50 hp mercury

[dunnym]

Hey everyone

so i have a 79 mercury 50 on my fishing boat. Took it out today for the first time this season. Fresh gas, new plugs. It will start and run, then seems to starv for fuel and dies. I can keep it running if i keep squeezing the primer bulb. How do these motors pull fuel from the tank? I cant seem to find any kind of fuel pump? I am using a old school 6 gallon steel gas tank. Anyone have any thoughts?

if i disconnect the fuel line from the carbs, should there be fuel flowing out of the line with the motor not running?

[delcecchi]

Have you checked that bowl thing on the side with the screen in it? Happened to me one time and I think that had something to do with it.

I messed around with some stuff and the problem went away. The bowl and screen had some crud in it.

[dunnym]

I havent done that yet. I think i will pull the carbs off tomorrow. I had the carbs went thru 2 years ago and always run non oxy fuel

[loadmaster]

Before I would do that, I would check for any type of vacuum leaks and check the fuel hose. Same thing happened to me but smaller engine and it turned out the primer bulb had gone bad. I think the check valve in the bulb would not hold pressure. As long as I pumped the bulb it would run fine

[RebelSS]

Loss of pressure in fuel delivery system from pinhole in bulb, gas line as mentioned, or in the diaphragm...which is my guess. Put your fingers under the carb diaphragm and pump the fuel bulb hard, if you get fuel on your hand, your diaphragm is leaking. Check your gas cap for proper sealing, too.

[BoxMN]

Do you have 6 gallon tank? That vintage motor needs the vent to OPEN I believe, our 82 does. It will do the same thing if that little silver screw cap on the metal tank rattles shut/tight. That is first thing I would check, next would get a BRAND NAME (meaning merc) new hose and bulb. Don't get cheap one from FF or Gander. It will cost more, but go a dealer and get the good one, but make sure it is merc brand and ideally with new metal fittings on the end.

If that doesn't do it, then you need more help than I can give but in the 33 years we have owned ours, the above has fixed every hiccup we ever had with similar symptoms. Good luck!

[dunnym]

Thanks, that gives me a few options to check out tomorrow

[gunner55]

I'm going to agree with Box since your bulb isn't holding pressure,check the vent 1st.Then I would look at the hose for a pin hole or maybe just a loose clamp on the bulb or end fittings.Do you have another gas line you can try?If it's the old metal 6 gal gas can check the fitting on the can also as they have a old style cork/paper gasket that dries up & crumbles also.

[sunniewally]

I had one hose suck air inside the tank. where it was connected to the tank valve. it had come lose.

[delcecchi]

Thanks, that gives me a few options to check out tomorrow

Don't forget the plastic filter? bowl on the side of the motor. You can watch it while running the motor to see if fuel is there or not. I still think it could be that screen in there.

[boatfixer]

Fuel pump diaphragms.