Shared Knowledge


Small Gasoline Engine Primer Bulb


11 November 2006

Updated: 7 August 2017



Summary: The primer bulb pulls, sucks, gasoline out of the tank and shoots it into the throat of the carburetor (carb). If no gas appears in blub after pumping it many times, either the bulb has a crack and is leaking or the hoses from the carb to the gas tank are cracked or the rubber gasket under the primer bulb is bad. Replacement of blub and gasket are easy do-it-yourself (DIY).







Most cubic centimeter (CC) size engines (chainsaws, weed eaters, leaf blowers) have primer bulbs.


The primer bulb suck gasoline from the tank via a hose and shoots it into the throat of the carb AND ensures that the hose from the tank to the carb is actually full of gasoline.


Shooting gasoline into the carb throat reduces the number of time you have to pull the starter rope.


The primer bulb does not pressurize the gas tank.


Holding the primer bulb in place to the carb is a metal flange held in place by 4 screws.


Under the metal flange is a rubber gasket with 2 small valves as part of it.


When you push down on the primer bulb, the valve going to the gas tank is closed and gas is pushed through the other valve into the throat of the carb.


After being pushed down, the primer bulb returns to its full size and in doing so, sucks gasoline out of the tank into the blub.



No gas in primer bulb:


After pushing down several times on the primer bulb, if the bulb is not full of gasoline:


1. The primer bulb has a crack in it and is not sucking gasoline out of the tank. Should be obvious crack in blub.


2. One or both hoses from the carb going into the gas tank is cracked or broken.


3. The rubber gasket between the metal flange holding the primer bulb in place and the carb is bad.


Primer bulbs, hoses and rubber gaskets are for sale from equipment dealer, eBay and other.


I do not sell parts for or service small engines.



Ron - Shared Knowledge Home