They are lengthing the spring. It will put more preload on the popoff or the needle valve that lets gas into the metering side of the carb. Gokarters regularly change this setting and have special pressure guages that check the point that the valve releases. You can actually get springs of different strengths to set this valve.

In any event I will also try it tomorrow. My 150 four strokes/goes rich when inverted and I have changed everything. I have flown with the cowel off and it made no difference. The fuel tank is just above the carb in level flight and below it when inverted. I am now assuming that the pump works harder inverted and overcomes the popoff pressure some how.

I am beginning to think there is something else wrong with the engine but I sure don't know what. I even tried turning the ignition upside down.

CB