Peoples' experiences seem to contradict what Jaka said. In my travels, the general consensus is that you have to step up to the next size larger tubing, and if you're using anything but the stock muffler, you need to use a pump.

I'm running 5% Omega this year, down from YS 20/20 blend, and it still runs lean in the air, crackling and pinging.

I'm running the larger tubing from the tank to the carb, and I just got done ordering a Perry VP30 pump from Tower Hobbies.