Frequently Asked Questions (FAQ)
My engine runs for a few minutes and then quits.
When an engine only runs for a few minutes and then quits, it can be one of the most baffling problems for a modeler to solve. Resetting the needles, changing glow plugs, trying different fuel, even replacing the fuel tank and its plumbing doesn't work. The engine still runs only a few minutes and quits. For an airplane flyer, this means dead-stick landings and possible airplane damage, and it costs races for the car guys.
What causes this?
Basically, the cause is engine overheating. Because the engine runs normally for a while before it quits, the overheating is gradual. You can have good fuel and a good needle setting, but still have the problem.
Gradual overheating is most commonly caused by the exhaust system. If the exhaust system is slightly restrictive, the engine won't be able to 'breathe' freely, and it will retain a little bit of heat each time it fire. Eventually, the heat will build up to the point where the engine quits. Restrictive exhaust systems are usually the result of using mufflers, pipes, and headers that are not provided by the engine manufacturer, but are made by third-party manufacturers.
Another source of gradual overheating is an exhaust system that will not allow enough pressure to be developed so that the engine will have good fuel flow. In order to solve the exhaust restriction problem, the muffler system becomes so free-flowing that too little pressure is developed to pressurize the fuel tank enough.
Mufflers and exhaust systems are usually made in only a few sizes, and then adapted to fit a wide variety of engines. For example, one popular manufacturer makes a "Pitts" style muffler for a wide variety of engines. The main muffler body and exhaust pipes are the same, but the portion that attaches to the engine's exhaust port is different, depending upon the engine it's to be mounted to. It works very well for .61-size engines, but is a bit restrictive for .91-size engines. The .91-size engines will tend to gradually overheat and quit.
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