"4 Cycle Engine Surging or Hunting"

By Ron Stultz

2 June 2007

Update: 28 August 2024

When a 4 cycle engine rev's up and then drops back and then rev's up and drops back again, over and over, usually at a slow throttle setting, this is called surging or hunting.

Surging or hunting is caused by an obstruction in one of the small passages in the carburetor (carb) and the recommended approach to fix this problem is to remove the carb, take it apart and soak the carb body in solvent over night and then use compressed air to blow out all passages. I have done this, and it does work but before you go to the trouble of removing and soaking, try mixing a complete bottle of STP Carb and Fuel Injection Cleaner with one gallon of gasoline and running the gallon through your 4 cycle engine. Yes, a complete bottle seems like a lot in one gallon but it has done the trick for me several times.

Oh, I have had no luck using anything other than STP for this, I do not know why.

UPDATE 28 August 2024

Had surging problem again after above written and this time, air leak at intake manifold.