1957 johnson 7.5

Goodday all
I have a 57 7.5 that will start willingly after being primed from the tank but will die immediately. If I continue to push the priming button repeatedly it will continue to run but if I stop it dies.
Any suggestions

thanks drastic

Re: 1957 johnson 7.5

sounds like the tank is not holding pressure. there are 2 types of tanks, black plastic button, and metal button, the tanks take different rebuild kits. they are available at laingsoutboards.com. before that make sure there are no air leaks in any of the hoses, this would cause it to loose pressure, also. the way the system works, is , you pump the button to get gas to the carb, for start. on start the engine pumps air into the tank, pressurizing it, and forcing gas to the motor. thus if leaking anywhere, the gas does not get there. also the float needle valve in the carb could be sticking, and the air pressure may not be enough to force it open, where the pumping does. are you totally confused yet.

Re: 1957 johnson 7.5

The sintered filter in the bottom of the carb could also be partially clogged, allowing enough gas to be crammed through with the primer but not under normal pressure. Take the filter out temporarilly and try it. If it runs then, you need a new filter.

Re: 1957 johnson 7.5

Thanks for the quick responses
I tried with two different tanks with the same effect
both tanks hold pressure
will try removing the filter when I get home tonight
thanks drastic

Re: 1957 johnson 7.5

If the engine has been running even a short time, you should here air escape when you open the fill cap. Does it do that?

Re: 1957 johnson 7.5

Yes I do have some pressure when I release the cap
I am waiting on anothe known good tank to arrive either this weekend or next

thanks
drastic