Engine slows down on outside loops.

[Martin Quartim]

I have a Pathfinder with an Enya 45 6001 that Frank Bowman rebuilt  for me. There is one .026 head gasket, fox plug, top flite 12x6 sanded top, fuel with 10% nitro 10% castor %10 sintetic, Brodak Wide Wedge Uniflow tank.

The laps timing straight and inverted are the same. Engine runs solid as long I am not pulling Negative Gs. If I do the out side loops easy and high it doesn't seems to slow down.

when I come inverted and pull a normal outside loop, it imidiatelly slows down.

Seems it goes rich, and the harder I pull the slower it goes.

Any ideas of what I could do or try?

thank you,

Martin

[Larry Cunningham]

Are you absolutely sure it is going rich? An engine can slow down when it is going too lean
as well. Try going just a tad richer on the NV, and see how this changes things. During the
outside, If it slows LESS, it is going lean, if it slows more, it is going rich.

Engine mounting, venturi size, plug heat range, fuel tank design, fuel leaks, air leaks,
fuel filter, fuel line, base compression, NV orientation, muffler type, vibration, fuel oil
and nitro content, prop size and pitch, and probably another half dozen things can
affect mixture during maneuvers. Someone with experience with the Enya .45 may
well be able to steer you directly to a solution.

Or, you may have to meticulously troubleshoot these items (or something I didn't mention)
to find out what or what combination of things is causing the problem.

I don't want to discourage you, I wish you well in finding it. It is probably something simple
and dumb.

L.

"In character, in manner, in style, in all things, the supreme excellence is simplicity."
-Henry Wadsworth Longfellow

[Eric Viglione]

As I said "over there"...

Well, it's just a guess, but I see where your uniflo vent is, and think it could be breaking into the air stream harshly on abrupt outsides.

Take a piece of longer fuel tubing and try running your uniflo vent to a dead area, like tucked inside the concave back plate of the motor for one flight and tell us what happens. 

Eric V.

[Bill Little]

Another point is that equal lap times upright and inverted do not "always" ensure an equal engine run during manuevers. 

While you're trouble shooting, move the tank a 1/16th inch higher (plane on it's wheels) and see if the problem is helped.  It will, probably, slightly pick up speed for inverted flight, but many guys do want a tiny bit more in the inverted mode.  Manuever speed is what's critical, not lap times.  Equal lap times are what is used to get "in the ballpark".  Shim the tank once you're there to get the run right.

Bill <><

[Martin Quartim]

I am not sure if it is going lean or rich. It feels it goes rich. Because it doesnt peak before it slows down.

I will work some more on the weekend and let you all know the results.

Having to develop all these skills is what hook me into F2B. I  like a challange!


Martin

[tom hampshire]

Martin - I'd suggest that you run the tank shimming process out to the end of experimentation.  If that doesn't cure it, then you have the classic Fox 35 rich break on outside turns.  The fuel in the crankcase contains liquid oil which never vaporizes.  If too much of this mix accumulates in the bypass of the engine, acceleration away from the bypass, in a down turn, throws the heavier liquid oil into the bypass, it is swept into the chamber and fires weakly, cooling the plug and making the engine stumble.  The cure is to reduce the cross section of the bypass about by half, either by partially plugging it with epoxy steel(JB weld) or with a carved wooden plug.  You want to get the mixture velocity up, and keep the liquid oil from accumulating in the bypass.  If you are not comfortable with doing a teardown/reassembly alone, ask around, there is some engine geezer in your area who will help if asked.  Tom Hampshire