TOPIC:

Well boatboy the flat blank plate on exhaust tube assembly you may have been right??
motor certainly is quieter but seems doing my running checks with 27 deg C water my top cylinder is getting hot at 80 deg C and bottom at 60 deg C..
I have to look back but certain when I originally got this 56’ running last fall it was even temps on both cylinders with no exhaust tube assembly plate..
the shiny chrome on spark plug is brown from heat on top cylinder and bottom one looks new still.
Not certain but may have lost this battle and a bit worried if I run it I’ll nuke top cylinder??

Thx Ray I’m going for it I think Evinrude wouldn’t have come out with different part super-ceding the old one part without thought. Again I’m over thinking things.. I’ll run probably have to tune a bit? And kept a close eye on water/motor temp..

The recessed cavities are probably both weight and cost savings and probably to make it easier to produce a good solid casting. The more consistent the wall thickness the more likely you will get good even solidification of the casting.

I asked the question on another forum Boatboy, this was what I got.

“376330 was officially superseded by 376786. No problem.”

thought I’d pass it on you have first version manual I bet and I have 2nd edition.. so guessing some 56’ Larks and older would have this tube, and later 56’ and up just have blank? Just guessing here, definitely more curious than ever, wish I had a couple laying around.

So it sounds like this exhaust loading tube assembly acts like a muffler so I learned something logical haha
just have to determine why Evinrude/Johnson changed to no tubes on plate to see if it’s safe to run blank, I assume yes as part number on my manual is the blank.. but assuming never seems to work out

John 
ya picture does show tubes and you can see imprint on flat plate 376786.
I’ll search for that part number you sent , but don’t see on eBay or marine engine.com “unavailable” so other than diagram in parts book it’s obsolete. 
thank you for part number wonder why my book is different number? Later versions on manual 

In your diagram part #107 clearly shows the plate with two tubes attached to the bottom of the plate. The OMC part number for the plate with tubes #107 is 376330. I haven't taken my 1956 apart to look but the 1955 Big Twin also has the same plate as the 1956 motors.

Ray that cavity is common to both water intake screen and exhaust out in photo. The water intake screen is common to the whole inside of leg. Exhaust water comes out of engine to the back narrow cavity to taddle tail but whatever exhaust water doesn’t leave taddle tail it goes through that circle hole under exhaust loading plate which is common with intake and engine exhaust I believe. (Pic might explain?)
willout plate the exhaust water essentially could be forced upwards past that plate to exhaust of motor?? 
again I’m reaching at straws here and not 100% sure on function. 
I seen plate was missing when I regasketed powerhead. 

Ray here are a couple pics I took a year ago tried marking up for a look maybe this helps? I’m certainly concerned now wether plate should have tubes or if it’s fine without. I ran motor pretty hard fall/winter and didn’t have any issues without plate, but I’m getting a heck of a lot of blow by oil collect from what I think is from exhaust hanging around base of motor at back where baffle plate was damaged and exhaust tube assembly plate goes. That’s with new powerhead seals and no leaks on engine.
my assumption and only that as I’m a rookie that baffle plate was damaged because of not having this plate… exhaust water/combustion can go anywhere with out plate I think?

So where does that cavity that the plate will cover go?