Originally Posted by
Real2You
I forgot to mention...I would rather not put another KB 61 in it unless I could find one new.
Would it not be easier to get the engine you have running? The K&B 61 is a very good engine and normally very reliable, perhaps not as powerful as more modern engines but fine for sport uses. Besides if the cause of the problem is fuel system related then you will have the same problem with a new engine.
Sometimes this problem is caused by the tank mounted too low, the center of the tank should be even or slightly below the needle valve or center of the carb. If it's too low the engine will go lean after the fuel burns down (the engine will be drawing the fuel "up hill").
However, most of the time the problem you describe is due to foaming of the fuel. The tank MUST be mounted in a bed of foam rubber surrounding the tank on all sides, nothing touching the tank except for the foam. What happens is that vibration causes the fuel to foam up, just give your fuel jug a good shake or two and you will see what I mean. At first, while the tank is full there isn't enough room in the tank for a lot of foam to form, but after you burn up a couple of ounces of fuel the foam begins to foam and before long you are drawing foam (air and fuel) in through the pickup instead of just fuel. The engine leans out and quits.
Insulating the tank from all vibration with the foam will prevent the foaming. Another trick that works for our control line brothers is to add a couple of drops of Original Armor All into your fuel can. Usually a couple of drops will do it. Just try it! Shake your jug, note the foaming, add a drop of Armor All and shake again. Repeat until the fuel no longer foams or the foam goes away really fast. Usually it takes only 2 or three drops per gallon. Don't rely on this method alone! You still need to insulate the tank with foam.
But the best way to figure out engine problems is with the engine on a test stand instead of the plane. Then you can easily troubleshoot problems and try different solutions. Once you get it running good on the test stand then mount it on the airplane. Any problems you have from that point forward are related to the fuel system on the plane.