Bench ran a new os 91 fx for one tank,ran fine.Mounted inverted in extra 330 with slimline inverted wrap around muffler could not get it to run right.Had to lean it to 3 and 1/3 turns out.The break in setting is 4 to 5 turns,and it still dies when i pull the glow lighter,and floods when it dies every time.
Tried useing the stock muffler with the same results.The tank is as low as it will go.Even if i relocated it.It is at the height that the manual recomends.I put the tank on the ground once and it ran perfect,but i cant fly with the tank on the ground so...This is BS. I spent a lot of money on quality stuff so i could just fly without problems,but here i am.Am i doing something wrong?
I am about ready to sell this thing and spend more money for 26cc gasser.Will i still have problems with the gas engine?
Thanks

To me it sounds like you might actually be to rich, especially on the low end. I would try leaning the idle mixture a little, then adjust the high end again and see if its better. The fact that it dies when you pull the igniter could also mean that the plug is bad.

yes sir I think you are too rich as well....rightie tightie is lean, lefty looseie is rich....3 and 1/2 turns out seems a bit

No! Your running to rich.

Break the engine in before you try to run it inverted, with the stock muffler.

Pitt's mufflers are also notorious for not providing enough muffler pressure. If your tank is too high this might be a good thing.

Break-in setting should be around 2-1/2 turns. Once your broke in you need to address the LS needle, then you can deal with the pitt's

As per the OS instruction manual, the first starting should be done at 2-2 1/2 turns out. My .91 runs about 1 1/2 turns and is set a few clicks rich.
I broke mine in with a 13x8 and found it runs great with a 14x8 and 15x6. after the problems my friend and I had with a used .91 FX I was considering
not buyng one but I haven't had any problems with mine. And my friends used 91 problems were all due to a airleak in the needle valve. We both run
our engines on their side with jett in cowl mufflers. http://www.jettengineering.com we have both also used slimline mufflers and found that if you plug
one of the exhaust outlets like some people reccomend the engine does not perform well.

Another thing you might consider, if this is a early production 91, they had a few issues that need to be dealt with.

Needle valve, back plate.

Gunfighter,
The used engine on my friends plane had the original needle cast into backplate. I replaced that with a remote
needle for a 1.60FX (overkill) but works great. My engine had the new design but I like the ease of mounting
the 1.60 needle so I replaced mine with that needle also.

I bought mine from tower hobbies two weeks ago.It has the remote needle valve,and the booklet that came with it says 4 to 5 turns out for break in setting.So i was scared when i brought that needle down to 2 and 3 quarters,but it ran alot better and the motor actually got warm insted of staying room temp after one tank at full tthrottle.
So it seems like you guys are right.I got puddles of caster oil all over from it spittin.Just that manual is freakin me out with its 4 to 5 turns out.

If it quits after you remove the glow heat, but runs fine with it clipped on, try a hotter glow plug.

If the tank is high, fuel will drain into the carb, causing it to be rich. I think you answered your own question when you put the tank on the ground and the plane ran fine. The easiest fix is to put a pump on the engine, such as the Perry regulator. That will solve the tank from draining into the carb.

What the manuals are really trying to tell everyone is the probable needle position to get your brand new engine to start the first time. They want to insure the engine starts with a safely rich setting.

In the case of this engine, they've either been too safe or they simply screwed up and printed the advice from the previous version of the engine. In the last couple of years, I've worked up 3 or 4 OS91FXs. Every one of them runs with a needle setting way leaner than 4-5 turns.

You really set an engine by the way it responds to the needle, not some set number of turns printed in a manual. It's a fairly simple deal. Once it's running, richen the needle until you're sure the setting is rich. Then lean it out slowly. If you were rich, then it will pickup rpm as you lean it. It will speed up as you lean it until it passes max rpm and then start to sag as you continue to adjust the needle. You quickly richen back up to the max rpm, and then richen some more. How much more? It differs with different engines. You'll sort that out by test flying. In this case, where you're wanting to break in the engine, you'll want to run it around the max rpm setting for breakin. With the latest OS engines, they describe running it for some seconds at high rpm. You've found that now. They then say to richen it up a bit to let it run cooler, and then run that breakin rpm for some seconds again. Well, you've found the needle setting for that.

You can easily repeat the rich-lean-rich-lean settings done during the breakin by simply counting the needle clicks from one to the other. It also helps to bend the needle extension (for the wire extension) with a right angle at the end so you can easily see the setting by where that right angle points. If you're using the flex wire and collar, you can see where the setscrew in the collar points, or the setscrew in the needle body.

The only real value of "how many turns" is when you remove the needle to pull off the cowl. You need to know that when you put the cowl back on and replace the needle. You really don't need to know otherwise. And you really don't want to adjust your needle year round by "how many turns", as different temps and pressures and such blow that technique to bits..... and can do the same to your engine. OK, won't blow up your engine, but ain't no good fo' it.

You a bad ***** Rock.Thanks for the tutorial.It was very helpfull.

You got it right from the ROCK. Forget anything else that was said. Rich, lean. rich, lean etc. for at least 2 tanks. P.S. Don't mess with idle screw until engine is broken in. Give it time to get there.

I just got a .91fx recently too and the manual also said to open it 4 or 5 turns....open up the throttle all the....and then start it. And it worked like a dream to my surprise,but you had to keep the throttle wide open to supply enough air. It ran super rich(4-stoke mode as the manual called it). My manual also went into how and when to start leaning it etc. All that worked great too. The only thing that baffled me for awhile was how it wouldnt run at all at about 3 or 3 and a half turns out while playing with the throttle. But I realized it just wasnt getting enough air when I backed off the throttle like it did when the throttle was wide open to support that much fuel. Once I backed the needle down even more,it ran like a champ.

The 4-5 turns out method actually works great if you read the manual closely. In fact my new super tiger .91 tells you do pretty much the same thing now. So,just lean that baby out and you'll have a great engine. And if not......I'll give you $50 for it!!!!