Ok, I can get my engines to work OK. but the fuel pumps I have seem to be sensitive to engine vibration which tends to cause the fuel to vaporize inside the pump and it looks like air bubbles going to the engine. So I isolate the fuel pump from the vibration as much as I can. I eventually went with a small box like structure and padded it to help minimize the vibration problems. Then you want to keep the fuel line from the pump to the carb quite short. The longer the fuel line the more problems you have trying to adjust the engine.

I would suggest for testing, is letting the pump hang loose and not touch the airframe on the ground, Then run the engine and see if that helps or not. if it does work for you, then you need to figure out how to mount the fuel pump to isolate it from the engine vibrations.

I do have a bit of a problem where the engine tends to run rich through the mid range and has a tendency to lag before it catches and peaks out on power. So sometimes the takeoffs tend to be interesting and longer on the rollout. But when the engine catches and peaks out, it stays like that in the air really well.

Getting the actual air bubbles out is a pain, so I have to move the plane around so that the pump has different angles to it to work out the bubbles before I fly it. Usually that first engine run of the day is the tricky part getting the bubbles out. but after that, once the bubbles are cleared out, it runs well.

You can see in this pic where the pump is mounted close to the engine so that the fuel line is short in between the fuel pump and carb. I removed the rubber bands later and went with a loose fitting velcro strap instead, so that the velcro on the pump back was isolating the vibrations. That worked pretty well. These bubbles appear to be actually gasoline vapor and not air bubbles. The gasoline is vaporizing inside the fuel pump and in the fuel line between the pump and the carb.


Here is a you tube video of me flying the plane too
[youtube]http://www.youtube.com/watch?v=D8ITI2qMJTI[/youtube]

In this video you can see what happens if I mount the fuel pump so that it picks up the engine vibrations. I was trying the special fuel pump bracket that lets you mount the pump to the back of the engine. But just letting the fuel pump dangle loose behind the engine had the fuel pump working really well then.So I feel that the pump is engine vibration sensitive.
[youtube]http://www.youtube.com/watch?v=cyfg3tsg0qE[/youtube]