Engine will run, but it surges, hunts for a constant RPM

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1. Partial Blockage of Main Jet. This is for bowl type carburetors only. Stop the fuel flow to the carburetor, either turn off the fuel valve or pinch off the line with a pair of fuel line pinch off pliers or a pair of vice grips. With a pan suitable of containing gasoline, loosen the fuel bowl nut and catch the gas. Now remove the bowl nut and the bowl. Blow out the holes in the nut with compressed air or carburetor cleaner. Some Tecumseh carburetors have a tall bowl nut. Some will have a pin hole in the side of the nut, and some will have a pin hole just above the bottom set of threads. This hole must be clear in order for the engine to run properly.

For engines that do not have the jet made in the bowl nut (Kohler, Kawasaki, Honda, some Briggs and Strattons, Onan, Wisconsin-Robin) the jet is attatched to the center post of the carburetor. Some are cast in and others are screwed in. Blow this hole out and blow up the center post to clean the main nozzle. Use compressed air or carburetor cleaner.

For all down draft Briggs and Stratton Flo-Jet carburetors (7, 8, 10, 11 HP Horizontal), remove the bowl nut (has adjusting needle in it) and blow compressed air up the nozzle. For Opposed Twin engines, Horizontal and Vertical, remove the bowl drain nut and blow air in that hole.

2. Leaking Intake Gasket. Check for a loose carburetor or mainfold connection at the block. All Briggs and Stratton engine 3 to 6.5 HP, check the intake manifold for cracking (may have to remove carburetor) or loose connection at the block. You will need to remove the air shroud to get access to the intake manifold.