10 hp Briggs & Stratton oscillates under load.

[UnclKracker]

The engine is part of a 5000 Watt Generac generator. I bought the generator used from The Home Depot. Someone returned it when it wouldn't start. It had a bad Armature. I used it for about 12 hours before it failed to start again. Another bad armature. Since the armature has been replaced again I have only started it occasionally and run it for 20 minutes. I always run the carburetor dry and burn only non-ethanol gas. Today it was very difficult to start. After warming up it was running smoothly, but after several minutes it would oscillate for several seconds and then smooth out again. If I add any load to the generator it oscillates continuously. Could this be another armature? If so, why is this happening?
I had an audio file of the engine, but I don't know how to attach it. I guess this forum doesn't support them.

 

[ILENGINE]

By oscilating I am assuming hunting and surging. I would think more of a fuel delivery issue. Basically not getting enough gas under load to keep constant engine speed, But could also be related to a too sensitive issue with the governor can also cause surging under load.

 

[UnclKracker]

Thanks, Ive always kept the carburetors bowl empty between uses and burn. nothing but ethanol-free gas, but you could be right. I will check prices of a new carburetor. probably cheaper than taking it to a shop. Even if that isn't the problem.

 

[UnclKracker]

By oscilating I am assuming hunting and surging. I would think more of a fuel delivery issue. Basically not getting enough gas under load to keep constant engine speed, But could also be related to a too sensitive issue with the governor can also cause surging under load.

Yes, by oscillating I mean its like having a foot throttle and pumping it several times second.

 

[Ocean909]

Check to make sure the spark plug is tight. I've had a generator or two run like crap because of a loose plug.

 

[UnclKracker]

Check to make sure the spark plug is tight. I've had a generator or two run like crap because of a loose plug.

Installed a new sparkplug & new carburetor, fresh non-ethanol fuel.
Started better and ran ok until I added load to the generator. Then it starts searching (oscillating) the same as before. It occurred to me, I had replaced the magneto armature a couple of years ago. Since then I haven't had a need for the generator. I've started it several times with the new armature but hadn't plugged anything into it. What if that armature was defective and wasn't producing a strong spark? I've rechecked the armature clearance. It's supposed to be between 0.006" and 0.010". I set it again to 0.008"
It seemed to improve a little but still not enough.
I would think the armature would be either good or not functioning at all.
Has anyone ever known an armature to be "weak" but still produce a spark?

 

[Tiger Small Engine]

Installed a new sparkplug & new carburetor, fresh non-ethanol fuel.
Started better and ran ok until I added load to the generator. Then it starts searching (oscillating) the same as before. It occurred to me, I had replaced the magneto armature a couple of years ago. Since then I haven't had a need for the generator. I've started it several times with the new armature but hadn't plugged anything into it. What if that armature was defective and wasn't producing a strong spark? I've rechecked the armature clearance. It's supposed to be between 0.006" and 0.010". I set it again to 0.008"
It seemed to improve a little but still not enough.
I would think the armature would be either good or not functioning at all.
Has anyone ever known an armature to be "weak" but still produce a spark?

Hopefully you didn’t throw old carburetor away. Clean OEM carburetor or take it to shop. Has an air leak or dirty jets/carb. It is probably an air/fuel mixture issue. Don’t keep throwing parts at it, start with original CLEAN carburetor, and good gaskets and go from there.

 

[UnclKracker]

Hopefully you didn’t throw old carburetor away. Clean OEM carburetor or take it to shop. Has an air leak or dirty jets/carb. It is probably an air/fuel mixture issue. Don’t keep throwing parts at it, start with original CLEAN carburetor, and good gaskets and go from there.

I still have the carb. I'll try anything, but the fact that it performed perfectly before the armature failure leads me to suspect it as the problem. I will try try cleaning the carb, and offer you an attaboy if it is the cure.
Thanks for your thoughts.

 

[UnclKracker]

Hopefully you didn’t throw old carburetor away. Clean OEM carburetor or take it to shop. Has an air leak or dirty jets/carb. It is probably an air/fuel mixture issue. Don’t keep throwing parts at it, start with original CLEAN carburetor, and good gaskets and go from there.

 

[UnclKracker]

I replaced the armature. The engine runs fine now.