I'm considering mounting an OS FX .61 inverted in a 1/5 Piper Cub J/3 to avoid cutting the fiberglass cowl up to badly. I'm trying for a decent authentic look.

I've seen inverted, in cowl mufflers but a couple of shops have tried to steer me back to a side mount with an in cowl muffer. They state engine run issues with inverted mounts.

Anyone have any good/bad experience with inverted 2 cycles? I'm trying for good looks, but don't want a touchy, unreliable powerplant either.

Thanks.

The oil gums up the glow plug when inverted. You'll probably need to use 'idle bar' plugs. But that's just a thought, not from expereince.

As for side mounting, it is prefered. As the head may stick out the side, as this will help to keep the engine cool, not to mention ease plug changes. Most 'pitts' styled mufflers require the engine to be side-mounted, to have the stacks exit underneath. Inverting the engine will cause the stacks to point out the other side, where the on-off sdwitch typically is..

If your engine is in proper tune it dose not care if its inverted. A few things to watch for.
Some guys like to choke their engines. Be carefull if you do any excess fuel will gather between
the piston and head.For the same reason be sure to burn all the extra fuel out of your engine before you leave the field. (you should do that anyway)and watch the amount of after run oil you use. Also remember your carb will now be lower than your tank. Lower the tank as much as possible and put a
loop in the line between the tank and carb. Making sure the top of the loop is higher than the top of
the fuel tank. This will prevent the siphone effect. If this is a new engine I would break it in right side
up. It will be easyer to get the correct settings without flooding it. As far as a muffler there are some made for
an inverted engine. If you cant find one look at the Top Flight muffler that fits their Mustang. I think it can be
made to work.The canister on it mounts to the firewall with only a silicon tube connecting it to the header.
Hope this helps, later daveo

Before storing the plane after flying... run the remaining fuel out of the engine. get the engine running full throttle and pull the fuel line. That prevents most of the accumulation of oil in the glow plug. (can also pull the plug....) Then put some after-run oil in and flip the prop a few times.

Not bad advice for upright or inverted... but more imortant for inverted mounted engines.

When the engine is running, and properly tuned... it doesn't care which way is up. Starting an inverted engine requires more care to avoid flooding.

That's about it. Mount it the way you want.

Thanks for all your thoughts. It was just enough to get my brain in gear, build a run jig I could mount the .61 in and play with orientation. I can offer my experience...for what it's worth. Oh, the engine was already well broken in. I flew it right side up in another plane for all last season.

Got the thing mount right side up tank set with feeds mid carb. Started it up, warmed it up and tuned it just slightly on the rich side. Made sure it responded nicely to hard throttle ups off idle and that it idled well.

I then shut it down, flipped it 90 degrees and ran it again. It ran just as well as right side up. Same kind of quick response from idle and it idled well.

Now for the test. Mounted the jig upside down and started it up again. It responded pretty much the same as the other two runs, with one minor exception. If it let it low idle for a half minute or so and then went to full throttle it would hesitate a bit. Twice it stalled. As long as I went easy on the throttle from idle it ran fine. I guessing there may be something to the plug fowling theory.

Anyway, not enough trouble for me to worry. The cowling is going to look great without a big gaping hole in the side of it. Thanks for all your comments.

I would lean out the low end a little. AND/OR use an O.S. type F plug. That should cure the problem. You know what will happen first time you blow an aproach and gas it to go around? It will die because that's Murphys law.
Please tinker a little more till it's right. later daveo

I've heard that the inverted engines tend to "load-up" the glow plugs. I have never mounted one that way, so I can't tell you first-hand. I have avoided this orientation due to difficulty attaching and removing the glow plug heater. Many planes call for the inverted engine, so I am looking for a good remote connector for the glow-plug heater. Any help out there?

dkmorgan, the question is, will you be able to duplicate the same tank elevation in relation to the venturi in the plane as you did on your test rig? I think this is the biggest problem people have with inverted installations. Depending on the profile of the forward fuse area, it's sometimes very difficult to mount the tank low enough in the fuel tank compartment to prevent siphoning.

redneck, Central Hobbies sells a remote "Headlock" or you can make your own pretty easily if you're a tinkerer.