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TD/Medallion .049 fuel draw issues Empty TD/Medallion .049 fuel draw issues

Post  Droobie Wed Aug 30, 2023 10:02 am

Hi all. I Have a TD and Medallion .049, and my father a TD .051. His was new out of the box, and both of mind have been reconditioned with new top ends. They will run fine on the bench, but I can not get either of mine to start or run consistently on the plane, and I am including the .051 my dad has in this as he has had the same issues.

Most recently, I have my medallion mounted on a fresh baby ringmaster rebuild, with a brand new Perfect tank. I have the tank immediately behind the motor, and the fuel pickup is a close to dead-nuts on center of the motor as you can get without being a machinist, haha. I also have the needle valve assembly flipped so when the motor is mounted on its side with the cylinder outboard (talking CL here), the needle is up and the fuel pickup is down- again, same as I would on any larger motors I set up without issue.

Running it last night, first- it takes what I consider to be an obscene amount of priming/choking to get the motor to even try to start beyond just a single "pop" every flip. Once its so loaded with fuel that it bumps on every flip, after 5-6 flips it will fire off and then quickly die, as if it is lean. I was playing very close attention to the fuel line and seeing bubbles, so I started leaning the plane a bit and finally was able to get it to start and stay running, sorta/kinda. I learned recently that closing off one of the two vertical tank vents will help motors draw fuel, I tried that with no improvement/change. There was a mixture of tiny bubbles, likely from vibration- I don't have foam under the tank and know I need to address that, but the lager bubbles were definitely confusing. Even with the plane tilted to "simulate" the centrifugal force and keeping the pickup tube completely submerged, the engine speed would still wander as moved the plane and bubbles would appear, eventually killing the motor prematurely.

I know most of this sounds like issues with my tank. I am running Brodak 35% castor fuel which all my other Cox engines absolutely love, and again- these motors run fine on the bench. The TD is mounted on a scratch built plane with the tank inside the wing, essentially on the centerline (of the wing) but definitely below the centerline of the engine with a longer fuel line. Interestingly, this one runs/starts a bit better- which is kind of baffling to me?

I guess my primary questions are

(a) do these motors need the tank mounted differently (i.e. not on-center)? I have two remote-tank "bee" engines that also have similar issues with fuel draw, however they do start and run fine on the ground- just suffer once in the air.
(b) does anyone get good performance with regular suction tanks or is a bladder tank the only answer?
(c) do they just hate being mounted sideways?
(d) should I try flipping the NVAs over so the fuel draws in from the top? Is that a known issue?

We desperately want these motors to run great! Its so aggravating having them, building models around them, running them on the bench and then kneeling in the sun at the flying field for 10 mins to get them to start, only to launch and get a lap or two before they die. Just hoping some TD/Medallion gurus here can weigh in with some good experience and tips, many thanks!
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TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  aspeed Wed Aug 30, 2023 12:21 pm

Could be the plane's motor mount is somewhat weak and is shaking making the bubbles. I have had that happen. Maybe a cheek cowl will strengthen things up if it is the profile type. Prop imbalance could make it worse. Suction should work if the carb hole has not been drilled out. Check normal things like holes in the tank or lines. I cover all the tubing holes with my fingers and suck on the easiest one and plug it with my tongue to check. Should seal for over a minute. No fuel in the tank of course.
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TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  balogh Wed Aug 30, 2023 12:32 pm

Droobie, I can chime in only with my RC experience as I only fly RC. My 049 TeeDees never suffer from fuel starvation or foaming/bubbles in the fuel line, thanks to the unpressurized balloon tanks I use. These are made of party balloons and have only a filling and a fuel line through a stopper in the balloon neck I place the balloon tank in the front compartment to be roughly level with the engine carb, and as near to the firewall as possible.
Though it is indifferent whether the engine runs on a bench or in a plane, unwanted air ingress into the carb along the NV thread may cause symptoms that you described. Just to be on the safe side, you may want to pull a piece of silicon fuel line on the threaded end of the NV such that it also overhangs the threaded end of the carb, to prevent air seeping in along the threads..

Looking forward to hearing of the solution you find efficient at the end..
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TD/Medallion .049 fuel draw issues Empty JTM.

Post  JTMosel Wed Apr 24, 2024 4:41 pm

All, I've got an Olympic .15 that has a similar problem to what I'am reading about on these posts. It starts and runs strong after priming with my finger over the rear air intake. Then dies. It appears that it's not drawing fuel from the tank when the engine is running. Also I've got a similar problem w/two other older .049's. Need help as I don't want to put these on airplanes and have these problems show up. JTM...
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TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  aspeed Wed Apr 24, 2024 6:34 pm

If it is a reedy and it is functioning good enough to run off the prime, then quite often there is something stuck in the needle valve assembly, or the needle needs to be richened out a turn or so more to start. Tee Dees have some small pin holes that get plugged in the venturi. The Bees can sometimes be flushed out by pressurizing the tank, by holding a finger over one fill line and squeezing a fuel bulb or syringe though the other one for a second or two. Not sure of the Olympic, but it could be flushed to make sure it is not plugged too. You can check them all by blowing through with a piece of tubing over the the fuel nipple. The reedies will need the tank removed for that.
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TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  Ken Cook Wed Apr 24, 2024 7:18 pm

Hello Drew, I just saw this tonight and I can answer many of your questions accurately and save you a lot of frustration. I didn't recognize your screen name immediately so I went into my messages to confirm. I saw your dad a few weeks ago. We had a 1/2A day at our field in the northeast. It was quite windy but in the later portion of the day things settled down to a flyable day. I had a TD on a modified Miss Ashley plane that RSM used to offer. I extended the fuse and changed the tips essentially only using the wing. Your dad was very impressed with this plane and it was on suction.

        While I prefer bladders, the key to success is to disregard ANY commercially available tank as being good. It's a must to take them apart and configure them properly. This is 100% critical to a proper engine run and no issues. Yes, I bought hundreds of tanks and used them right out of the box. I also have had hundreds of problems in doing so and never thought about the tank. I don't care about shape, newness, cleanliness, installation. Perfect tanks are terrible and Brodak tanks which now owns the Perfect tank line is not without issues equally. The pickup tube HAS TO BE SOLDERED INSIDE THE TANK. It has to be the proper length and it has to be in the correct spot.

      Because of certain tank shapes, I will use a wedge for instance, the pickup is too far outboard to work properly. Not only does this lengthen the fuel tubing, it has to overcome centrifugal force even further to enter the engine and this is where you problem is. The solution: Use a thinner longer and not tall tank. A coffin style tank works best. You won't find this tank available and it must be made. If you use a Perfect tank such as a wedge. Cut a hole in the fuse behind the engine and insert the wedge from the inboard side of the plane to the outboard. ONLY ALLOW THE TANK TO STICK OUT OF THE OUTBOARD SIDE 1/2". You want the pickup to be inline with the fuel barb of your TD. You can adjust your fuel barb projection by flipping the needle valve body which once the venturi and needle is inserted this can change the projection off of the fuselage 3/16" inches. While I don't condone engine offset because I don't care to shim the engine off of the fuse. Doing so can also project the fuel barb away from the fuse slightly.

          Now while all this sounds confusing, it will inevitably correct your engine run and if your still having issues in achieving a good run I can work this out for you. Making the tank uniflow is also a big game changer even if you choose not to use it. I try to use it because it can somewhat assist the craziness that can happen when the fuel load burns off. What happens with a TD is that when the engine is initially started the tank is full. The weight of the fuel from atmospheric pressure is keeping the run rich that is until some burns off and the problems begin.  To compensate, the needle would have to be so rich to regulate the later portion of the run the plane probably wouldn't leave the ground.

To answer one of your questions, yes the engine would need to be shimmed off of the outboard doubler which would also assist the problem with keeping the fuel tank pickup inline with the TD's fuel barb. The ideal situation is to get the tank directly behind the engine such as if installed in a full bodied plane and none of these problems would occur regardless of tank. The problem happens when mounting on a profile.
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