Drips at the Carburetor

updated September 17, 2019

Two stroke engine carburetors will drip fuel, especially when at or near idle.  Some will drip much more than others.

This is because a 2-stroke engine "spits" at the carburetor.  This is caused by the rapid opening and closing of the reed valve.  A small amount of fuel is forced back out the carburetor, hitting the choke butterfly valve, running down the choke valve shaft, and out.  As the engine speeds up under load, the back-pressure wave from the reed valve has less time to reach the carburetor opening so fuel leakage is less.

Sealing the air box flange with RTV cement, for example, will only help a little.  Thankfully, fuel leakage is only annoying but it is not harmful or dangerous.

If an engine has hundreds of hours on it, the carburetor can be worn out.  In particular, the throttle valve shaft bushings may be worn out and the carburetor will leak air and/or leak a lot of fuel.  The another part of the carburetor that wears out is the inlet valve needle seat.  Both of these issues require that the carburetor be replaced.  These problems are discussed on this page.

2-stroke engines are messy and inefficient – but we like them anyway because of their high power output to weight ratio.

However, if there is a leak between the carburetor and the reed valve body, the fuel pump in the Top 80 will not function properly.  You must be certain that you do not have this particular type of leak.