TOPIC: Evinrude big twin carb woes

Hi all,

I recently picked up a 64 40 hp evinrude big twin. The carb on this thing is driving me nuts. The previous owner said the primer bulb would not get hard , so I figured needle and seat. Long story short after an oem carb kit it still won't seal.

After hours of pulling my hair out I figured out that problem was actually the seal between the main emulsion tube in the carb body and the boss in the bottom of the carb bowl. After examination I found that the floatbowl was badly warped. Not sure, but I'm guessing it has something to do with the extra soft rubber bowl gasket, and over tightening?

To fix this I chucked the carb body up in my 4 jaw Chuck in the lathe and faced it flat. It took .035" to clean up. I them machined the corresponding boss in the carb bowl to the same relative height to the sealing surface. Finally I cut my own bowl gasket out of some stuff 1/16" gasket material and assembled the carb. Success! It seals and you can now pump up the primer system.

In all the motors I have worked on I have never experienced this problem. It literally drove me nuts and took me a full day to figure out what was going on.

Has anyone else ever experienced this problem? I wonder if it is common with these carbs?

Scott

Pretty common to see warped plastic float bowls on newer models. Not so much on the older aluminum carbs.

Do you have the little round cork gasket that goes over the emulsion tube to seal that passage in the float bowl? It'd run really bad without it, because it's not supposed to be a metal-to-metal seal between the float bowl center and the carburetor body.

See P/N 30 on this diagram:
www.marineengine.com/parts/johnson-evinrude-parts.php?year=1964&hp=40&model=40402S-R&manufacturer=Evinrude§ion=Electric+Start+Carburetor+Group

Lots of 'em listed on eBay, some cheaper:

https://www. ebay. com/sch/6000/i.html?_from=R40&_nkw=%280307778%2C+307778%29&_sop=15

Just copy and reassemble the link. This site parses ebay links.

HTH.........ed

Nice that you have the tools to do all that. Also that you figured out the problem. The shade tree mechanic would have put a thicker gasket on there, re-adjusted the float and then gooped it with form-a-gasket.
Helpful information. thanks for sharing.