Briggs 12 hp engine troubleshooting

Hi All,

I bought an older MTD riding mower with a briggs 12 hp engine. It ran, but needed a tune up. One minute it would act like it was surging, then act like it was missing out.
So I started with the basics. New air cleaner, plug, gas, gas line and filter. Took the carb off and soaked it for 30 minutes in carb cleaner. Blew out all the parts and passages with air nozzle. Float and needle are in good condition.

So reassembled carb. Set both scews out 1 1/2 turns from seated. It stared right up and ran smooth at idle. Half throttle it started popping just a little. Full throttle and still more popping from the muffler. Tried tuning it in with the high speed screw on the bottom of the carb. No matter which way I turned it, not much difference until it would start to bog down. Still one minute it acts like it is surging and the next acts like it is missing out. Popping from the muffler is the most noticeable. When I bring it back down to idle after running at full throttle, it surges bad.

Can it be the valves? How are they adjusted on this engine? Any advice is appreciated.

Model 281707, 0411 01, 90011631

Thanks,
Cory

 

Try spraying/dribble some carb/brake parts cleaner behind the carb at the mating surfaces of the carb and blocl, if the engine tempo changes you have an air leak probably a failing gasket and it is sucking air rather than fuel. Have a good one. Geo

 

Tried the carb cleaner all around the carb and gasket area. No changes in rpm's. Did fine tune the high speed screw some more. Got it to run smooth at full throttle for a couple of minutes. Thought I had it, then started the popping out of the muffler and surging. AAAAHHHH. I am going to beat this carb if it kills me.

 

Still something in that carb. Get a tiny wire like that out of a twist tie on a bread bag and push it through all the jets and holes in the carb. Don't forget the ones on the inside of the throat right where the throttle butterfly closes. There should be several there. Take the jets out, blow it all out, and try again. Sometimes you have to clean a carb many times before you achieve success.