DA-50 engine question

[sjs]

Here's my problem;

The engine is mounted inverted in the plane. When I roll the plane inverted, the engine richens up. When I roll upright, the engine leans out and runs smooth. I tried adjusting the low end, but no change. This only does it on low and mid throttle. At high throttle, the engine runs fine. Any thoughts?

[Lowkey3D]

Did you remove and flip the carburetor on this engine?

[Karmann34]

	Quote: Originally Posted by sjs
	Here's my problem; The engine is mounted inverted in the plane. When I roll the plane inverted, the engine richens up. When I roll upright, the engine leans out and runs smooth. I tried adjusting the low end, but no change. This only does it on low and mid throttle. At high throttle, the engine runs fine. Any thoughts?

You got an air leak in the fuel line bro... been there.
Mine was right at the fuel nipple to the carby. I pricked it somehow between trial fitting and making room. Mine was opposite of yours though... so might be something else.
Try to sort out the fuel supply lines and see how it works.
Another possible thing is you may need to run a tube from the top of the carb (diaphram) back into dead air inside the fuse. Hope you get it figured out.
Later,
Greg

[Bryant330L]

Mine does the same thing so I am interested to hear any fixes. All of my fuel lines are new so I don't think I have an air leak.

[Karmann34]

Actually, all my fuel lines were new too! I got lucky and smelled gas when I knew I shouldn't be. Good thing because we all know what gas does to foam.

But, I was hoping for an easy fix for ya. I know it's frustrating.

[ericb]

What plane is it on? You might need a static line from the carb to the fuse. Check it out on post 6. This has helped a lot of people when their engine changes tune in different orientations.

http://www.flyinggiants.com/forums/f...s-gassers.html

[yakpilot]

Boy that's weird. Usually they run rich flying right-side up and then lean out and pick up rpm flying inverted. If you can't fix it with tuning you still have a few options. First I would remove the diaphram cover on the carb. It's the thin one witha small hole on one side of the round circle. You'll want to plug this hole. Solder will work best but can use JB weld or even epoxy. Just make sure you clean it real good with alcohol first no matter which method you choose. Next you'll want to obtain a pressure nipple and drill and tap a hole near the center of that circle and install the nipple. Make sure to grind off whatever sticks through the other side so won't interfere with the diaphram. Reinstall the cover and attach a length of fuel line to the nipple. Route the fuel line inside the fuselage where air won't hit it. Some people use an old film can or pill bottle and drill a hole in them to accept the vent line. I like to build a small balsa box about the size of a matchbox and route the tube there. You don't want it absolutely air tight, your'e just trying to protect it from dierecy blasts of air. By doing this the engine should run the same regardless of orientation.
If that doesn't cure it I've also installed a second a second pressure nipple in the opposite side of the reed bleed block. You then connect the two nipples with a tee and then back to the carbin the original postion. The reason for this is to alleviate any fuel puddleing which can occur in the reed block. By doing this my DA50 ran flawlessly by allowing you tune me to tune the carb perfectly. Normally when trying to tune out the mid-range burble on the 50 you have to go right to edge of being almost too lean. But without these mods you risk dead sticks at low throttle. Some engines run fine without the mods and some can't run right without them. I can't explain it. Some of it is the shape of the cowl and baffleing if any. Also keep an eye out for loose carb bolts but don't tighten them too much as it easy to distort the plastic parts or even crack them. Also the gaskets can push out alittle and cause an air leak.
I hope some of this helps and good luck.

PS you can also solder in a piece of brass tubing in place of threading in a nipple.

[yakpilot]

I forgot to mention that when I ran a tuned pipe on mine the high speed needle could be backed out several turns without making it four-stroke. I swithed to a carb from a DL and was able to make sure the high end could be richened to a safe level. Not saying that I want it to fourstroke in operation, but I like to start off a little rich and tune from there. Overall I was very happy with the way that carb ran through the whole powerband. They are still Walbros but the DL is jetted a little better.BTW the carb off the 50 or 55 will work great. I've used them both.

[sjs]

The carb was never rotated. The fuel lines are tight and not leaking. I would think that an air leak would cause the engine to run lean, not rich. This is in a QQ Yak. I wouldn't think that air flow would be an issue since the carb is behind the engine and not in the air stream. The engine is baffled and there is plenty of airflow through the carb and out the bottom of the cowl. I called DA and they said the same thing as YAKPILOT. They said they never heard of this condition happening. DA said that it isn't a carb issue, but an electrical one. They recommended that I remove the DA ignition connectors and to check the connections and equipment from the ignition battery to the ignition itself.

[yakpilot]

You might want to change those Power Pole connecters to deans while your'e in there. I've heard of those causing problems before.

[sjs]

I'm going to remove them and see what happens. Where should you have the low end needle set? Mine is at 1 1/4 turns.

[FlyinTiger]

Sounds like the classic atmospheric pressure problem on the carb. Different air pressure on the small hole on the carb plate when upright and inverted. Several fixes outlined here on FG. From plates over the hole to a nipple with a fuel line run into the fuselage...what you're looking for is a consistent air pressure, regardless of the aircraft attitude.
Good luck.

Here's a pic -> http://tech.flygsw.org/walbro_carbvent.htm

[sjs]

Here's the pic of the engine. Notice the orientation of the vent hole on the carb. The carb protrudes through the bulkhead but is inside the baffled cowl. If I move the vent hole facing the rear of the engine, should that help, or just solder on a brass tube and vent into the fuselage?

[JoeAirPort]

Just solder a brass tube and vent to the fuse. Also 1 1/4 on the low needle sounds right. That's where mine ran the best. On mine 1 1/8 was too lean and 1 1/4 was just about perfect if not a hair rich.