11 HP for Briggs/Stratton Backfires and rpm cycles - on 5500 Homelite Generator

[svlawnmower]

A home we bought has a Homelite 5500 generator as a backup. Initially it wouldn't start.

The Problem...
Now is starts every time easily with full choke and I can move it to the run position, but it runs roughly, cycling fast and slow with some backfiring. I let it run for 20 mins to 1/2 hour thinking maybe it would need to run for a bit. However it never improved. When I went to shut it off, I moved the choke to about 1/2 and it ran smoothly for about 1 minute then ran rough again. My thoughts are it may be a matter of either timing between the coil and flywheel, or adjustment on the fuel/air mixture. However, this model of Briggs / Stratton has a fixed adjustment, only allowiing about 1/2 a turn. As a result, I'm not sure where I should focus my time next.

What I have done...
I cleaned the carburetor and fuel parts, replaced gaskets and fuel hoses, fuel filter, new spark plug, flushed the fuel tank and added new. As I mentioned, it starts right up but runs roughly. I've tried adjusting the fuel mixture screw but it doesn't seem to make any impact. Due to increasing the choke causing a minute of smooth running time, I thought maybe it wasn't getting enough fuel for some reason. I'm kind of at a loss at this point and thought I would inquire for some suggestions.

I attached the Briggs / Statton Manual if helpful, and my engine information.

MODEL: 256412
TYPE: 1153-E1
CODE: 9909073A

 

[Russ2251]

Sounds like you're describing a surging issue.

Surging is caused by a lean condition as evidenced by improved
performance when choke is partially closed.
Check carb again...paying special attention to fine holes
in all orifices, emulsion tubes, jets, etc.
Even varnishing can cause an engine to run lean.
Carburetor cleaner will make the job easier to deal with.

 

[svlawnmower]

Sounds like you're describing a surging issue.

Surging is caused by a lean condition as evidenced by improved
performance when choke is partially closed.
Check carb again...paying special attention to fine holes
in all orifices, emulsion tubes, jets, etc.
Even varnishing can cause an engine to run lean.
Carburetor cleaner will make the job easier to deal with.

"SURGING"... I couldn't remember that.
Anyhow, I will try cleaning the carburetor again. I did do all you suggested but I will try again.

Thanks!

 

[Romore]

That is a 20 year old unit likely with low hours, it has probably sat a long time with gas in it. Replacing the carb may be the most economical solution, in future use a good fuel stabilizer such as Seafoam and replace the gas annually.

 

[svlawnmower]

That is a 20 year old unit likely with low hours, it has probably sat a long time with gas in it. Replacing the carb may be the most economical solution, in future use a good fuel stabilizer such as Seafoam and replace the gas annually.

I will probably try cleaning it once again now that it was running and fuel passing through. But I agree and also do use stabilizer in my small engine equipment.

Thanks!