Coleman Powermate 3000 surging

The typical cause for "governor hunt" is a fouled carburetor. Could also be water in fuel.

Suggest you drain fuel, especially the carburetor fuel bowl, and put in fresh fuel. A fuel system additive such as Sea Foam will likelyl clear minor carburetor fouling.

Measure and add fuel additive per instruction... too much additive will cause high specific gravity and improper air/fuel mixture (poor running or no run).

Could also be the governor spring which automatically controls engine rpm. Under load, the governor would rev up engine to keep at optimum cutting rpm. If spring is weak, bent, or mis-adjusted, surging can happen. It is possible to adjust spring, but to do correctly, will need some way to measure rpm, and not to meby, the recommended operating rpm. Might have to replace spring if it is damaged, that is saying it is the spring. I agree with a tune up first. Plug, air filter, and fresh fuel.

Is it surging under load or not? Surging is generally fuel related and can be a multitude of reasons, most likely in the carb if it has sat. It can also be binding or sticking governor arm, make sure it is free to move, and you have the correct weight oil and level in it.

sounds like its breaking down, check your ignition system, test your leads, check your plugs, check your ignition coils etc etc etc.

govenor problem maybe does the engine sound slower when a load is on.
you will need something to read the power frequency

3000 rpm produces 50hz uk
3600 rpm produces 60hz

so if you have a meter to measure frequency you will also know what speed the engine is running at

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,.

Your RPM's are too high. There is no voltage regulator in coleman generators (generator is actually made by generac) and is 100% dependent on engine speed. There is a screw under the tank when your looking in from the recoil side. It controls the governor arm. Screw it in and it incresses the rpm, out decrease. Plug something in that draws a decent load while setting the rpms since you want it to put out 120 and 240 underload. Your idle voltage does not matter.

I've never been a big fan of the 180 OH family of engines in these things, but here goes.
1 - If the engine will stay running while it surges, close the choke a little at a time and see if it settles down. If it does, there is something amiss in the carb. The carbs on these engines are very picky about tiny bits of dirt. The good news is that they are fairly simple to take apart and clean, the bad news is that lots of the parts are plastic and break easily. At least they aren't too expensive.

2 - I've seen 2 ways to adjust the governed speed on these engines; a spring that connects to the governor arm at one end and a tab bent up from the sheet metal that mounts on top of the engine at the other - bend the tab so the spring is tighter to speed the engine up, and (b) a jam nut and screw mechanism that presses against a lever that pulls on a spring that connects to the governor arm - screw the screw in tighter to raise the engine speed.
Note that in either case the mechanism adjusts the tension in a spring that pulls against the governor arm, this is helpful in finding out where to make the adjustment.
Here in the US we want our 2 pole generators like this to run at 3750 rpm at no load so that we get very close to 3600 rpm at load. If you're using a DMM to measure the output of the generator in Hz, you want 61.5 at no load.

If nothing you can do with the choke makes the surge go away, you might have a misadjusted governor. The Tecumseh service manual has a great procedure for making this adjustment, essentially what you do is loosen the retaining nut on the governor arm, twist the governor shaft to its minimum speed position, then hold the throttle assembly at the idle stop and tighten the governor arm jam nut. Always keep a finger near the kill switch when running the engine the first time after this procedure, it's easy to mess up and have a runaway engine.

Please rank me if this was helpful,
Carl

The carburetor is probably clogged up. Mix a bottle of carburetor cleaner with the gas to see if that would help. Also check/replace the fuel filter.