16 HP B&S Vanguard dies suddenly after 30 minutes or so
I have a circa 1995 Briggs and Stratton 16-HP V-Twin Vanguard engine that runs very well for 25-40 minutes, then dies suddenly. The runtime before it dies seems shorter in hot weather. It will restart briefly, then die again in a few seconds. Allowed to cool, I can repeat this cycle. There is no warning before the engine dies. There is no loss of power, no surging, no stumbling. Nothing. It is almost as though the ignition was turned off. I have done the following:
- Adjusted the valves
- Replaced the fuel filter and fuel pump (the filter seemed to empty during these episodes, but no longer)
- Tested the fuel solenoid on the bench. I also heated it up with a propane torch. It seems to be working OK. This solenoid has no protruding plastic pin. It is part number 807744.
- Checked the fuel cap for a clogged vent, but I can see no vent in this cap at all. It has a mechanism to display the fuel level.
Right now, I'm thinking that the fuel solenoid may still be at fault, but due to electrical issues rather than mechanical. Maybe a short somewhere? But that wouldn't explain why it dies when good and hot. I have seen discussions which recommend replacing that solenoid with a simple 3/4" bolt to test the solenoid, but I can't see how fuel would get to the main jet, since a bolt of that length would be threaded past all of the holes in the threaded main jet shaft. I found that part 691511 should do the trick, but it'll take days to get one. Just buying a replacement solenoid would be an expensive risk, as it's $90.
Another possibility would seem to be one of the magnetos, but the engine dies so suddenly and runs so well before, that seems kind of far fetched to me. I would expect that only one of the two would be bad and that the engine would run poorly for at least a short time with only one. I could just replace both, but I'm looking at about $75 in parts to do that.
I have not cleaned or rebuilt the carburetor. It looks surprisingly clean but the float bowl gasket is rather dry. I sprayed it lightly and in the jets with carburetor cleaner, but I haven't done much else. I would think if it was a carburetor clog of some sort, it would show up much sooner after starting.
Any ideas anyone?