I seem to have a related, but slightly different issue. I have my Evolution 26GT installed in a Seagull Yak55; it's been in that airframe for about 6 years now. A few weeks ago when the weather finally got better I serviced the fuel tank (new lines and filter) and took this plane out for it's first flight of the season. Right off the bat it took a bit longer to prime the engine than I remembered, but I finally got it primed. I fired it up and it ran for about 30 seconds and died. I tried restarting, but It would not even pop. I primed again and starter the engine up and again it ran for about 30 seconds and stopped. At this point I pulled the cowling off to see if I could determine what was going on. First thing I noticed was that the fuel line leading to the carb was completely dry. I primed the engine again, the fuel line was filled with fuel too, started the engine and again it ran for a very short time and died. Again the fuel line leading to the carb was empty. I thought there may be an issue with the fuel line so I disconnected it from the carb, leaned the plane forward (to make the clunk higher than the fuel outlet) and fuel began to flow at a pretty good rate. I believe this means that the fuel is not significantly obstructed. After years of service I thought maybe it was time to replace the pump diaphragm and the other membrane on the other side of the carb. I took the carb apart, cleaned it with carb cleaner, removed a fair amount of debris from the screen, put in new diaphragm, membrane and gaskets, put the whole thing back together. Same behavior: pain to prime and will only run for about 30 seconds.

in summary:

• Needles are set where the manual asks them to be set
• new plug
• Freshly charged ignition battery
• Good spark from the ignition system
• Fuel is fresh and mixed in with the proper amount of oil
• New gaskets, diaphragm and membrane
• Filter screen inside the carb is clean
• No blockage of fuel flow

• Engine is difficult to prime (I plug the little hole in the butterfly with my finger and I lift the plane's tail to ensure the tank fuel level is higher than the engine's fuel inlet
• Engine runs for about 30 seconds and stops

Any ideas on what else I should look for is greatly appreciated.

Thanks,
Jaime