This little forklift has a problem keeping its rpms up during a load. It will start and idle just fine, but when it climbs up the apron, it bogs down like it is flooded. I can put it in neutral and rev it up to get it to smooth out, and then try again. I've adjusted the carb in the normal way, but it does little good.

I'm suspecting the fuel delivery system, starting with the IMPCO converter. When I push on the little primer button while engine is running, there is no difference in engine speed.

On this converter, the atmospheric vent balance port has a tubing fitting, but no tubing to anything. If I put my finger over the vent balance opening, the motor dies.

Thanks for any insight.