Fuel Tanks
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So you are having problems getting your engine to run. Join the club!! Tank and carburetion problems are the most common of all. People often call asking for head shims because they are burning plugs. You burn plugs because your engine is lean, and very seldom because it needs head shims. Heads are set at the factory and should be correct for almost all conditions.
Three things mostly cause lean running: bad needle settings, air bubbles in the fuel lines, or the tank is mounted too low. (See the engine instructions and our paper on setting r/c carburetors for setting the needles)
First of all, get that engine out of the airplane and on to a test stand. If you have installed a new JETT engine, which was tested at the factory, then chances are the problem is in your airplane. Even if it was running ok with your former engine and you are certain all is ok, you must get it on to a test stand to eliminate all those variables. If you send it back to me, I will just put it on the stand, and if it is ok, then I will probably charge you for the trouble. Check it out!!!!!!
Tanks: We really can’t cover this enough. Your tank must be perfectly isolated from the airplane. It cannot touch anything but foam, and lots of it. Wrap the tank on the top, bottom, sides, front and back with at least ½” (10mm) of good dense foam. Clean the tank thoroughly, replace the tubing inside and out and check for leaks. Use at least medium size tubing.
Tank location is critical. The centerline of the tank should be about on a line with the centerline of the needle valve, not on the centerline of the engine. The recommended way to mount an engine is sideways because it solves most of your tank height problem. It you mount the engine upright, then the tank will have to be raised somewhat. If you mount the engine inverted, then you will have to lower the tank considerably to prevent the tank from flooding out the carburetor.
The tank should be as close to the back of the engine as possible to prevent draw problems during long vertical climbs and flooding problems during long vertical dives. The distance is not really the problem; the relative height of the tank vs. the carburetor is the problem.
When it is not possible to locate the tank in the preferred spot you may wish to try a 'hopper" or booster tank. This is a small tank located at the correct height just behind the engine, which is in turn connected to the larger main tank. The connections are simple. Connect the outlet (fuel) of the main tank to the inlet (pressure) of the small tank. Connect the pressure of the main tank to the muffler. Connect the outlet of the small tank to the engine. Fuel thru the engine feed line, and overflow thru the muffler, as you always do. This tank system tends to reduce the negative effects of an improperly located main tank.
Pumps: pumps and regulators have the potential of solving many of the above-described problems. However, they are added complexity, which should be avoided if at all possible. Jett does not recommend any particular type because each application is unique. Some have had great results, but others have not. The best path is to avoid installation situations, which require such unusual solutions. If you do install a pump, please call the pump manufacturer for technical support.
