Why is my Engine Hunting?

If you’re reading this, the chances are that you have a small engine that is revving up and down, formerly known as, hunting.

Hunting, is a term given to an engine that is surging up and down in a regular cycle. It actually means the engine is hunting for fuel.

Why does it Happen?

There are many reasons as to why an engine will hunt. The most common reason is that the carb is partially restricted, meaning an insufficient amount fuel is being passed through to the combustion chamber, causing the engine to slow down. In order to rectify this, the engine’s governor opens up the throttle butterfly, forcing more fuel into the combustion chamber to speed the engine up, and as such the governor then closes the butterfly to slow it down. This cycle repeats and causes the engine to constantly hunt for more fuel.

This essentially means that the engine is running way to lean. You may also find that by partially closing the choke, the engine will smooth out. This is because you’re reducing the engine of air, and balancing the air/fuel ratio. This is not a fix. The engine will still be running way to lean, and you may also notice popping and the muffler getting very hot. More information on engines running lean can be found on our Having Carb Related issues? page.

Governor Linkages & Weak Springs

Although less likely, governor linkages and weak springs can also cause the same symptoms. If cleaning or replacing the carb doesn’t fix the issue, checking and replacing these may well rectify your problem.

Vacuum Leaks

Check to ensure your gaskets are all intact. If a gasket is broken or intake manifold cracked, then the engine will be sucking in too much air, and not enough fuel, leaning out the mixture and also causing your small engine to hunt for more fuel to balance out the air/fuel ratio.

Can I do this repair myself?

Diagnosing and repairing this fault can be daunting task for even the most competent DIY mechanic. Unless you’re highly experienced in dealing with this problem, it’s probably best to pass the problem onto a small engine repair shop such as ourselves or you’re preferred local small engine shop. They’ll have the ultrasonic cleaning machine to properly clean the internals of a carb.

Basic things to check that may well fix the problem

• Is the fuel filter dirty?
• Age / Condition of the fuel
• Is the fuel line kinked?
• Is the fuel pump working if fitted?
• Are the gaskets intact?
• Is the carburettor clean?

Here’s a helpful video, courtesy of Dave’s small engine saloon: