Tower Hobbies 46 running too lean in the air

[DEADSTICKDAN]

Hi everyone,

I have a Tower Hobbies .46 engine that "acts" like it is running too lean in the air. By this I mean that it spits thick black oil all over the plane, it wants to quit, the cylinder head is piping hot after landing, and it does not have much power in the air. It is currently powering my Hobbico Brightstar 40. On the ground, I make sure it is running rich (11,500 rpm with an 11X6 wood prop), as it spits out quite a bit of light brown oil and smoke. However, after being in the air for about 2 minutes, the exhaust trail disappears, it loses power, and wants to quit.

I have replaced all fuel tubing (including brass tubing) to rule out air leaks in the tank setup, and I have a new tube running from the remote needle valve to the carb. I also leak-tested the fuel tank while submerged under water, and it was fine. There are no bubbles in any of the lines whether at idle, high rpm, or anywhere in between. Nor does the engine slow down when I hold the plane vertical. OS, Tower, and Fox glow plugs do not solve the problem.

I disassembled the engine, and found that there is no visible evidence of wear (grooves or shiny areas), so this engine is not grinding itself to death either.

This engine, in this plane, used to spin a Master Airscrew Nylon 11X6 prop at 13,400 rpm! A while ago, I switched to a Top-Flite Powerpoint wood 11X6 prop, since it was recommended by Tower in the instructions. Could it be, for some reason, that since the wood prop is lighter, it causes the engine to run hot? I don't have that nylon prop anymore, but I will buy one to try it as a last ditch attempt if anyone thinks this may help.

Thanks!!

[Dave Robelen]

Hi DEADSTICKDAN,
The first thing to check is the compression, both cold and warm. If that goes OK, then start the engine and run up to about 1/4 throttle with the booster clip left on. Pull the booster and note if the RPM's drop. If the engine slows down, there is a problem with either the fuel or plug. A K&B plug is usually a very good match for that mill. it is nice and hot. The other possibility is the fuel. Your description of brown goop sounds a bit like contamination in your fuel. Or it may have sat too long uncapped and lost too much nitro. If possible, borrow a tank of something like 12% fuel with some castor oil that is running good in someone else's mill.
Usually, this type of problem has to do with leaning it out on the ground to compensate for poor ignition, and then in flight it gets still leaner and quits.
Good luck, Dave

[DEADSTICKDAN]

Thank you, Dave. I will try your suggestion and let you know if it works.:)

[chris fabbro]

sounds like you need a smaller prop because an engine will
overheat when its trying to pull one thats too big. I have a
46 like yours and noticed that the engine got pretty loose after
a few flights (less compression) and this translates to less torque
but will still turn some rpm if the right prop is on. Try a 11-5
or a 10-6/7. later chris

[DEADSTICKDAN]

Thank you for your help, guys. The problem was in fact the propeller! When I was having success with this engine, I was using the Master Airscrew 11X6 nylon prop. Problems began to arise after switching to a Top Flite Powerpoint 11X6 wood prop. One member of my club suggested that the airfoil of the Top Flite prop may have been different enough to overload the engine, so, if I were to go with this manufacturer, I should try an 11X5. But, sticking with the Master Airscrew 11X6 nylon led produced 13,100 rpm this past weekend, and a docile airplane became a rocket ship!!