Priming is squirting fuel directly into the carburetor's
air/fuel intake stream, usually before cranking the motor. It helps with
cold starts by providing an
immediately combustible mixture.
Squeeze bulbs are commonly used. They have two one-way check
valves so that squeezing the bulb forces trapped fuel out the outlet
end. When released, expansion sucks new fuel in the through inlet check
valve. Both check valves must work and all fittings must be tight.
Possible problems include loose or deformed fittings, improper
installation, bad check valves or holes, . The bulb must be installed so
the outlet end is towards the motor.
(aka pumper) carbs like the Walbros, can also be primed by air vent
pressurizing. Blow in the fuel tank's air vent line which forces
fuel up to the carburetor under pressure. Insert a thin wire or other
object into the needle release hole. That pushes a fulcrum which lifts
the main needle valve allowing fuel to pass. Keep up pressure on the
vent line while doing pressing and fuel will squirt into the carburetor
throat. A WG8 carb is shown. Some have a button that sticks out so you
don't have to insert anything.
The last method is direct priming. Fuel is squirted directly
into the fuel/air stream between the carb and engine. This is usually
done by a pull/push pump where you pull the knob to suck fuel in then
push the knob in to force the fuel into the carb. Be careful because if
air leaks are present they won't be obvious and will dramatically affect
engine operation. If the fuel source is pressurized (even by gravity
such as those with a fuel tank above) then this system could also
potentially allow fuel to feed.
is the stock primer bulb that frequently comes with the Simonini motor.
It is prone to internal problems that let air bubble into the fuel. It
is common on Fly Products, Fresh Breeze and other motors.
replacement, found on many newer machines, appears to reduce problems.
Check with your motor's seller about availability.
Photos and bulb info by Adam Bell