.. tank wizards...

[Bootlegger]

   Mornin Guy's
  I have a question for the "tank wizards" of the Stunt world.  I have a clunk tank 6oz cap that is set up uniflo open to the atmosphere and it runs away after the three inside loops, Doesn't come back at all. Fuel is 5% Powermaster engine is an OS 32 SX w/ hemihead, blocked boost port Tbolt idle bar plug APC 10x5 prop.
  I have an identical set up on another profile that is very consistant. I have changed tanks to the consistant one as of this morn. Three of my flyin pals have all said they think it is the tank.
  I am gonna try this set up next, does anyone else have any suggestions.
  On the other profile this engine runs like a champ, so I am at my wits end...  HELP...

[john e. holliday]

I had similar setup on the new version of the Ringmaster years ago.  Would fly rich until you forced it thru a loop, then 2 cycle the rest of the tank.  Finally put it on muffler pressure to solve the problem.  DOC Holliday

[Garf]

All it takes is the smallest pinhole to do what you are seeing. Have you pressure tested the tank?

[Bootlegger]

  Guy's this is a plastic clunk tank, sorry that I didn't put this in the post.
   Sure do appreciate the help, and I will check for pin holes in the tank and tubing.
  Again, Thanks Guy's...

[Wynn Robins]

yep - check for holes - that is what it will be.

[Tom Perry]

You might want to make sure you are not over propped.  If fiddeling with the tank doesn't help try a 10-4 and see if any change.

[Alan Hahn]

I'm guessing it's the engine. I know you think you have the same setup that works perfectly on another plane, but all engines have tolerances (and different levels of break-in). Also you may have a resonance in this plane that foams the fuel.

We wait for your next test. I wouldn't be surprised to see that it still runs away.

[Bootlegger]

  Alan, I did change the engine to another OS 32 SX and still have the same run away when I start into the three inside loops.
  I have changed the tank and hopefully will get to fly later this week.
  I will keep everyone posted as I too am curious as to what the problem is.
 I am gonna add some Armor All to the fuel ro see if it is a "foaming" problem.
  Sure do thank all you fellows for thr suggestions and help...

[Bootlegger]

    Well I have done all the things that I can come up with and the suggestions that ya'll were so good to suggest, but  It ain't helped, went flying this mornin and still have the blasted run-away's.
  The engine is bolted to some 3/16" plates and the plates are bolted to the airframe, got it started this mornin, nice soft 2 cycle for about 1-1 1/2 min. then sitting on the ground it wound up, opened the needle about 1/2 turn and still runnin hard.
  Stopped engine and when I picked it up I almost burned my hand touching the alum plates.
  Is it possible that these plates are transfering heat back into the engine and overheating it to the point of run away???
  My next thought is about figurin another way to bolt the engine down.
  As ya'll know it had a Merco 35 on it but it didn't have quite enough uumph, that is why I went to the OS Max 32 SX that runs so well. I even changed engines !!!
  My thinkin is if I have an air leak why doesn'y it run hard when first started
         HELP...HELP..

[Just One-eye]

I was used to having an FP 40 of mine want to run faster and faster the longer it ran, until one day I used the "wrong" fuel.  I filled it up with the 25% oil mix that I use with my "iron" engines, about half and half castor/ synthetic.  The needle setting was off, but very easy to find a new setting, and that much oil kept it so cool-running that it never tried a "runaway" again as long as I fed it this oiliest fuel . .

[Mark Scarborough]

My first instict tells me that if it runs away in manuevers it is running on the ragged edge of to lean,, or it needs more oil. Castor that is, pure bean oil, that should help. However this is after you have elimnated the pinholes, tank plumbing, and clogged filter or needle.

However, you said you have tried two engines, and both have the same problem? I would say you need to look for something on the plane that is causing it, say resonating. are you sure the bolts dont bottom out when you bolt the engine on? is the wing to fuse joint SOLID.
 I still am inclined to try oil as was suggested in one earlier post.
My FP 40, and one of my LA 46 engines, dont like to run steady unless they get to drink some extra castor. I use Powermaster GMA 10 22 but I add about 6 oz of castor to a gallon, and it absolutely cures my runaway woes.

[Perry Rose]

   Gil, is the clunk too close to the end of the tank?? I had similar problems this week with a plastic tank, tried all the above and later found the clunk at the tank end. I cut a half inch off the clunk tube and solved my problem.
Perry Rose

[Bootlegger]

  Perry, The engine starts and runs real good for about 1-2 minuets, then it runs away, not when first started like a hole somewhere.  I took the tank off and pressured the tank and all tubing as well as the filter NO LEAKS...!! This has me buffalowed, also no bubbles in the fuel tubing.
  The fuse is 3/8" thick and the m/mounts run back to the l/e of the wing top and bottom, 1/64" plywood down each side nose to tail with 1/16" doublers and 1/4-3/8 balsa doubler on the inboard side.
  Never had a problem like this...
  As for the clunk, it clears the rear end of the tank freely.
  Guy's this really has me stumped...
   The capital letters are for emphasis nuttin else...
       Again thanks for all the help, Gil   HELP...

[Bill Adair]

Gil,

A closer look at your tank plumbing might help. It almost sounds like the tank vent is plugged, and a slight drop in tank pressure occurs as fuel is drained from the tank. That would also explain why opening the needle doesn't richen the mixture. A blockage in the vents would not show in a pressure test.

I'm not sure if a prop slip stream can reduce pressure in a tank, if it happens to cause a slight negative pressure area at the tank vent? I see lots of recommendations to route uniflow vent lines into clean air on the inboard side of the fuselage. Must be a reason for that.

If it were mine, I'd connect the uniflow vent to muffler pressure, and see what happens. If it doesn't run away on the ground, try a short flight.

Good luck.

Bill

[Bootlegger]

   Bill, I'll sure try that next, as far as the vent being plugged I'll check that also, but with the uniflow open to the atmosphere the engine should continue to run in a stable condition, or steady condition, because it is a vent. Also shouldn't fuel go into the venturi when filling thru the uniflo and the vent being stopped up?
  This thing has me stopped up !!!
  Guy's I sure do appreciate all the suggestions, and PLEASE keep them coming as together we can solve this problem...

[Bootlegger]

     Found the problem... It should have been caught more quickly than it was... (Drum Roll)......BAD FUEL... opened some fresh fuel and all is well in the world now...
         Again I sure do appreciate all the suggestions...

[Bill Adair]

Gil,

Glad you found the problem. 

Bill