Tired Old Man

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To all the engine gurus out there, and I hope there are many, I need some serious advice with a runing problem I am having with an older style, front needle version of the OS BGX-1, 35 cc glow engine. I think it has a fuel draw problem, but I'm not certain and cannot figure out why it would.

The problem is that no matter how the needles are set the engine will start to run erratically in flight and quit. Sometimes it will lean out, sometimes it will act like it is getting rich and quit. The set up is as follows and I will try to be as complete as possible.

The plane is a Lanier Ultimate Pitts. The engine is side mounted using the radial mount that comes with the engine. Fuel line to the carb is large diameter. OS #8 glow plug.

The tank is a Dubro 24oz tank, center line of tank is on center with the carb fuel inlet nipple. The tank is mounted with a foam rubber wrapper. No fuel foaming has been noted. The tank is set up with a three line system. One line is for pressure from a Bisson Pitts muffler. One line is for fill only with a fuel dot. It has a clunk. One line (large diameter) is from the tank to the carb, also clunked. The supply line also has a large diameter brass tube from the tank. No air leaks have been noted after replacing the "O" rings.

The engine has had a little over 2 gallons of Powermaster 10% fuel through it since I obtained it. This fuel has an 18% oil content, some of it castor.
Because I picked up this engine used after not running for some time, I replaced all the carb and needle "O" rings with factory new. The engine has excellent compression. The engine is not cowled at this time, so cooling is not a problem.

Props used are Zinger 18-6 and 18-8. Preferably using the 18-6 for a ground RPM of 8500 to 8800. Field elevations used are from sea level to approximately 800 feet above sea level. Problem occurs in all weather/temperature conditions.

I've become extremely proficient at dead stick landing a 14 lb. biplane from any altitude and attitude, but I really would like to land once in a while with a running engine after a rewarding acrobatic flight.

If anyone has any ideas, would you please share them with me?
This one has just about got me on the down side of happy. Thanks to all.

Silversurfer

Bob Pastorello

My Feedback: (198)

Try this experiment. Plug ONE of the Bisson tubes with a wooden dowel, needles should then be rich. Set high end so it is JUST on the rich side of lean, with the tube plugged, then fly it. While you're doing that, see if it is at all possible that the pressure line from the muffler is getting pinched in flight. That could cause strange things. Also, a small air leak at the carb nipple from installation of the tube...anywhere that it's possible airflow would be moving lines in flight.
I'm betting, however, that you'll find the Bisson not providing enough pressure to the tank with both tubes open. JUst a guess.

Diablo-RCU

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I'm going to guess it's the Bisson Pitts muffler problem. Outlet tubes too big, lack of sufficient pressure to tank so engine goes lean in verticals. Try holding it nose high on the ground at full throttle. Does it go lean and sag after some time? If so, then it's too lean. So now you have to set the high end a lot richer.

If this turns out to be the problem, try closing off one of the outlet tubes on the muffler to get more tank pressure.

Tired Old Man

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Thanks guys. I've tried the nose high lean test, and that doesn't seem to be the problem. I can't seem to duplicate the problem on the ground. I've tried about as many low end/high end needle combinations on the ground as you can probably have, and it still quits in the air after a while.

It does seem that more often than not it will slowly lose rpm after a drop in throttle position, from any attitude. Especially after lowering rpm and then bringing it back up again.

I am going to try the blocked tube idea next. But I'm still open to any other thoughts on the subject.

Pat Roy,
aka silversurfer

captinjohn

If you have 2 clunk lines in fuel tank.....make sure the lines are not hanging up or getting tangled.....just an Idea!!!! C.J.

luv2flyrc

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Can't see your setup but, over heating will cause the type of problems that u describe. Make sure that u have adequate airflow over the fins and head and ample air exit area.

I experienced similar problems with a Moki 2.1 that ran beautifully in another airframe but, when installed in my Super Stinker ran poorly several minutes into a flite, I had tried to get away with minimum cooling air exits,

Mike

tkg

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Check for crankcas leaks. Both at the rear and at the front bearing

Tired Old Man

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Thanks folks.
The engine is not cowled or covered yet because of this problem, so don't think cooling is a problem.

I have in the last couple of weeks replaced all the "o" rings at the carb and needles. That was my first thought after looking at them.

Regarding fuel, I've used fuel from 3 different unopened cans of Powermaster 10% from 2 different retail sources.

I haven't checked the case gaskets yet. I'll try that next.

Silversurfer

captinjohn

Silver: Maybe your pressure line is pumping bubbles into fuel tank. Try a tank with a bladder in it or cline fuel regualtor system. People say they like the consistant peformance of engine no mater what position the plane is in whith the cline system. C.J.

Tired Old Man

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Thanks Capt.

Do you know which mail order shops that might handle the cline system, and perhaps where to obtain more info on the Cline? It sounds like something I will want to look into.

Silversurfer

captinjohn

Silver: I would just type in cline regulator in the search box and click search. I have used the search and it works good. I sometimes forget to use it enough. Captinjohn

DMcQuinn

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I have had good luck with the Cline system on a Moki 180

Tired Old Man

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Diablo and CaptJohn,

What would happen if you placed a check valve on the pressure line? Would the carb vent enough of the pressure to prevent blowing the tank, or not? Or might a check valve in the fuel supply line prevent back suction from the carb?

I'm thinking that the Bisson muffler might be providing enough pressure at higher RPM but permitting pressure backflow/loss from the tank at lower RPM.

The problem seems to happen most often after the transition from high to low power settings.

Thanks again for the help so far. All you folks have given me more points to consider.

Silversurfer

captinjohn

If you put a check valve in the line it may help.....but when you shut engine off the pressure left in tank may push fuel to carb and flood the engine. If a lot of pressure is there, a lot of fuel is going to keep flowing to engine after shutdown. Unless you have a vent line to open on n or before shutdown. Hope this helps. CJ

Diablo-RCU

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I wouldn't use a check valve. The carbs are designed for high tank pressure at full throttle and low tank pressure at idle. A check valve will not achieve those conditions. A free flowing, non- restrictive exhaust like the Bisson Pitts will also not achieve those conditions. Making the outlet pipe smaller on the muffler will achieve it.

Tapio

Sorry for commenting as I'm not an engine guru but you might try ST fuel with less oil content in it.

300sflyer

My Feedback: (5)

You could be quite right... I have a friend who has a Supertigre 3250. It would not run worth a darn on reg glow fuel. He switched it to fuel containing only about 10% oil, and it then ran like a dream!

Good luck!

Tired Old Man

My Feedback: (1)

Thanks again to all. Every comment received has value and is appreciated. I'm certain that when all is said and done, one or more of the ideas in this post will have solved the problem. I'll post a note on how things go tomorrow.

Silversurfer

Stick2000

Just in case you have not try it , change the glow plug. Even if
it checks good. Had a engine with similar problem and it turn-out
it was the plug. It checked good but was defective !

stick2000

Joe Grace

BEEN THERE DONE THAT. CHECK YOUR PRESSURE FITING ON YOUR PIPE TO SEE IF IT IS STOPED UP. IF IT IS NOT TAKE A DRILL AND DRILL IT OUT JUST A LITTLE BIGER. IT CAN'T HURT TO MAKE THE HOLE A LITTLE BIGER , THE MORE PIPE PRESSURE YOU LET GO TO YOUR TANK BETTER YOU ARE ANY WAY. I HAVE HAD TO DO THIS MY SELF.
ALSO CHECK TO SEE IF YOU HAVE YOUR FUEL TANK AS CLOSE TO THE FIREWALL AS YOU CAN WITH OUT PINCHING YOUR LINES. REALY SEEMS LIKE A PRESSURE PROBLEM TO ME . MOST OF THE TIME IF YOU ARE PULLING AIR IN YOUR SYTEM IT WILL SHOW AT ALL RPM'S. LET ME KNOW HOW IT WORKS.

JOE

captinjohn

Make sure the new o-rings you replaced are the correct ones and installed correctly. Just a possibility Good luck CJ

Tired Old Man

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Just to let everyone know, I still have not had a chance to test out all theses great ideas in the air. Situations came up causing cancellation of flight this weekend. I'm going to have to put off untill next Saturday.

I WILL post info on the final solution when it comes about. Thanks again to all.

Silversurfer

Barry Fogal

I have had several large glow engines on Bisson pitts style mufflers and had to plug one of the tubes. I haven't seen where you have tried this yet. I will plug one if I have to open the high speed needle more than four turns.

You could use a fuel pump as an alternate fix, but I like to keep things as simple as possible when I can.

Tired Old Man

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Okay, here's where I'm at now. After plugging one of the tubes on the Bisson muffler, I noticed that fuel was blowing by the needle valve up through the housing. Flew it anyway.

It quit again in flight. This time I couldn't make it back to the runway and tipped over onto the top of the plane in soft mud. Minor damage, now repaired.

Removed the needle valve and noted that the new "o" ring, as supplied by Tower/Great Planes as the one for this engine, was a little on the small side for a proper seal in the needle valve housing. Went to the local hardware store and obtained a #60 "O" ring. Really fits a little on the tight side, but runs OK for ground static run ups. No leaks.

I'm going to try again this weekend and see what happens. I've got a feeling that I'll end up removing the plug in the muffler.

Thanks again to all so far.

Silversurfer

bdtsr

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What plug are you using? Try an OS "F" plug. Many larger engines will "Cool Down" causing the plug to flame out. My big STs would not run on non-idle bar plugs, would run ok on idle bar plugs, but run great on the "F" plug. Worth a shot.