Model Engine Company of America
Cause of not starting, no fuel draw, no low RPM's


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.



The above information is provided as a guide. Since MECOA/K&B has no way of determining the ability of the individual using and understanding this information, we assume absolutely NO RESPONSIBILITY for any damage to person or property from the use of this information.

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