Small Engine Troubleshooting

Small engines are very touchy with their tuning. EPA regulations have made small engines run much leaner than they have had to in the past. This will make the engines run cleaner and be more fuel efficient, but generally don’t run as well. Also if the carburetor has any build up in it the engine will be too lean and will surge. To compound the problem most new carburetors are non adjustable due to EPA regulations. Most small engine carbs have a high speed and low speed circuit to control the fuel. When you hear an lawn related engine surging it is almost always lean. If the engine is older, the carb screws on it’s side may be adjustable. You need to locate the main circuit or high speed screw that usually has the letter H along side it. This screw is a fuel control screw that will have a spring under it. As you turn the screw out it delivers more fuel to the engine. Don’t turn the screw more than 1/8 of a turn at a time then wait a few minutes before changing again. The engine should smooth out and the setting should stay there.

 

If the screw is turned out too far the engine will run rich, burble, misfire and consume a lot of fuel. Newer carbs with blocked adjustments should be tuned where they need to be. Newer carbs probably have build up problems internally that are restricting fuel flow. Another reason a small engine could surge would include an air leak in the intake side of the engine. You could spray carb cleaner on the gaskets and intake when the engine is running. If there is a leak, the engine should rev up or bog down quickly when being sprayed. The governor system could also cause the engine to surge. The governing system usually uses an air vane with a few throttle linkages to control the amount of power being delivered to the vehicle. The engine power will be limited until the engine is being bogged down then the governor throttle will open to make more power. Go cart owners will often stiffen or shorten this spring to hold the throttle plate wide open to deliver the full power of the engine. The governing speed is a very touchy set up and should not be messed with unless your confident about what you are doing.