That donut gasket is part number 73 in Gary’s exploded view of the carb. It fits over the end of part #28 and interfaces with the bottom of the carb bowl and when the bowl is screwed on it compresses this donut some. When I bought my QD-13, somebody had taken the carb apart and put it back together without that part – same symptoms you are having. I’ve seen this problem on several OMC carbs on a different HP motors from the mid to late 1950s, and into the 1960s.
Dave

That cam ware is from the little bits of hard coil plastic when running with cracked coils. . . 😉

Update: IT’S ALIVE!!! 😀 I got it all put back together this afternoon, filled the test barrel and put the test wheel of it. Clamped it to the barrel, primed the fuel system and gave it a single tug. It fired up and ran in one pull. Time to pull the gearcase for a reseal. It’s a runner. I made a video and I’ll try to get it uploaded later. I’ll post a link once it up. Can’t wait to try it on the boat!
-Ben

Yessir! That’s a great feeling. This one should make for a bit of fun conversation at the boat launch.

Here’s a link to the video.

https://youtu.be/Rf00GWsQFbQ

I did a little more tuning after it warmed up a bit more and it is running pretty well now. Looking forward to getting this thing dialed in on the boat. Come on spring!! I do still have lots of winter projects though. 🙄
-Ben

I got the lower unit removal figured out. Need to remove bother rear sections of the exhaust housing from the powerhead down to unhook the shift rod from the linkage. It then needs to be unscrewed from the cast connector and the lower unit can be dropped.
-Ben