Most of the time
the problem of engine not starting can be traced to a bad
glow plug, low battery for the glow plug (1½ volts)
or bad fuel... but if you checked those items, or you can't
get fuel to draw unless you put your finger over the venturi,
you may have another problem.
Check the orientation
of the spray bar. The spray bar has a small outlet hole to
atomize the fuel. This small hole must be pointed straight
down into the venturi. If it is pointed to the side or you
can see it looking into the venturi, it will not draw fuel.
Note: Some Fox engines had 2 hole and must
be orientate side to side. Not a good design.
A 2 stroke engine
requires a good seal in the crankcase to run properly. As
the piston goes up a fuel/air mixture is drawn from the venturi
into the crankcase, usually through a port on the crankshaft
on most model glow engines. As the piston goes down the port
closes and fuel/air mixture is compressed in the crankcase.
This is called base compression. When the piston nears the
bottom of the stroke the exhaust ports open in the cylinder
then the cylinders inlet ports open, the fuel/air mixture
is blown into the cylinder clearing the remaining exhaust
and supplying the new mixture for combustion.
If there is a leak
in the crankcase, the engine may not start or draw fuel. If
you have a leak, as the piston goes up it will not draw sufficient
air through the carburetor to create fuel draw. If it is a
small leak you may get the engine started but it may run erratically
at higher RPM's.
You can check your
base compression by removing the glow plug and turning the
engine over in
the correct direction. You should feel slight compression
as the piston goes down and hear a "puff" sound
as the ports open in the cylinder. If you don't, try to determine
where the leak is.
If you are using
a crankcase pressure tap, be sure the line to the tank is
good and the tank is not vented. Plug off the nipple off while
checking base compression.