I have an old 2500 watt 5 hp Briggs powered AC generator. It starts ok but runs rough, it seems to be running very rich. The carb is a non-float type with a diaphragm pump and only one adjustment screw, the screw only varies the roughness slightly. I took it apart, put it back together, no change. Ideas?

Yes, black smoke is too rich, blue is oil and white is steam/condensation.

Surging is normally caused by air entering the inlet manifold or governor.

All Carburetors have adjustment
Needle height
Main Jet size
Idle Jet air control (often hidden under a silver disc).

surging

https://www.google.com/search?q=18hp+Briggs+and+Stratton+surging

Carburetor adjustment

https://www.google.com/search?q=18+hp+briggs+and+stratton+carburetor+adjustment

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I would remove the float bowl bolt and run a piece of wire through the holes to make sure that there are no clogs.

If it has sat for a while, empty the carb. float chamber, flush out with clean fresh petrol. Make sure fresh petrol is in the tank and try again.

time to remove the carb and clean it...

Check the ignition wires, for rodent chewing? The ate a small place causing miss fire. I have seen this on one cylinder before, check the plugs and gaps. If all that checks ok, then make sure compression is ok. If all ok, then make sure sufficient fuel and pressure is available, and that cylinder 1 is not robbing fuel from cyl 2

Sounds like your carb needs rebuilt .This condition is caused by blockage of ports and jets in the carb .Running a fuel stabilizer will help prevent this .

With starting fluid, it runs, so this means spark and compression and valves closing properly. You mention gas flow, so gasolene is getting to the carb. This would then leave the problem being in the carb if indeed fuel is present at the carb. If you take apart the carb right now, is there fuel in the bowel? Or, remove the bottom screw on the carb, does gas flow out? Does it flow continuously or does it quit? This will indicate if the float valve is indeed opening. The only thing if you have fuel in the bowel and no start, even with the choke closed, is that the main jet must be plugged. Had the unit been sitting for quite a while with gasolene in it? Gas can "varnish" after a few months and this can cause plugging of the jets and other passages. How old is the gas in the unit? Old gas won't burn in the engine and this can also be a problem. Drain the tank, and carb, put some new gas in the unit and try it. You might have to take the carb apart again and use some carb cleaner to blow the **** out of all the carb passages. This should get it going again. Now, most important, when you get it running again, you need to adjust the engine speed so that you do not burn out any electrical equipment. If you have access to a frequency meter, plug it into the 120 volt outlet on the generator and adjust the speed so that the frequency with no load is 62 - 63 hz. This will allow the generator to drop to 60 hz under load. The adjustment is a 5/16 nut, right side of the upper engine, facing you.

When you replace the carbs on these motors it can take a bit of time for them to start and run. If there is a primer bulb pump it up and keep pumping, this is basicly force feeding the carb until it has the vacumn to get the regular supply of fuel coming in.

Your carb needs cleaned out. Tke it off and clean it out well with a good carb cleaner and you should be fine


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Low oil doesn't usually make engines cut out. Clean the air filter, change the plug and wire. If this doesn't help then I think you're looking at a carb. problem. Probably just clogged jets & ports. It's very common on small engine carbs. It shouldn't take more than 2 quarts of oil. Probably not even one.