Re: 1991 Johnson 200hp Air Silencer help needed...
Everyone is thinking the problem is in the carbs??? This will at least give me a starting point. If the gasket is swelling and covering the idle and intermediate jets would that cause the problem? The HS Jets were located inside the carb after I removed the bowl, if I remember correctly, correct me if I'm wrong.
A item that hasn't been mentioned, mostly due to the fact that if this condition existed, it would result in the fuel pump/VRO malfunctioning, but check it anyway. Find the pressure hose that leads from the fuel pump to the crankcase (block) and temporarily disconnect it. Now, pump the fuel primer bulb while observing that hose. If fuel flows out of it when the primer bulb has been pumped up hard, the pump diaphragm is faulty... rebuild or replace the pump.
It would be an excellent idea, in my opinion, to question the previous owner to see if (to his knowledge) those carburetors have been changed, jets changed, whatever. Having worked on those engines in a serious manner for over 30 some years, your explanation of the problem leads me right into the carburetor area. Unfortunately some boaters think they are somewhat wiser than the engineers that design these engines... and decide to improve them with complete carburetors that have wider throats, physically modify the carburetors, or simply install bigger jets.... all of which simply create problems.
The carburetor throat mention..... you would need to know the original specifications of the designed carburetor in order to compare. Some other member will need to forward that information.
Let us know the numbers imprinted on the jets.... High, Idle, and Intermediate jets.
The mention of the gasket swelling..... If that hard heavy duty gasket has swelled, although I assume it's possible but it's something I have never encountered.
However..... The design of that gasket is such that there is a cut out for each individual carburetor throat. If anyone has decided to make their own gasket and replaced that gasket with some other look alike gasket material..... and neglected to cut out the precise openings to allow air to enter the carburetor throats, that effectively creates a choking effect upon the carburetors. Unlikely this condition exists but it's a thought.
If you're close friends with anyone that has the identical engine, or are friendly with a dealership or other outboard repair shop mechanic who might have the identical engine in thier shop, ask if he will compare one of its carburetors with yours (casting numbers, throat diameter, jets, etc). I can think of no other reason for your problem UNLESS you have a electric fuel pump inline forcing fuel past the carburetor float needle valves.
