1965 evinrude 40 hp big twin. high speed question

[freddybell79]

ok, so ive been having problems with my 1965 40 hp evinrude big twin. problem was it wouldn't go full throttle without bogging down. good spark,good compression, so I figured it was fuel related. did a carb rebuild. no it is running great.......... as long as the hood isn't on. with hood on and front door closed its like it is choking out. open the front door and it runs great again. anyone else had this problem?

 

[nwcove]

sure sounds like you have an exhaust leak under the cowl. ( thats assuming you are not trying to run it hard in a barrel )

 

[F_R]

What nwcove said. It is very common. As he said, it won't run in a barrel without smothering. But if you are experiencing it on a boat on the lake, the most common cause is the o-ring is missing from the top of the water pump housing.......Or the extension tube/orings if it is long shaft. Without all the seals, smoke travels up through the drive shaft tube and out the vent hole at the top, which in inside the cowling.

EDIT: Picture is for a V-4, but they have the same problem if the seal is left out.
http://s19.postimg.org/o9hhwgbxv/V_4...st_Housing.jpg

EDIT EDIT: Many people are quick to blame it on the fat seal ring around the outside of the housing. That is valid...But...That would smother it when at idle at dockside and smoke is bubbling up around the motor. However, at high speed the smoke is left in the wake far behind the boat.

 

[freddybell79]

that explains it then. haven't had it on the lake since working on it. running it in barrel. thanks guys