I have a u-can-do 60 with an inverted os 91 2 stroke. The tank is level with the carb. A perry pump is already installed. It runs fine on the high end, but it can't go to a low idle. It just dies. I thought the low end was to lean, but richening it up didn't help it. Also this probally means nothing but it has a three way fuel tubing connector between the carb and the tank. The third port on it has a tube with a fuel dot to make it easy to fill the tank. What do you think is wrong? What can be done to fix it?

What kind of rpm's are you trying to set the low range to?Have you tried to lean it out? It could be chocking on extra fuel while at a low rpm. Thats my sugestion, good luck.

What plug is in it, what fuel ( Nitro and oil % ) how old is the fuel? How is it being stored? Can air get to the fuel during storage?

If you flip the plane over, so the engine is upright, will it idle? If so you have to be close on your tune. Should only take slight adjustments to get it right.

Ken

Have you checked the carb o ring and needle valve for air leaks? A slight leak can let the engine run on top, but be bad enough that it can't draw fuel at idle. I'd also watch for bubbles coming through the fuel line which would indicate an air leak there.

Tank position is kinda irrelevant when using a Perry.
Things can get real rich though, simply just to much fuel bein' pump in.

Use an OS F plug (nothing else) and some decent 15% as a bench mark.
Set it up with the plane inverted (engine up-right) and adjust the needles in stages.
100% max power, 50% - 25% - 20%- 15% - 10% -  5% and your idle.
Find the point where it starts getting rich (it will because of the pump, normally seriously showing it's head in the mid range) and the cut out point.
You'll have to work on the low end needle not the high end.
 As soon as it starts richening, say 50%, screw in the low end some. It won't cure the problem but it'll help a little. Don't touch the high end needle.
Go down again, listen and adjust... keep on going a little at a time. Until you eventually get it down to a decent idle.
By this point you Low end needle could possibly be far further in than normal, your idle slightly higher than normal... but it's working.
Using a pump neans some comprimise.
You'll have to find the best one for you.

There are two operating systems used by Perry for their pumps and it is not sufficient to say it has a Perry pump. The two types are the ossilating pump and the other is the regulating pump.

The Ossilating pump depends entirely on it being mounted in specically on the engine back plate or the engine mount but not the firewall. It requires that it be mounted in the plane of the propellor rotation to be able to function. The regulating pump requires a pressure tap in the crankcase to operate the pump diaphram.

Now with the Ossilating pump there is the requirement to keep the pump wetted out during storage by keeping a loop of fuel line between the inlet and outlet with fuel in it during storage even just overnights. If you do not do this that tiny bouncing ball will sieze and stop bouncing and this can an will cause running problems.

You say you have the "fuel tank level with the carburator" What does that mean their could be three inchs differance there and OS is very specific about this, check their info on thank heights and do what ever you have to do to accomplish this and there will be no need for pumps.

Tank/spraybar height or relationship in any inverted situation is critical and very important to the success of the installation.

John

Hi!
Follow the KISS principle!
Get rid of the pump!
Get rid of the fuel valve!
Mount the engine on its side so that the carb sits right compared to the center of the tank!

OS 91FX two strokes had a design flaw that would produce symptoms similar to what you are descibing. Make sure you install the fix available from OS. IIRC it repositioned the remote needle valve.

Yes indeed. My 91FX (inverted on a Perry) had that needle valve assemble issues.<div>I cut the whole thing off and mounted a separate OS unit... similar to the one used on the 1.60FX.</div><div>I have to say, the .91 on the perry has issues... it's a trade off... but isn't near perfect.</div><div>The 1.60 worked just perfectly.</div><div>
I have my small FX mount in a small patern plane with the tank on the CG so I need the pump.
I'd agree the Jaka if your tank is in the normal place.
</div>

I got the engine used along with the plane, and it apears to have a non-stock needle valve on it. Not sure if its the "fix" that os put out or another needle entirely.
Also, with the perry pump, should I have the vent hooked up to the muffler? (I know stupid question) When I got it, the muffler had no nipple on it. I found it strange, and put my own on it. could this be forcing to much fuel into the engine?  

Does the pump have three fuel line nipples on it or just two and if it has just two how is it mounted?

John

John,


I'm a friend of waffleman,


It's mounted on the engines back plate. 2 lines. He don't
know how long the engine and pump have been sitting.
I like the idea of getting rid of the pump also. Maybe tomorrow
we will have better luck. Also mounting the engine sideways sounds
like a good idea also. Thanks to all for your help,

Bob

dignlivn


Hey waffleman, we'll try again tomorrow.

OK Bob that is the Ossillating pump and mounting to the back plate is the best place to do it if the inlet and outlet are to the sides in otherwords perpendicular to the crankshaft or in the plain of rotation.

The problem is, if this set up is used then its unlikely that the pump has been wetted out in storage and no doubt about it the ball will be stuck and this does cause many problems. It can be dissassembled and cleaned.

However this pump has no form of regulation like the regulating pump does and this makes using it on an inverted setup a bad idea in the first place. I agree with you the very first thing I would do is bypass the pump and try the engine agine.

John

Thanks John


We will try that.

Bob

Perry pumps have a diaphragm that does not last forever, and they dry out faster when left sitting. Ditch the pump, get a Cline regulator if you must.

I have posted this many times.

before I put any engine in any airplane I put it on a test stand and get the settings correct for the whole range of idle to full power. If the engine is then installed in the airplane and does not run properly it is not the engine, is it.

Ed S

Keep it simple stupid! +1

You hit it right on the head my friend. I second getting rid of the pump and fuel valve. Re-mount the engine on its side so that the carb sits right compared to the center of the tank. Remember folks, the more bells and whistles- and the more people complicate things, the more things can go wrong. And like Uncle Murphy's rules said, it usually does.



Correct. I was lucky enough to get a later model of the O.S. 91FX-ringed and mine didn't have the problems. I think I got mine 1 year or slightly less before Hobbico decided to discontinue the model. I guess the major flaw was the back plate design from what they told me.





Pete