Old johnson running hot and can't figure out why

Guys,
I've got a little '57 7.5johnson that's pumping plenty of water but seems to be running hot. After about a 150yd. wide open run water would sizzle on the spark plugs and the rest of the cylinder sides were too hot to touch also, but didn't make the water sizzle. It's hot here of course (high of 94degrees) and the water is not cool in the lakes either. I have taken the head off and exhaust cover off and cleaned the water jackets and blown compressed air through the cylinder head and it seemed fine, blowing plenty of air out. the impeller is not brand new but the blades are barely curved with it out of the water pump and nice and flexible. It pumps nicely out the exhaust. I don't really understand why it's not cooling better. The water pump housing is not pitted and looks good, as does the bottom plate. I've looked at the grommets on the main water tube and they look fine. I've tried to make sure the intake screen is open and it appears to be o.k., too.
Anybody have any ideas? Wayne, Steve, F-R, anybody else?
thanks,
JBJ

Re: Old johnson running hot and can't figure out why

Does that motor have water deflectors in the head?

Re: Old johnson running hot and can't figure out why

JB, I'm not at all sure if this applies or not, but some of those motors had a restrictor up inside the water tube that liked to get partially clogged with debris. Don't tell anybody, but I used to drill them out. Sh-h-h-h!

Re: Old johnson running hot and can't figure out why

I don't know what a water deflector looks like. I'm thinking it's some kind of molded pieces that slow the water flow down? It does have some little areas that narrow down the passages but I've cleaned them out where they aren't obstructing flow as far as I can tell and it really pushes a lot of water out of the exhaust port. I'll check that tube but am unsure how I'll find a drill bit long enough if there is a restrictor in it. Anyway, thanks for the suggestions, I'll look and see if I can find anything.
JBJ