Sounds like you may not be choking the engine well enough for starting. Do a search for gas engine starting proceedures. I've written that many times already. The rest is all in the pushrod lengths, trim settings and engine tuning.

Balance gear down is good. There will be a slight change in balance when the gear comes up but that's easy to deal with at flight speed. If the gas tank is on the cg then you may not have a change in cg at all.