Onan 5500 Backfires and Dies under a load

Chum lee wrote:

lakecityemt wrote:

Chum lee wrote:
"I assume from the backfiring?"

I can't see it or hear it run online. That said:

Backfiring implies that unburned mixture IN THE INTAKE tract is being ignited and burned. (not the exhaust) Can you confirm that? Backfiring is a classic condition of a lean mixture which would point to a vacuum leak somewhere in the intake. Are all the breather hoses connected properly? Is the (new) carburetor properly seated on the manifold with all the gaskets? When hot, a lean mixture can lead to pre-ignition/detonation which may sound like a backfire.

What happens if you manually force the choke on with the engine warmed up, loaded, and backfiring? (richen the mixture) Any improvement?

Do you have a compression tester? If so, does the engine meet the compression specs?

Chum lee

Chum you might be a bit over my head, LOL... I will ask him to try and manually adjust the choke when its backfiring. No compression tester.

OK let's try something simple. Your carburetor should have an altitude compensating adjustment screw. It has some control of your fuel mixture adjustment which should be set for your current altitude. It that set correctly? Having it set too high for your current altitude can create the symptoms you have. For example: If you are currently at 1500 feet altitude, adjust (turn) the screw so that the pointer is between 1,000 and 2,000 feet. Look at the screw adjustment on the carburetor, it will be obvious.

Chum lee