AD-12 w/Evinrude powerhead cooling issue

Working on a '58 7.5hp Johnson. Guy put a similar year 7.5 evinrude powerhead on after his failed (freeze plug w/model number is missing, so unknown year replacement powerhead..). He used the original head for cowl mounting and rigged up 3rd recoil mounting bracket/bolt. Runs fine, new impeller. Pumps plenty of water that is warm to the touch. Motor is overheating, as a little splash of water boils off the head while running. I shut it down quick.

Question- Is there any reason the evinrude powerhead wouldn't cool normally when attached to the johnson motor? I checked the water tube when apart and it was clear, and grommets are attached correctly. The old worn impeller was complete, so it shouldn't be a piece stuck in a powerhead port. Weird. Any help/insight greatly appreciated!

Re: AD-12 w/Evinrude powerhead cooling issue

Any ideas before I pull it all apart again? Thanks

Re: AD-12 w/Evinrude powerhead cooling issue

I plan on calling my parts guy Monday and see if the powerhead base gaskets are different numbers for '58 Johnson vs Evinrude '56-'60. I always assumed that all '55-'60 (at least) would use the same base gasket. Any thoughts??

Re: AD-12 w/Evinrude powerhead cooling issue

Guy brought in the original powerhead. They are different at the base gasket surface. Go figure! Must've been a change between years, or johnson and evinrude 7.5 powerheads were different at their bases..

Re: AD-12 w/Evinrude powerhead cooling issue

Yep, the earlier powerheads (with the recoil post at the 12:00) will not interchange with the later ones (with the recoil post at 11:00)...