Stalling at idle

[BlueFightingCat]

J40ELCDE
G7100857

So I bought a boat and it came with a 1986 Johnson 40hp. It worked fine when I bought and when I tried it out several times in the drive. But now that it's on the water, as soon as I start it, it will run for a few seconds and stall. I have no problems starting it but it will not run at idle for more than a few seconds. I use the "hand throttle/fast idle" lever to start the engine and I never get a chance to put it down since it stalls before it even has a chance to warm up. When I manually open the carbs, the engine seems to run fine.

First I thought it was a leaking primer bulb that caused the issue, but I replaced that but it didn't help. Next I took off the air silencer so that I could see what's happening in the carbs.

When I manually open the carbs in order to keep the engine running I observed two things:

1. Top carb was spitting some fuel out from the front end
2. Lower carb was not really doing anything. I couldn't really see any sign of fuel anywhere.

First I thought that the top carb's reed valves are worn but when I had a look, all reed valves appear to be fine.
So now my theory is that the bottom carb is blocked up and is not providing any fuel.

Before all this happened I had checked the compressions and both cyclinders were around 110.

What do you think?

I plan to rebuild both carbs since they are out of the engine but any advice would be much appreciated.

[ChampioNman]

Stick with OEM rebuild kits, may be hard to find in Finland but there are still Euro dealers over there. Good luck.

[BlueFightingCat]

I rebuilt the carbs and now the motor runs great.

[Bassmeister]