mid 70's 4hp design question

[lark2004]

Hi all,

I'm in the middle of rebuilding a 1974 4hp Evinrude, and I noticed something that I hadn't paid any attention too when I had my 1980 4hp Johnson apart.

The porting into the crankcase from the reeds is different between the top and the bottom. The top port is a lot bigger than the bottom.

Is this meant to be different or is it just a casting flaw?

 

[lark2004]

Re: mid 70's 4hp design question

^bump

 

[lark2004]

Re: mid 70's 4hp design question

anybody???????

or does no-one know the answer?

 

[Joe Reeves]

Re: mid 70's 4hp design question

If you're speaking of the cast opening in the crankcase that the leaf plate covers (between the crankcase and intake manifold), it would make no difference. The air vacuum created in that area would be identical due to the fact that the pistons and their throw are identical, as are the leaf plate valves.

 

[lark2004]

Re: mid 70's 4hp design question

Thanks Joe,

I figured that was the case, but wasn't 100% certain that it hadn't been done for a reason.