Unloading problem

[Paul Taylor]

I tried to sneak in a few flights at the end of the day standing in a flooded field. I am running a LA 46 burning 5/22 turning a 11x4 APC. Launched at 9540. Engine picked up a few hundred rpm and was too fast.  Second flight bumped it to 9450 and about the same results.

Was thinking about trying a 12 1/4x3 3/4 APC??

What say ye?

[Dave_Trible]

Paul,  hard to say sight unseen but sounds like you aren't getting enough air in the tank.  I'd hope the tank is uniflow and I've never had great results with muffler pressure.  I'd run open air and be sure your uniflow line isn't kinked or otherwise restricted.  Weighting the engine with too much prop will just cause it to run too hot and might actually make the issue worse.  Unloading is normal but getting a slight positive pressure in the tank will control that,  all else being OK.  Might also check for head leaks.

Dave

[ray copeland]

Paul, i just recently had the same problem on my new profile chipmunk. I finally figured it was fuel foaming, an additional strap around the tank fixed it. Just a thought, good luck.

[Paul Taylor]

Thanks guys. 
Ray i checked the tank and its goodN-tight.

A little more info. I am using a clunk tank on muffler pressure. Might try it with out pressure?

[Dave_Trible]

Thanks guys. 
Ray i checked the tank and its goodN-tight.

A little more info. I am using a clunk tank on muffler pressure. Might try it with out pressure?

Yup.

[Will Davis]

Paul,

I had similar motor runs on a Brodak p 40 last week, la 46 , thunderbolt plug, clunk tank, sig 10/22. 1/2 syn, 11 5 wood prop

Changed the prop to 12 4   Apc. With narrow blades,   All is well, it will be at Brodak's,

I think the engine was just in a unhappy / harmonic  induced vibration at that  rpm with too much prop and incorrect pitch for the engine rpm

[Paul Taylor]

Thanks Will
I have a prop to try as well.
See ya in a few weeks!