Interesting thread.
I have a second-hand Vector that came with an Evo 36. Had to rebuild the front end around the plastic R/C engine mount it had. Never did get it to run happy, either in 2-stroke or 4-stroke mode. I switched to a NIB Evo 36 and it was better, but still not good. Tried both the medium and small venturis with an OS .135 needle thru the throat. Tried a number of props, but there are always more of these to be tested....
The only other engine I could find that would drop into the plane was the OS 35AX. Still took some mods to the cowl because while the Evo plug is on a slant, the OS plug is not. Also, the muffler header was slightly larger. Both easy mods.
Initial tests suggest I need to open up the venturi some, as it is a bit short on pull going uphill into the wingover. It also needs more run time on it. But the engine is beautifully made, and I hope it develops into a capable power source for my Vector OPP.
So if you have both of these engines, try them both! Or, if you have an Evo 36 and have had good luck with it in the past (some seem to be naturally good runners. I just don't have one of those...) try that first. If that doesn't work out, then drop in the OS 35AX. And if you get one from Randy that has been dehorned and civilized, so much the better..
I should also note that on my particular airplane, which does not have a stock nose, I had to add tail weight for the Evo 36. When I swapped in the OS 35AX I had to add a bit more. The OS engine is a little over 1/2 oz. heavier than the Evo. I don't have a number in front of me, but I suspect the Brodak 40 is lighter than either one.
Be sure to let us know, because I may not have found a good combination before you get yours working. Hive mind, buddy....
Dave