It sounds to us like your machine is due for a new top end. When you do it, it’s wise to go ahead and replace the piston and the rings and of course the gasket. This should get you back in action.
