TD/Medallion .049 fuel draw issues

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...

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.

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.