1973 6hp johnson fuel pressure issue

I have a old 6hp model 6R-73S outboard. The motor ran great until last year and now behaves rather strangely. The fuel tank is plastic and in good shape, it has a new fuel hose and bulb and there are no fuel leaks externally on the motor.
Basically I squeeze the bulb pull the choke and motor starts and runs great , release the choke and go my merry way. But after about 3 or 4 minutes motor starts to die like no fuel. I finally determined that I have lost pressure on the bulb. As long as I pump bulb every couple of minutes motor runs great with no issues.

I was told by a fried to check some sort of diaphragm in the carb??? any thoughts as to what is going on ? it seems to me that for some reason the pressure is bleeding off somewhere.

thanks for any thoughts or assistance on where to look for this.

Re: 1973 6hp johnson fuel pressure issue

Well, the bulb loses pressure while it runs, all that does is fill the carb for starting, fuel pump supplies the gas. The fuel tank should have a vent on the cap, if it's not cracked while running it will eventually starve for fuel so check it. A weak pump will do exactly what you are describing so long as the correct venting is in place. If it starts, idles and runs wide open without issue then the carb is probably ok. Before doing anything check to make sure you have spark when it dies, it may not be a fuel issue at all.