Craftsman Briggs 14.5 HP Engine Surging at Full Thottle

[polarred21]

Seems to be an age old problem but haven't fixed mine yet. Here is the story:

1. FIL's late 90's mower sitting for 3 years want to get it running to sell.

2. New gas then float stuck, hydrolocked, filled crankcase with gas, lots of smoke, and a heck of a mess. Spark plug looks good, have removed and cleaned several times during this process. This carb also has the electric fuel solenoid on the bottom.

3. Oil changed twice and then cranked and run fair. Eventually ran good except full throttle engine will surge. THIS IS NOT MINE but the exact same symptoms:
https://www.youtube.com/watch?v=7NpSlCZgrKg

4. Pulled off the carb and what A MESS! I thought this was the problem, removed and cleaned really well with carb cleaner spray can and blew all ports out.

5. Reinstalled clean carb and same symptoms, no change.

6. Thought about a new fuel filter and decided to pull line off carb to check gas flow and it is flowing wide open here, so ruled this out.

7. Engine starts perfect everytime and idles well. About 90% and above throttle it begins this surge.

8. Pushing the throttle further into the choke position the surging stops as if starving for fuel with no black smoke.

9. Have adjusted the air/fuel mixture many times even removing the plastic cap for more adjustment but no help.

What's next? The carb looked good after I cleaned it but is it most likely still the problem?
Thanks

 

[jerry56]

Dump a little sea foam in it and run it for a while, if it smooth's out with a little choke then there is probably still a little dirt or debris in the carb....if it isn't huge the sea foam will clear it out....I use it all the time....

 

[polarred21]

Thanks for the advice, wish I would have tried that. Instead I pulled if off again for a more thorough cleaning and screwed up the threads on the main jet when I took it out and now can't get it back in the carb due to the internal threads being scored.

Unfortunately, now have a new $$$$ on order.