jmess73

I have a tufflight predator with a magnum 40 on it, because of the location of the tank I believe the engine is having a hard time getting fuel. It will run perfectly sitting flat, but when pointed up it wants to quit and die. If i richen the mixture up a couple of clicks, it runs rich flat, but perfect when pointed up. Also when the tank approaches empty it leans out some more. I've never had these problems on any of my other planes, but on this one the fuel tank is pretty far away from the engine. Also I forgot to mention that the engine is almost all the way to the front of the mounting rails and that the centerline of the fuel tank is even with the carb inlet. Is there a simple fix I don't know about, or how about adding a fuel pump of some kind.

Jeremy

Lou Melancon

JMess73,
It does sound like your engine is having trouble drawing fuel. A low fuel draw can often be traced to leaks in the overall system reducing the overall ability of the carburetor's venturi to draw fuel. Some things to check are the seal of the carb to the crankcase, you might need to seal it with clear silicon; also Magnums often leak through the o-ring seal on the carb and you may have to put a piece of fuel tubing over the needle to get it to seal properly; the seal of the fuel tank is also something to check you need to make sure it is not leaking which you can check by pressurizing it and holding the pressurized tank under water to see if it leaks, and finally check the fuel line when the engine is running to see if it has bubbles in it - these would be caused by vibration causing the clunk to jump up into the top of the tank and suck in air.

If all of the above check out ok you might consider some type of pressure feed system. A bubbleless tank like Jett Engineering offers or a pressure bladder would solve your problems. The pressure bladder is the cheapest solution but has a learning curve associated with it plus you will need syringes to fill the bladder. Good luck.

Montague

I agree, it sounds like you have an air leak in the fuel system somewhere.

jmess73

Thanks for the advice, I resealed the carb, and added fuel tubing over the needle valve and its better. I still need to run it a little rich, but I tried overproping a bit and this seemed to help. My top end suffered a little but it runs smooth.

Jeremy

jmess73

I put a new engine on it, a Magnum XL 28A RNV, all my problems have gone away, I guess that old engine was just a little tired.