I have a B-25 that has two Evolution .36 engines on it. I have been told that Evolution engines don't require break in but I decided to run a couple of tanks through them first any-way. One of them runs great and has good response and idle but the other is alot tighter to turn and takes a little longer to idle down, and doesn't take the gas like it's partner. It opens up and runs good at top end but I noticed that it has a knock when turned by hand at top dead center. It also seems to have more compression than the other. I think, or hope, that it just requires more of a "break in" but I decided to ask you out there. I have had engines that do require break-in that were tight like this one and had the same type of knock at the TDC that this one does. The no break in thing is something that is new to me. Do they do the break in at the factory or what? If so maybe they skipped this one. I definately won't fly this twin with them like this! Advice? By the way. I have ran 4 tanks through them as of now and intend in running more when I can go get some. Twins can suck up some fuel quick!