OS.46AX runs too lean at 1/2 tank

[Fishbonez]

Ok I have a strange problem well I think its strange anyway. I have OS46Ax in Sig something extra. For some reason after flying about 5 minutes or so the engine starts to run lean. I tried readjusting the carb screw ran her up and everything seems normal take off and again at about 1/2 tank starts running lean again. Doesn't do it until I get to about 1/2 a tank. Before that everything is fine. Exhaust is tight, and fuel lines are snug. Any suggestions? I'm new to glow planes but I have a good grasp on the concept

 

[Freaky_1]

First check would be the pickup (aka clunker hose if it is such). First though, is the tank isolated with a little sponge foam. I have seen heavy foaming from airation (however it's spelled) cause the same situation.

Just a starting point.

Frank

 

[pgerts]

1/2 tank. Check the tube between the clunk and the brass tube in the tank.
It is not rare to see a tiny scar in the tube - or rather it is hard to find the leak that is there.
If you can see the fuel line to the carb - fill the tank to a quarter and run the (almost full speed) engine while lifting the nose of the plane and see if you find any tiny bubbles going into the carb.

 

[roversgonemad]

I am with pgerts, a rough spot on the pick up tube can poke a hole in the flex tube. When the tube is covered by fuel, no issues since it pulls fuel through the hole. As soon as the hole is exposed, it starts to suck air, in effect aerating your fuel, just like a cracked drinking straw. That's probably where I would start. The other option, and it depends on the age of the engine, could be an air leak at the base of the carb that manifests itself more fully as the engine gets hot. This is a case where I would start with Occam's razor, and ere to the simpler fix and that's the hole in the pick up tube.

 

[Fishbonez]

Thanks for all the help. I was afraid of that. I was thinking it might be that as well but wanted to rule out the obviouse. I bought this plane from a club member who also bought it already put together. So I will reseach how to remove the fuel tank and fuel line I will let you all know how it goes.

 

[Ron B]

when you put the fuel tank back in mount it with foam around it and a hold down that you can take out with ease.

 

[roversgonemad]

If the tank is a real bear to get out, you might check things like the carb gasket first, but the lean at half tank really does point to a pick-up tube issue. The OS engines are typically really reliable runners. I have an early 90s FP40 that just won't quit. I have run it into the ground a few times and minor tear down and flush and it's good to go again! No new gaskets o-rings or anything.

 

[Fishbonez]

Thanks everyone

Well after taking the advice of all the great people here on flitetest. I think the problem is fixed. I took her to my club field the other day and decided it was to windy to test fly her but did ground test the crud out of her and ran an entire tank through it while my flying partner tipped her sideways, up and down. She did not stall. Yesterday took her up and flew about 3/4 tank and she did not stall or begin to run lean.
So what was the problem. To be honest I am not sure. I could not fully access the tank so I could not fully check the klunk however I think it may have been stuck. Also I noticed the carb fuel line was not as tight as it should be and I believe it maybe wiggling loose so I heated it up a bit to ensure it stayed on the nipple. I also blew out my exhaust line. Finally I adjusted my carburetor screw on the bottom just a touch. I think after looking over all that I may have solved it with one of those or a combination of all. Again thanks to all the help

 

[Fishbonez]

Just a follow up I have flown the plane several times and no problems. I'm running a bit to rich which has ruined my "fuel mileage" lack of a better word. Still love this cool plane thanks again for the help