I am sure I remember reading (somewhere) that there are problems with mounting a 2 stroke inverted. The Rascal 40 I am considering will look a lot better with an inverted engine, but I would like to avoid the expense of a 4 stroke. What are the problems with running a 2 stroke inverted? Should I plan on getting a 4 stroke? This will be my second plane, so I am still real new to all this. Thanks...........

If the engine gets flooded, it is a worse problem with the engine inverted than upright or side mount (exhaust down). The fuel will pool in the head and you can damage the engine if you force the prop to rotate. Also, oil or residue will lay in the glow plug well when the plane is stored with the engine inverted. This can cause plug glow problems when starting for the first time. A sustained low idle can be harder to get with an inverted engine although thats been my personal experience because I know of quite a few inverted engines that idle very good. I run a Top Flight (red box) P-51B Mustang in Shangra-La decor with a inverted ST 61 engine and I don't spend much time on the runway before take-off although it will maintain idle for taxing back.

Glow plug becomes an oil sump and difficult to keep lit.

Consider an on-board glow heater, or mount it laying on it's side with a Pitts style muffler exiting the bottom.

Here's a sample of horizontal mounting using Pitts muffler.

Should'nt be a problem if you know how to tune an engine. Start with a good engine that has an idle adjustment screw. An OS 46 would be great. The low end will have to be a little leaner than normal but by using the OS or other higher quality engine it should not have any adverse affects. I run a YS-45 inverted with no problems whatsoever. Try the K&B HP plug also! Just remember to hand turn the engine over before you put a starter to it to make sure you don't have hydraulic lock!

Thanks guys. I had hoped to use an OS 46fx. If I can get by with the side mount, that sounds like the best option. Whole idea is to not have to cut a hole in the top or side of the cowl. If the 46 does not want to fit on it's side, I will just go inverted. If I can fit the 46 on it's side with the Pitts style, so much the better.
Thanks much...............

Make sure you lower the tank so the centre line is still very close to the centre of the carb barrel...not the needle in the case of rear mounted needle valves. You might also have to relearn how to prime the engine because now any fuel drawn through wants to just dribble out on the ground. Generally I'll just flip the model over, prime (not too wet!) then back on the wheels for the start.

I've installed an OS 46FX inverted in my H9 Aresti and have only had one problem with it. The scoop:

The tank just happened to be a tad too high. This makes the fuel very slowly run out the carb and drip on the ground. I consider this a good thing. Why? I don't have to prime. And the fuel will not flood the engine - it goes out the carb.

I ran a few tanks through it on the stand and broke it in according to the instructions. Then I adjusted the idle mixture. Now that it's in the plane and flown a dozen times or so, this engine has had about a 1/2 gallon through it. After a few flips with the glow disconnected, it almost ALWAYS starts on the first back-flip. If a back-flip doesn't start it, a forward flip does.

The one problem I had: I stored the plane sitting on it's wheels after flying. This allowed the oil to collect on the glow plug. Then it would not start. The solution? Very easy: Overfuel a bit so that some fuel runs into the muffler. Lean the plane a bit so the muffler is raised up. This will allow the extra fuel to find it's way into the cylinder and flush out the oil. Then follow the next procedure:

After fueling, to prevent hydro-lock, I always stand the plane on the left wing so the muffler is down then flip the prop a bit. This allows any extra fuel to run out into the muffler. Then I rotate the plane to it's tail. The fuel and oily gunk runs out the muffler. After this, the first easy back-flip usually starts the engine. I'm guessing that this primes the engine.

Yea, it may sound complicated. But it practice, it's no more difficult than priming an upright engine. Having the fuel tank a tad high makes starting so much easier than my other upright-engined planes (which would flood with a similar setup).

This is my easiest engine to start.

Want to insure easy starting, and reliable running ? Lay it on it's side ! And if the finned head protrudes just a little bit, it'll only improve cooling. I see that you live in Florida.

Yeh, what they said but i also have my own theory on this which so far has been very effective on this Mustang. A fair amount of Pilots leave their fuels tanks in the original position when inverting the 2 stroke.
* Doing this makes things worse. Turning the engine upside down now puts the carb alot lower than the tank therefore increasing a possible siphoning effect.
* If your going to invert your engine, lower your tank to help out.
I am running an OS 1.08 inverted in this P-51 with the fuel tank considerably lower to match and absolutely no problems.

Cyclic, can you be a little more specific about the "problems?"

I mounted my Aresti engine inverted - as designed for the plane - and mounted the tank just a very small amout too high. There is room to lower the tank. This caused a siphoning effect. I thought I did a fair job of describing why I thought this was a GOOD THING on an inverted engine.

The remaining text was addressing hydro-lock and fuel in the muffler.

The problem is that you are going to experience a tougher fuel draw when inverted, and your "setting" is going to change. You want to establish even running in all attitudes.

IDEALY, the centerline that runs horizontally through the center of your tank, should be located 1/4" to 3/8" below the spraybar in the engine.

IE > If your tank is 4" high, then the centerline is at 2" from the bottom. Take something like a black SHARPIE marker, and draw a line horizontally through the tank. Now mount the tank with that line 1/4" to 3/8" below the spraybar.

Let's see if I understand...

I'm not saying that the tank is above the spraybar - I'm saying that it's a bit higher than I've read or understood to be the "standard" - just enough to maintain a prime and/or sligh siphon.

In the configuration I set up, the fuel level is a bit high when the tank is full and the plane is level upright. When the tank is about 1/2 full, the level is low enough to stop siphoning. That puts the spraybar about centerline of the tank. So if I understand you, what you and I describe is pretty much the same thing except that the centerline of my tank may be closer to the spraybar.

I've read that the fuel draw tube (not tank centerline) should be a bit below the spraybar. This is the setup I see commonly. It appears to me that this would give you a richer run inverted, whereas the setup I describe will be more consistent.

I was trying to show that having a slight siphon in an inverted 2-stroke isn't such a bad thing because it maintains a prime and excess fuel just drips out the carb. I would think that if the tank centerline was just below the spraybar, this is what you would have on a full tank. But in an upright engine, a slight siphon like this would flood the engine if allowed to sit before starting. That's why I thought the idea was to have the fuel tank lower than you described.

So are we pretty much describing the same setup?

thanks