Riding Lawn Mower Surges at Idle

Is your riding lawn mower not working exactly like it should. Does the engine surge up and down when you start it up and idle warming up the engine? A constant rev up and down of the engine is called surging. It is like the engine gets some gasoline and then it doesn’t and slows down.

That is actually what the engine is doing. A small bit of gasoline comes into the engine and then it doesn’t receive any and then it nearly dies and then another small dose of gas arrives and then the cycle begins over again.

This is called a lean surge when the engine is not getting enough gasoline to air fuel mixture. A lean surge can be caused by the carburetor jets being plugged up or an air leak in the intake tract. Air leaks will cause too much air to enter the intake and reduce the vacuum pulling through the carburetor which in turn reduces the amount of fuel being pulled out of the main jet. Then the surging begins.

An air leak can be in the carburetor itself or in the intake manifold or where the carburetor connects to the engine such as an intake gasket leak. Check all these areas carefully to find any air leak before you go and pull the carburetor apart to clean and inspect it.