I have recently purchaced and assembled a PC-9. I installed an OS 46 (inverted) and it runs sweet when the aircraft is upside down but as soon as I turn the aircraft right side up (the engine upside down) it stops. I thought it was the tank position so I lowered it but it is still not working at lower revs in the inverted position. Can anyone help me?

Are you starting and adjusting the engine in the inverted position? If not, try it, because if it will start and run OK on the ground inverted, it should fly OK. You might want to check the "engine trouble" thread where I discussed a starting technique that CL guys use for inverted engines. Hope this helps.
Glen

Thats the problem. It will not start in the inverted position. I thought it was tank position but lowering the tank has not resolved the situation.

With my OS 40LA (control line set-up), I found that it wanted to start very wet. In fact, I had to go out about 4 turns to get it to start. Also, I found that it runs much better with a Fox RC Long plug w/idle bar. I think, and this is only my theory, that the longer plug puts the element up above any fuel that would pool in the combustion chamber and flood it out. I don't know if this is right, but the long plug just seems to work better. My RC planes are have straight-up engines, so I can't say for sure if these techniques apply to RC, but I would think that, in general, they would.
Glen

I think Wearden's got it right. You're probably flooding the engine if you're running too rich, which might be the case if you are just breaking it in. I would recommend that you remove the plug and check to see if fuel has accumulated in the glow plug.

Also, it may be that you have the fuel lines mixed up. I know it sounds silly but you never know.

Fuel line are fine as it runs great at high and mid revs. It just won't idle in the inverted position.

I don't know what to suggest for the idle, as my inverted experience has been with CL inverted engines and they don't idle, but the idle bar in the long plug might help. The idle bar was developed for a reason, and that may be it.
Glen

Sounds to me like you've taken care of the tank height issue, which should be centered at carb inlet level. With that out of the way, here's my take on the situation.

With engine inverted, fuel is pooling or building up in your glow plug; not with engine upright. Fuel presence at the glow plug cools it. To confirm, try idling with glow driver on, should improve.

If so, reduce the fuel flow into the engine at idle with the low-speed metering adjustment. On an FX, that's in the carburetor shaft, and on an air-bleed carburetor it's on the carb body next to the throat. With a leaner mixture the plug should stay hot & ready to go at idle.

I have experienced 3 engines which needed a larger air bleed hole to avoid the problem I described. Two were Tower .40's, one was an OS .25 FP. One numbered drill size larger than the existing air bleed hole was what they required. I mention this just in case you have an air bleed carburetor.

Good luck,
Dave Olson

I agree that it sounds like you just too rich on the low end.

Also, no matter what you do, short of an on-board glow lighter that kicks in at low throttle, you will never get an inverted glow 2-stroke engine to idle as low as an upright one.

Try a hotter glow plug, maybe even a 4-stroke plug. Those plugs will stay hotter longer, reducing the ability of the fuel to put the plug out. Many years ago, I used the Fox Miracle plugs for some engines. It's a pretty hot plug.

An idle bar, as suggested above can't hurt either.

I don't have any problems starting or idling inverted engines & I have never used an-on-board glow starter. I believe that the most important things to get right are correct low-speed adjustment & a good glow plug. I always start my engines with an electric starter in the inverted position (rather than turning the plane on its back). I suspect that most idle problems are associated with overly rich mixtures.

Sounds like you've bought a Seagull PC-9?

Even lowering the supplied tank to the minimum position possible with the rod removed but without former surgery, the tank position remains higher than optimum relative to the carb for a 46 installed on the supplied mount.

There are a couple of specific circumstance caveats, but I'll deal first with the general and remove later to the specifc.

Have a realistic idle expectation. In an ideal inverted situ with the right plug, ideal tank height etc, you might be able to achieve around 2k idle, but with that tank height still high, you'll have to be idling higher. Use a tacho.

Use a good condition OS #8 or quality equivalent heat range plug, and use nitro. 10% is best. No more than 20% oil, preferably synthetic blend and 18% by volume. An A3 won't cut it period and an A5 will be too cold for low idle with an inverted engine without lots of nitro.

After setting the high speed needle, re-tune your engine's low end (idle mixture) accurately.

A couple of Seagull PC-9 ARF tank fitment induced idiosyncrasies.

If you fuel and leave the model sit for any period of time, the engine will start to flood. That is a function of that tank height. Solution: Don't refuel until just before you are ready to start. Long term solution is to replace and refit the fuel system which includes modification of the PC-9 so that the tank height is perfect in relation to carb height, or refit the engine as a sidewinder or upright.

Upon initial starts after a flooded situation or if the plug is oiled up, the engine will not idle well until it has cleared itself and/or the plug. Very noticable if you start upright and turn the model over to place it upon the ground, when it will quit.

Solution: For the first start of the day, turn the model over and start the engine upright. Remove the glow igniter and rev the engine up to burn of any residual oil and clear out any residual excess fuel. Starts thereafter should be able to be made from the inverted position without any problem unless you inadvertantly flood the engine. After you've started always burn off any residual oil shortly afterwards and you should find that your engine will idle reliably and at a reasonably low setting.

FTR, I've a PC-9 with an OS46 aboard. Tank is lowered insofar as the design will allow with removal of the rod, but without surgery. I'll get around to optimising it, but mine idles reliably so for now, I'm happy to simply follow the start upright for the first start of the day procedure and not refuel until I am ready to fly.

Try it and let us know how you get on.

Hi I too have a 46 OS running inverted in a Sig Rascal and no end of trouble on idle . tried most tricks but to no avail. Then a old time vet. in R/C suggested I use a OS F plug and bing O the engine as been running perfect ever since, no more dead stick landings idle is awesome. Hope it works for you it did for me