Any of the single cylinder engines in that size range will have quite a bit of vibration in the lower rpm ranges. It can sometimes turn out to be quite a problem. You may want to consider a twin cylinder engine in a similar size to balance out the vibes. I'm a Brison driver all the way, but I think in this case a ZDZ twin would be the winner. Unless, of course, Brison has a twin in the same size range. They do have a very nice 6.4...