Guys,
I have been fighting a setting problem on my OTS Ringmaster with an old OS 25 baffle motor. The motor has very good compression, starts with one flip, has no shaft wear, should be great. The motor run is all over the place, sometimes way lean, if I open it up it goes sloppy rich then comes in late in the flight. I have checked for dirt in the NVA (none), changed filter, plug and fuel (even tried Byron fuel) same result. I am going over the motor and checking for air leaks around the NVA found none. Last hope is to check tightness of head bolts and backplate (there is some spot of baked oil on the head).

If none of the above work out I want a Plan B - change the motor and tank. I have a fairly new OS FP 25 and 2030 muffler and a Hayes 3 oz tank. I have read the posts on this setup and seems a 9x4 prop at around 10K should work. Question is how is the tank setup for the muffler pressure? I understand to mount it with the "foot" down, that would put the two vent tubes at the top, that's OK. To hook up the pressure line do you just use one of them and cap the other? How does that work on outsides and inverted? Or do you add a curved tube to put the vent to the inside edge and keep it open? A picture would be a great help.

Thanks,        DennisT

My understanding is the set up for the Kraft Hayes 3 oz tank out there is suction, not pressure.  Check me on this.  I think this tank is no longer available.  If you want a plastic clunk tank with three holes in it that you can set up for presure the Hangar 9 one that came with the PT 19 is about the same size.

Look for bubbles in your fuel line when the engine is running.  If you see them you have a leak in the tank.  More than likely you have a vibration a problem.  Try some foam under the tank.  You may have a weak nose.  Vibration is evil.

This looks pretty available to me: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXK826&P=7.

I drill out the vent, put muffler pressure into the lower vent, fill into the muffler pressure or the fuel feed line, and cap the upper vent for flying.  On an FP 20 and a LA 25 I get wonderful engine runs.

Ok good to know.  Thanks Tim

You are running a filter between tank and needle valve, yes?

Not running a filter can cause all sorts of odd engine-setting problems that just go away as soon as you stick a filter in there.

Your problem is vibration/fuel foaming.  Armor all in the fuel, foam rubber, these are some options.  Your old OS is probably fine.  You have seemed to eliminate all the other issues.  Run the old OS with the tank on the test stand.  Look for bubbles in the line.

Vibration is a beast and can be pretty deceptive.  In worst case situations you will not even get a needle, let alone a good run.  You will spend hours looking at the tank/engine when the problem is right under your nose.

you could ignore the nva set up..

I don't know why Dirt likes to use multiple needle valves.  But I use the (one) remote needle valve that came with my FP 20, and the only problem that I ever had with was that normal sized fuel tubing would slip off at highly inconvenient times.  But I have never, ever, had that needle get damaged in an inverted landing -- even over pavement.

Yes, there are slight handling and consistency advantages to using a regular needle valve.  But they're teeny compared to getting the tank set up right and using a filter and all that other essential stuff.  So if you're still in your "Sir Crashalot" stage, I highly recommend the remote needle.

Dennis:

The manual that I have for that engine says that it wants a 9-5 or a 10-4 prop; part of your problem may be that you have too much prop for it.

I know I'm harping on this, but you didn't mention the fuel filter -- if you're not using one, get one.

Guys,
I pulled the engine off the ship and checked for leaks. I think I found it. Seems the exhaust flange was not even, the bottom edge had some slight unevenness. The rest of the engine was tight. I reinstalled the muffler with high temp sealer, will test later today. If it still is inconsistent I will pull the muffler pressure. Hope this works I'm off the KOI.

Best,          DennisT

On rare occaisions a particular engine/model (not model design) combination will set up a harmonic imbalance that will cause (bad) vibrations as the engine rpm's go up in flight. Looks good on the ground, goes wacko in the air! Change the engine!

W.