Runs lean when inverted - OS91 3DS

[thefrog]

I've been running my OS 91 3DS for the last 2 1/2 years no problem. About 4 weeks back it suddenly started running lean what seemed to be randomly. A little more testing showed it happened when the bird is inverted. I've replaced the tank seal, clunk and clunk line. All fuel lines were replaced about 2 months back. Still no joy. I've also tried a couple of types of clunk line and lengths but this was never a problem previously.

What seems odd is there has been a bit of fuel in the line between crank and check value, and also a little fuel in the line from check value to tank. So I'm thinking the check valve may have failed or fails intermittently. The thing is, there is still plenty of pressure in the tank when I land.

At the moment it seems to be better when the tank is full, then gets worse as the tank level drops.

Any ideas?

[thefrog]

I received the new check valve today and installed it this evening. The new one flows a lot better that the old one. The old one flows and stops, flows and stops. Hopefully this sorts it out. I'll post the results this weekend.

[Rob43]

I for one am interested to hear your report.

[chabs]

I'd recommend try running a bladder in the fuel tank. For the little bit extra maintenance required the performance benefits and consistency far outweigh the extra maintenance.

[thefrog]

It was the check valve. Swopped it out and problem solved.

[Rob43]

I think I am going to replace my check valve as well. Last time ouit, there was always some fuel in the vent line. Plenty of pressure to bleed off, but it normally never spit fuel out and now it's spitting some fuel out. Running quality is a bit inconsistent throughout the flight.

[thefrog]

Originally Posted by Rob43

I think I am going to replace my check valve as well. Last time ouit, there was always some fuel in the vent line. Plenty of pressure to bleed off, but it normally never spit fuel out and now it's spitting some fuel out. Running quality is a bit inconsistent throughout the flight.

Let us know how it goes.

[Rob43]

The new check valve didn't make a significant difference in performance, but did seem to stop fuel from spitting out like it did before, or the appearance of fuel in the pressure line.


I believe I am simply seeing tuning issues. Flying last evening, I did some more tuning, and was able to really smooth it out. I think my idle mix was too lean, and hover mix was too rich. Last flight was awesome!

I hope you figure yours out. I would think inverted issues would relate to in-tank tubing/connections, but you said you had already replaced all that.

[thefrog]

The inverted issue is solved but the tuning isn't right. It still runs very hot no matter how rich I make it. I'm going to tear down the carb and regulator again, maybe also replace all the hoses again too.

[Rob43]

Another thought might be a cooler plug. I am liking the Enya #4 in such a case.

[thefrog]

I replaced all the lines again, including the in-tank line and pressure line. I got 1 flight in and it seemed perfect... then a Tx range issue caused a dirt nap. So it will be a while before I get to test again.