Real2You

Hello,
I bought a swap meet airplane that had a KB 61 on it and I just can't get it to run right. It will run great on the ground but once in the air it flies a few minutes then dies. Anyway, I would like to replace the engine with another new engine but I can't seem to find another engine with the same mounting dimensions. If I change the mounting bracket it will require cutting the whole front of the plane up. By chance does anyone know of another engine with the same mounting hole configuration? Thanks.

Real2You

I forgot to mention...I would rather not put another KB 61 in it unless I could find one new.

the Wasp

My Feedback: (1)

what prop? what glow plug? what fuel

this may not be a big problem. an engine can act as you describe if it is not loaded well with the prop that is in-use.
if you are swinging a 10 inches prop or smaller, please try a 11x7, 11x8, or a 12x4,12x5 and re-tune.
it could have an old O-ring doing strange things when it gets hot.

questions: are you sure its compression has not been increased?

Jim

049flyer

My Feedback: (18)

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.

049flyer

My Feedback: (18)

Real2You:

Another common problem that often causes the issue you are having is a pin hole in the bit of fuel line INSIDE the tank. As long as the pin hole is submerged in fuel the engine runs fine, but once you burn fuel below the hole it begins to admit air into the fuel stream, causing the engine to lean out and die. Whenever I buy a used plane or pull one down off the wall that hasn't flown in a long time, I always pull the tank out and replace the fuel line from the clunk all the way to the nipple on the engine. Good time to check the condition of the foam around the tank too.

As you can see there are a lot of problems that can be the fault of the aircraft fuel system and not a problem with the engine itself. Installing a new engine may not fix your problem but will certainly lighten your wallet.

Real2You

I'll have to check the prop and the fuel system. I really didn't give all that much thought because it ran good for a few minutes or so before it died in the air. It actually did it 3 or 4 times before I took the engine out and tried to replace it with a OS 65( I think it was). All of your guys replies make sense. I'll go back to square one and check the padding around the tank, fuel line inside the tank, height of the tank all of the suggestions. Thanks guys I appreciate the advice.

the Wasp

My Feedback: (1)

hey. you know. you may just happen to have a rather cold plug in it ?