Every spring a few of these have developed enough deposits on the valve stem to allow the valve to stick open. They tend to occur in lower hour machines that have old fuel left in. Sounds like you're in good hands either way.

Ditto on that diag. Seems all too common with new gasoline formulations and tighter clearances on intake valves to reduce emissions.

From now on use Sta-Bil fuel stabilizer/fuel system cleaner in your gas can every time you fill it. In addition, 1 0z/gal of Marvel Mystery Oil would be great.

Story time: I did this to myself back in the '70s on an old B&S 3.5 HP mower. For some reason I decided to add some old alcohol to the mower's fuel tank. The mower ran fine. The next time I went to use it, no compression. Suddenly it hit me - I had used the alcohol to clean a brush that I had done some varnishing with! Okay, I put the brain in gear and came up with the plan - put in new alcohol. I drained the tank and replaced the fuel, adding some pure alcohol. It took several days of pulling the starter cord every few hours, but the alcohol eventually dissolved the varnish on the valve stems and everything was cool. Interestingly, I bought that mower in the spring of 1971. The deck eventually cracked, so I swapped the engine onto another deck. Around 1984 I bought a nice mower from the old man next door and sold my old one to a fellow worker. He used it for a few years, and offered it back to me because it wasn't running right. I took it home again and fixed it - the intake manifold had come loose. I kept the thing around, still running fine, until 1994, when I moved to a new house. I gave the mower to my wife's cousin who has a mobile home out in the country. As far as I know, the thing is still running.

Thanks for the responses. I understand what the responses were about. The funny thing is that I have two mowers that are identical. I bought them off ebay and have used them for almost three years. I have treated both of them the same way. Every year I use sea foam in them to treat the mower and the gas. I have never had a problem like this with either one. I have tried to take care of the mowers because every other time they have taken care of me. I hope that it is something that can be fixed and not to costly.

Thanks again for the repsonses.

Mark

Well, maybe we're out in left field with the stuck valves theory. Perhaps the compression release stuck or something has gone very wrong in the overhead cam system. On the other hand, 'treating with seafoam every year' is not the same as using it or a dedicated stabilizer in your fuel all the time, and what might happen to one mower has no bearing on what may or may not happen to the other mower.

Saxman1, I wasn't trying to make it sound like the problem couldn't happen to just one mower. I do put the seafoam in the mower every month or so. I usually treat the "new" gas as soon as I get it from the station. I am still hoping that it is something small to fix.

Mark

I would go with Timothy Garon. Remove the valve cover. The plastic cam compression release may be frozen and keeping the valve open.