Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I am working on a Honda GX390. This engine only runs if it's half choked. I can start it with full choke then move the choke to half and it will stay running. It starts missing if I open the choke all the way. It will die if you try to rev it up and then open the choke. It will rev with the choke on though. We cleaned out the fuel tank and put on a new carb with all new gaskets including the one between the insulator and the engine. We have tried running without the gas cap and it makes no difference. We also adjusted the valves and gave it an oil change. I have to be missing something somewhere. Any help would be appreciated on this one because I'm lost. Thanks ELDE

An engine that needs partial choke to run smoothly means it is running lean (too little fuel, or too much air, or both). Most often, it is restricted fuel flow due to slime/gunk in the main jet / nozzle area, and this can happen with fuel that is more than 30 days old.

Was the new carburetor a genuine Honda carb, or aftermarket?

There are a number of gaskets, insulators, etc. when fitting a Honda carburetor, including one with a tiny vent line. They can easily be installed backwards or upside down. Double check these, as well as the correct holes for the governor rod and throttle return spring.

Be sure the choke is operating properly. Here's an image from the GX390 shop manual to help:



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Robert@Honda
Caveat: I work for Honda, but the preceding was my opinion alone.