Spray bar. Take out needlevalve and reverse flush. Using a syringe blow fuel in through the needlevalve side, get a healthy stream flowing. Then put finger over the input side and reverse flow again, to clear the tiny feed hole. Fuel should flood into engine back up through the venturi. Check tank feed line, make sure there are no pin holes. Pull off line, squeeze end and blow. There should be no sign of air leakage. Reconnect feed line to tank. Fill tank. See if it is possible to extract fuel through feed line. You're checking to see if the feed tube in tank has broken loose and clogged. Usually what you describe is a fuel feed issue. If the above doesn't work, check to see if the back plate bolts are still tight. Could be a problem with crankcase vacuum. Less likely. But it does happen. See if there are any visible cracks in crankcase. Coat crankcase with soapy water. Flip over engine. Any tiny bubbles? Most likely trouble shooting the needlevalve will solve this.

Thanks Dennis i will try these suggestions this weekend.I did put different engine on this tank and it runs fine

   You are not getting fuel, or getting air in the fuel line.

    Brett

A bit of sidebar. The Magician I flew at the Nats was spot on then developed a peculiar repeating issue. It would start easily fly two laps, then quit. We flushed the needlevavle as I described. Same problem. We were about to go at the tank. Dan Banjok said wait a minute, pulled out the spray bar and had a look. Then proceeded to run a very thin wire through the holes. A barely visible piece of dirt came out. He reassembled everything, problem solved. John D'Ottavio was looking on and said he had a similar problem at one time. Flushing didn't work, but when he pulled the needlevalve and cleared it with a thin wire a minute fleck of paint came out. The incident made me realize how simple our fuel system is, at least at the engine level, not considering the plumbing of the tank. It's a tube that has a tiny hole and a screw with a tapered point. If the tube is clear and the tapered point is true, line up the spray hole correctly, and that part of the fuel delivery should work.

    We learned that one the hard way, too. Use the little bottle brush that comes in the Sullivan Fuel System cleaning kit, or the little bottle brush-type dental gadget (from the drugstore) and clean everything including the filter. Flushing usually works but every once in a while it leaves something behind.

   The most insidious debris are tiny almost invisible fibers. They usually can't be flushed out and show no obvious issues just looking and squirting fuel through them but when you run, the fuel can run down the fiber and not atomize properly, and stuff like that. Most of them come from unnecessarily filtering the fuel from the can by decanting it through a coffee filter. This is worse than useless, good quality fuel has NOTHING in it to filter out, but the fibers (not intended to stand up to industrial solvents, and a few fibers in coffee don't matter) from the filter can get in the fuel. I have run a sump filter and an up line filter in the fuel can, the same filters for maybe 100 gallons, and in all that time I have seen only a few specks.

   If someone insists on filtering the fuel from can to can, for goodness sake use metal mesh filter media intended for the purpose. It won't accomplish anything but at least it won't shed fibers into the fuel can.

     Brett

Great note about coffee filters and the like. I know folks who usually filter that way. I thought about coffee filtering but never got around to it. Good thing. I'll mention this caution to friends. No doubt they'll be adamant when they rebuff the advice. 

   Certainly!  We still have people who think in-plane filters are a huge source of trouble, but slavishly insist on decanting the fuel through a paper filter, then complain that the fuel if *filthy* and that their fuel can filter clogs up with fuzzballs.

   I take my fuel straight out of the can it came in and run it through about a 15 micron filter when fueling and NOTHING gets stopped by it. If it's smaller than 15 microns it will go through the rest of the system with no problems.

    Brett