Re: 1992 johnson 30 horse won't idle longer than 10 seconds
Your motor has the primer circuit for choke, right? This sounds like when you are choking you deliver fuel past the carb directly to barrel and at idle there's not enough fuel delivered from carb. The primer is fed also by the fuel pump, but this could also be that your fuel pump is blocked / shot in case the fuel lines were also in that condition. You could try to keep it idling by pumping fuel manually from the primer, then check if the fuel bowl in carb is empty after the engine stalls.
Then you should check that fuel is delivered to the carb when priming, and after that that the fuel is pumped to the carb when cranking the engine. Ground the spark plug wires out when testing or you might have a fire or an explosion.
If fuel enters into carb and supply remains steady, then the problem should lie in the idle orifice or behind it. Remove the orifice (Buy the special screw driver or you could be looking for a new carb body!) Use a compressed air can that are intended for cleaning electronics and blow some air into the idle passage, air should flow freely into the barrel of the carb and you should feel the air pressure if you put your finger on the holes in the barrel.
If fuel does not enter carb, open and check the pump and carb needle valve. First remove the fuel line from carb and ensure that the pump operates, then renew the needle valve.
Finally should you go after the low speed adjustment, my older 35hp outboard will also stall at idle every now and then if the idle is set too low and/or mixtures are off.
