Chain Saw Parts: Engine RPM's surge up and down
If your chainsaw engine RMPs surge up and down, start by checking the gasket, insulator, and O-ring. For more help on identifying your problem and questions on how to fix it, follow our repair guide. Note: this is a general repair guide. Check the manual provided by your owner for more specific repair information related to your model.
O-Rings
A bad O-ring seal between the carburetor and the engine will allow extra air into the engine and cause a surging condition. As with a damaged gasket or insulator, the extra air that leaks in through the damaged O-ring will be unregulated, so rather than creating a steady high-RPM situation, the RPMs will surge up and down uncontrollably. You will need to replace the damaged O-ring as soon as possible, because the extra air will prevent the engine from being properly lubricated, and this can damage it.
Gaskets
The carburetor regulates the ratio of air and fuel that enters the engine. If extra air enters the mixture after the carburetor, the ratio will become lean, which will increase the engine RPMs. This air can enter through the gasket on the carburetor if the gasket it loose or damaged. Because the air doesn't enter the engine in a controlled or consistent manner, it will cause the RPMs to surge up and down depending on how lean the mixture is at any given moment. This can cause serious engine damage because of a lack of lubrication. The gasket will need to be replaced to create a proper seal, and ensure a consistent air/fuel mix. ... Read more
Insulators
The insulator is a plastic block that mounts between the carburetor and the engine, and insulates the carburetor from engine heat. If the insulator is cracked it can let extra air into the engine, causing it to surge. When there is too much air in the cylinder, the mixture is referred to as lean. If the insulator is damaged, it is important to replace it immediately as a lean fuel mixture won't properly lubricate a 2-cycle engine, and this can cause costly damage to the cylinder and piston.