1971 Merc 800 80hp wont stay running

[clueless75]

UPDATE: Turns out the fuel line must have been a big problem as I replaced that (and sanded some corroded ground points) and the motor starts in under 5 seconds of cranking and runs pretty well! Although it idles a little rough, it performs very well at a higher RPM. As I took it out today, I discovered that the fuel line from the gas tank to motor had a giant rip in it near the tank and resulted in gas spilling out and losing pressure (which may be why the motor wasn't running great in the first place)... fortunately my brother had some hockey tape on him and we wrapped up the line real good and it held pressure! This motor is quite the beast! we had four people in my 15 1/2 ft Sangstercraft and we clocked in at 50 km/h max speed with us all! Thanks for the help everyone and here is the link to a clip of the motor in action: https://www.dropbox.com/s/hqd88l2gxb4f6uh/20160206_143622.mp4?dl=0

 

[sutor623]

Glad you got her figured out. I hope you got a new diaphram because that one just looks played out!! If it hasn't failed yet, it sure will one day soon with three people aboard at 5500rpms!! Next time you do a carb job on an older motor, check the fuel from the tank for debris/phase separation, replace ALL old/brittle fuel lines (I just replace all fuel lines either way) all fuel line clamps, fuel filter, and possibly even fuel pump internals.

Cleaning something all the way downstream and leaving old/dirty components upstream is basically a waste of time. If I were you, now that you have new fuel lines, I would AT THE VERY LEAST drain the fuel out of the carbs and check for debris in the bowl and high speed jets. Also I'd change fuel pump diaphrams. All it takes is one little piece of fuel hose to get jammed in a high speed jet, and you will either have motor issues, or lean out a cylinder and say bye-bye.

Good luck!!