Greetings 4-stroke gurus,
I am having a problem with a Thunder Tiger S54 4-stroke engine. The engine runs fine on the ground, taking off, level flight, inverted flight, even during rolls. The problem comes when in a high G situation like flying level then entering a loop. The engine dies immediately. [&o] Pulling the plane up to vertical slowly seems to have no affect and continues to pull the plane up. I have relocated the engine to a level where the center line of the carb is just below the top of the tank. There are no leaks in the tank or associated tubing. The tank sets within 1 1/2" of the back of the engine. I run 10% powermaster fuel and run an 11 x 7 prop. I have replace the needle valve "O" ring and checked the valve settings. I can find no detectable air leaks. Does ANYONE have a clue as to what my problem might be?

Sonnytex

The center line of the tank should be even with the center line of the needle valve.

w8ye,

Humm, that would be impossible on this plane as I have the engine as low as the firewall will allow the motor mounts to go. I have the same plane with an OS 46AX on it too and the carb is higher than the tank and it flies great. Seems to me that if I could lower the 54 any more the tank would syphon into the carb.[sm=spinnyeyes.gif]

sonnytex

Could it be that your clunk is too close to the rear of the tank? If the abrupt pull-up forces the clunk up against the rear wall of the tank it could cut off the fuel flow momentarily. Sounds like the carb is near the center of the tank, depending on the tank dimensions.

BTW, what's the RPM with that 11x7 prop?

CR

Charlie,

Clunk too close to the back of the tank - that is a good thought but I did check that although I failed to mention it in my original post. I have had the tank apart three times looking for a problem. Thanks for a good idea. It has been a while since I checked the actual RPM
with the 11 x 7 prop but I remember it being somewhere in the 8800-9000, perhaps a little higher when leaned out to the max.

sonnytex

<font color="#0000ff">Any other ideas?  I have a similar problem with my TT F54-s (airbleed carb version).  Except I can sort of reproduce the problem on the ground by flipping the plane up-side down with 3/4 -full throttle and manuvering the plane by hand as if it were doing a loop.  It looses rpm, smokes more, then dies.  The fuel line remains full of fuel.  These signs would indicate that it is running too rich when moving inverted.</font></p>

<font color="#0000ff">-Walt</font></p>

Walt,

No new ideas - I finally set that sucker up on a shelf - life it too short trying to figger it out. By the way, mine would run fine right side up, upside down or any position in between. It would just die when trying a high G manauver like pulling into a tight loop. I put an OS .61 on the same plane and it runs great. Hope you find your problem.

Sonny