It sounds like your fuel set up is OK. Make sure the fill line (if you have 3 lines) is airtight when closed. I had a problem with my FG-20 with the fuel line not being airtight and the resultant negative pressure in the tank was too much for the carby pump to overcome. I don't think it is worthwhile trying to pressurise the tank because this will only mask whatever the problem is.

Remove any inline fuel filters between the fuel tank and the carby to minimise resistance possible introduction of bubbles. You might also try running the engine with the plane upside down to see if this makes any difference to fuel delivery.

The other thing to try is to replace the spark plug. You might only get an hour or two running with the first spark plug due to the varied running conditions with initial tuning. You can use a cheaper after-market plug rather than the expensive Saito brand.

I have the Saito FG-14 and FG-20 which are running well. When I have had problems it has been because the spark plug is nearly worn out or my fueling setup has had a problem. Sometimes it is a simple thing like the clunk tube falling off, the fuel bottle stopper not being tight enough, or a small split in one of the lines. Always keep the fuel/vent/fill lines with these engines as short and simple as possible. </p>