Re: engine stalls out at wot
You might not have noticed, the primer bulb has an arrow on it, which is supposed to point in the direction of fuel flow.
The bulb gets firm because the float valves shut when the carb bowls are full of gas. (I know, I'm stating the obvious.) While the motor's running, the bulb is just a fat place in the fuel line, you'll feel some pressure, but it won't be firm, there's gas flowing through it. At idle, fuel pressure might be as low as 1 or 2 PSI and I don't think it ever gets above 12 or 15 even at WOT. When the motor stops, the bowls might or might not be completely full, but they ought to be mostly full, with plenty of gas for the next start. So the bulb might not be as firm as when you started, but it'll be firm enough.
On the tank vent, it's a built-in tank, right? I don't think there should be any restriction in the vent hose -- air has to be able to enter as the engine draws gas out (otherwise the pump has to pull a vacuum, which it can't do), and exit during refueling. Ever have problems with backsplash when filling the tank?
You could isolate any fuel tank issues by borrowing or buying a portable tank to use for testing. Three-gallon plastic tank from wallymart would be sufficient.
If it is a fuel problem, it's either too much or not enough. Either the carb bowls are running dry, or else they're flooding. And it's probably both carbs, cause I believe that motor will run on 2 cylinders (poorly, but it'll run). If there's still gas in the carb bowls when it stops, then it must be flooded. Or else both carbs have some kind of trash in the bowls. If not, it's either a tank/hose/pump issue, or else the float valves are sticking shut.
You probably can't replicate the symptoms by running it on the muffs (don't rev it up without a load on the motor), but if you can manage to be back at the dock when the symptoms start, maybe you can do some troubleshooting on the water. Drain the carbs to see how much gas is there. Do a spark test right when it starts acting up. See if the spark plugs are wet or dry.
Have you called the tech that did your carbs about this problem? In my experience (as an amateur outboard mechanic), sometimes you rebuild carbs and get a puzzling or otherwise "less than stellar" result. You take 'em apart & put 'em back together again and then everything works. Sometimes you can see what the problem was, other times you just "get it right" the 2nd time without ever discovering what went wrong the first time. Wouldn't expect that from a pro, but it's bound to happen sometimes.
I said earlier that if the fuel pump diaphram gets punctured gas will leak out the pump housing, that's from personal experience. But, I know that faulty fuel pumps can leak gas down the pulse line into the manifold, flooding the motor. I don't see how that pump can leak down the manifold without leaking out the back of the housing, but I can't say for a fact that it won't. You don't have any other symptoms of faulty fuel pump, but the repair kit is only about $12 and it doesn't take long to do. After ruling everything else out, a pump rebuild wouldn't be a bad idea. You'll need some gasket remover and permatex #2.
Keep us posted.
