You can fit a 6 ounce on a Tanager. Using a setup similar to one you describe proved repeatable and controllable on a Tanger. Engine hung a tongue muffler. Run characteristics were very similar. I used a six ounce clunk plumbed for unifo. Every bit of 6 ounces was consumed. A stunt friendly run.


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4.9 second laps is too much speed (if not power), yes.  That, and dead rich means that the venturi is too big for that setup, no matter what the next guy over is flying.  I'm surprised it's not running away on you (well, more so than already).

My recipe for the 46LA (and 25LA) is to start with the right prop and fuel, then keep restricting the engine until it flies right.  You can either do this with a smaller venturi, or by piling on nylon mesh (find it in the wedding dress section at your local fabric store, or ask at your local florist).  Hold it on with a rubber band or O-ring.  The nice thing about mesh is that you can tune it at the field, by adding or subtracting layers.

If it runs away, there's not enough restriction.  If it "thins out" in maneuvers instead of staying authoritative, there's too much restriction (because you have to launch lean to get the power you need).  For either one, the motor may need a good cleaning, or even a rebuild.  If you just can't get there from here with that motor/prop combination, reduce overall available power with a bigger prop (go toward the APC 12.25x3.75) or increase overall available power with a smaller prop (go toward the APC 11x4).

Figure that whatever else you do, a heavier plane is going to use more fuel when it's working properly.  My Fancherized Twister, at 54 ounces and 5.2 second laps, uses 4 ounces of Powermaster GMA 10% fuel (with 22% oil, 50/50, and doctored with a bit of Coleman camp fuel).  My Walker Atlantis, at 64 ounces and 5.3-5.4 second laps, uses 6 ounces of the same fuel to do the same thing.  I have some 40-45 ounce trainer planes that use Tower 40's and APC 35's that only need 3 - 3.5 ounces of fuel for a complete pattern.

I do not think that you should just make one more venturi and try it -- if you're not going to tune things with mesh, then make three venturis in the 0.270 size range and see if going up or down in size helps.  Then make more as needed, either smaller or larger.  (Brett Buck has some recommendations on how many to make, and what sizes -- I looked at that, thought "ugh!" and kept to my bright purple nylon mesh).

   I'm having trouble seeing a 4.9 second lap on 63 foot line with an engine  "in full four stroke." That would be in the 8000 RPM range with that prop, maybe 9000 and it would be pulling much at that RPM and you are not near the best part of the power band for an engine like that. It was designed to pull at much higher revs. On a small model, with an LA.46, I would try some 11 -4 props, with narrow blades. Something you have to lean out a bit to get the speed you want/need to get to and also get it up on the power band a little more. I don't think a .270 or even a bit smaller on the venturi is out of the question either.
   Type at you later,
   Dan McEntee

That might not be a bad idea, have you seen the price of nitro lately? $78 gal.

How small can I go on the venturi .270"?

OS makes the small one  at 255   so you could start there, and open it up to 260 or 265  ,  whatever is needed

Thunder Tiger  Cyclone  11 x 4.5  would be  great for that setup

Randy

I've been using an LA 46(not worn out), a stock muffler, in a Brodak Original Smoothie.  A .250 venturi, an OS through the venturi needle valve, and a 10/5 Master Airscrew 3 blade prop.  It runs smoothly at 10,300 on the launch and does a nice 4-2 break in maneuvers.  Lap time on 60 ft. lines is about 5.2 seconds.  The tank is a bit too high so it goes a bit rich upside down and on outsides.  I need to fix that.

I may try a cut down 11/5 MA 3 blade to get a little more thrust up high.

You might take a look at the main bearing.  If it is engine is well worn in may be leaking some fuel out the front.  If you can see more than an occasional drop of fuel coming out that can be enough to leak out half an ounce or more of fuel in a flight.