I just wanted to give a vote for the Saito on the OP's 4 * 40. I have a Saito 56 on my son's Sig Kadet. We started with a 12x6 and now use a 13x4W acp on it. The flatter prop helped cut down on the float. Now the 56 flys it great with good power but a 72 or 82 would be of more use later on for just a little more money. As for the cost of fuel for YS engines I use Powermaster 20/20 in Saitos , OS 91 and YS 1.10s the last I bought was 24.00.