1976 70hp Johnson loses fuel prime

I own a 1976-70hp Johnson. The last time I ran it, I primed it with the squeeze bulb and it started and idled fine. I advanced to full power and it ran normally for between 1/8 to 1/4 mile and lost power and died. I re-primed fuel and motor started and ran fine, only to repeat the same scenario over and over. Each time I re-primed it, it started and ran only to die again. Is my problem in the tank, fuel line or fuel pump. I was on smooth water running new gas. Each time I had to re-prime, the squeeze bulb was soft.

Re: 1976 70hp Johnson loses fuel prime

Welcome to iboats.

I would start with the free stuff first, be sure your tank is vented and the vent is clear, there is a filter in the tank, make sure that is clear.

There should be a screen filter where the gas line goes into the engine check that, if none of that gets it it is probably the pump, the diaphram may have given up the ghost, if ti is the original 32 years is a pretty good service life.

Good luck and repost results.

Re: 1976 70hp Johnson loses fuel prime

did you try having someone pump the bulb, when it started to die, if not try it. if that cures the problem, you either have a clogged vent, or bad fuel pump.

Re: 1976 70hp Johnson loses fuel prime

And just so you know, primer bulbs do not stay hard after the engine starts. Remember, fuel is being sucked through it, not forced through it so pressure drops when the engine starts. Also if there was a restriction in the tank or pickup, the primer bulb tends to collapse. If that doesn't happen, then the problem is very likely a bad fuel pump or possibly and air leak in the fuel line or fittings.

Re: 1976 70hp Johnson loses fuel prime

Thanks fellows, for your replies. I did make sure the vent was open, and I was alone when problem occurred, so could not have someone squeeze the bulb while running. I will check the fuel line for air leaks, and try a different tank in case of a filter problem there. However, sure sounds like a fuel pump repair job is on the horizon. Hopefully this does not require any special tools, so I can do this job myself. The old motor is not worth a very large repair bill. If someone could tell me how difficult this repair is, I would appreciate it. Back in the 60's, I used to rebuild auto carburetors, so hopefully this would not be any more difficult than that. Thanks again for everyone's help.

Re: 1976 70hp Johnson loses fuel prime

Its Very Easy And Not Expensive,there Are Rebuild Kits Avail,or You Can Just Buy A New One.go To The Home Page Of Iboats And Look For Parts For Omc,then Your Engine,your Looking At 2 Screws,and A Couple Hose Clamps Or Zip Ties,the Fuel Pump Is The Triangular Piece Which Your Fuel Line Connects To.you Should See A Picture On Parts Site

Re: 1976 70hp Johnson loses fuel prime

I have a 81 rude, and i almost replaced my fuel pump, but it started acting better. I raised up my fuel tank a little, so that more of a syphon effect could happen. But it is really simply to replace the fuel pump, but rebuilding it gets complicated, there are a lot of small springs and such inside the pump.

It should be around $90 for a new pump.

Re: 1976 70hp Johnson loses fuel prime

Thanks again guys for all your help. It is cold as all get out here in my part of the world now, so when warmer weather prevails, I'll get this job underway.
I really like this site, and will check in regular as I've had lots of electrical problems with this old motor and could probably be a help to someone else on down the line. Thanks and Merry Christmas to everyone.