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, you may have another problem.
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 carburetor
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 will not
idle properly and may be erratic 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. PLEASE NOTE crankcase pressure
nipples are not recommended for throttled engines. At idle
pressure fluctuations cause the mixture to lean out after
10 to 20 seconds as the higher pressure in the tank is not
maintained and in turn the fuel line pressure drops.
If you can get
the engine running at idle squirt some 30wt motor oil around
the back cover, where the carb is mounted to the case and
the retention bolt or draw bar for the carburetor. You may
notice a change in Rpm's as the oil seals the air leak. Now
you can take appropriate action to correct the problem.
If none of this
works and you don't have base compression the clearances between
the crankshaft and crankcase may be excessive. On outboard
engines this could be between the PTO shaft and the PTO cover.
This is usually caused by running bad or worn out bearings.
This is the worse case scenario and usually both parts need
to be replaced.