Mccullough Scott low profile 7.5hp.

[rude evin]

I just replaced both impellers in my 1963 McCullough Elgin Scott 7.5hp Low Profile outboard. This was the first time that I have had it on the canoe since I bought it. Prior to the impeller replacements I went through the lower unit, rebuilt the Tillotson carburetor, and replaced the recoil starter spring assembly, and have had quite a few hours into it. But when I took it out first the first time it over heated and now has no compilations in both cylinders. Can someone tell me what I might have done wrong and how to fix the problem?