Generator surges even under load - Coleman Powermate Portable Generator PM0435003

Yep - the carb needs to be removed and cleaned out thoroughly to remove the clogging responsible for the surging. Motor needs a smooth supply of gas - look at what your car does when you jerk around with the gas pedal. Also check the governor area of generator since that keeps motor running at a certain fixed speed. If there is something wrong with it, that will also cause the problemo.

does it surge under load ? or without load, if without load it could need the injector cleaning if under load it could be the governor at fault

Check for a weak or missing spring on the throttle linkeage.

That sounds like dirty/clogged idle circuit passages in the carbureator. A little spary carb cleaner might work, but you might have to rebuild it.

Most likely, the carburetor needs cleaning.
There are two main jets powering your Yamaha, the pilot, or sometimes called the idle jet, and the main jet. If the pilot jet is clogged, the main jet will take on the load, and the governor will modulate the carburetor to keep it running, causing the surging problem. Likely, the problem is less, or even nonexistent if the choke is on, or the generator is under load.
Search the web for help on cleaning this pilot/idle jet.

It definately sounds like a fuel problem, lack of fuel..I assume it is running on LP or natural gas. The hose running from the demand regulator goes to the carburetor/mixer. When it gets to the carburetor, there is an adjustable main jet. It is different on different models, but is usually easy to find. There is probably a screw slot in the end of the screw head and a spring under the head. Start it up after locating the screw and open the jet just enough to even out the running. It was factory set, but barometric pressure and altitude and different fuels in different areas will decessitate different settings.
Please let me know if this fixes your problem, Robert

i have the same problem with a new one ,take a peace of paper and cover the battery cover air inlet when it's running ,if your problem stops-it's the seal around the cover,a honda rep let the cat out of the bag,---jk

A generator should normally surge under load.It is designed to do as a means of saving fuel while being able This increase energy supply when necessary.

I had a Colman that only surged when it had a large load on it. ConsumerReports.org says that some Coleman generators just can't hold a constant voltage. Hondas are expensive but very good,.