1979 70 hp 3 clyinder 2 carb with a jet

help my outboard is driving me crazy. it starts and idles not to smoothly but not really ruff as i head out onto the lake i move thorottle towards full thorottle and it planes out and runs for about 15 minutes. came home and rebulit the fuel pump, lines to carb, and replaced the needle and seat and cleaned the fuel filter and bowl. put my test barrel under the jet and ran motor pulled the fuel lines off to check for fuel and its pumping really good turned off motor to reattach fuel lines primed bulb and started it back up it ran for about 10 minutes then just shook back and forth then died tried to start back up no luck unless i pump the primer bulb ran it agian then it died again while i was shakeing my head i touched the spark plugs and noticed that the number 3 plug was hot and number 2 & 1 were luke warm at best so no i am wondering what the heck is going on i am thinking ( or maybe i shouldnt ) that the top 2 plugs arent firing. if anybody has any ideas i can try please send them my way the steel head are in the river and i gotta get out there thanks Dennis

Re: 1979 70 hp 3 clyinder 2 carb with a jet

dbecker1 said:

help my outboard is driving me crazy. it starts and idles not to smoothly but not really ruff as i head out onto the lake i move thorottle towards full thorottle and it planes out and runs for about 15 minutes. came home and rebulit the fuel pump, lines to carb, and replaced the needle and seat and cleaned the fuel filter and bowl. put my test barrel under the jet and ran motor pulled the fuel lines off to check for fuel and its pumping really good turned off motor to reattach fuel lines primed bulb and started it back up it ran for about 10 minutes then just shook back and forth then died tried to start back up no luck unless i pump the primer bulb ran it agian then it died again while i was shakeing my head i touched the spark plugs and noticed that the number 3 plug was hot and number 2 & 1 were luke warm at best so no i am wondering what the heck is going on i am thinking ( or maybe i shouldnt ) that the top 2 plugs arent firing. if anybody has any ideas i can try please send them my way the steel head are in the river and i gotta get out there thanks Dennis

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also noticed a black oily substance running down the side of the motor looks like its coming from underneath the carb area. did a compression test and i have 122 on number 1 115-116 on number 2 125-128 on number 3. and also after it ran great for 15 minutes i could have the motor full thorottle and my boat would barley move

Re: 1979 70 hp 3 clyinder 2 carb with a jet

dbecker....how did the plugs look when you took them out??? Clean? Wet with gas? Heavily fouled with deposits?

Re: 1979 70 hp 3 clyinder 2 carb with a jet

number 1 & 3 were wet but not overly oiled like number 2. you know i worked on motorcycles for a living before any of the manufactor brought out outboards and this thing is just rattleing my head i never new an 2 storke motor to give me such a headache earlier tonight i pulled the plugs to check spark and its good and blue all the way down to me its starting to lead me in the direction of reeds or crank seals ( outboards have those right ) well any light you can shed on this would be great cause i really dont want to fish from the bank again

Re: 1979 70 hp 3 clyinder 2 carb with a jet

The fuel pump is pulsed by the crankcase of a cyl, a pin-hole in the pump diaphragm will leak additional fuel into that cyl causing flooding.

Pull the fuel pump and check for fuel leaking. A pump rebuild kit is cheap enough.

Re: 1979 70 hp 3 clyinder 2 carb with a jet

ok i pulled the fuel pump assy off and the back side off the diaphram is soaking wet. right now it starts and runs but its running really rich the water in my tub is all gray and cloudy but it only runs for about 3-5 minutes then dies pump blub and it starts right back up again running rich and sputtering lots off blue smoke

Re: 1979 70 hp 3 clyinder 2 carb with a jet

Rebuild kit may be all you need.

The pump is failing to fill the carbs, they are simply running out of fuel, yet the leaking diaphragm is flooding that cyl.

Just for giggles, by-pass the fuel pump and use your hand on the primer as a fuel pump, I bet it runs just fine.

Do NOT install an electric fuel pump, unless it is only for testing, elec pumps are not marine rated and a leaky hose or flooding carb can make for an explosive condition in a hurry.

The fuel pump rebuild kit is cheap enough and provides all the fuel your motor requires.

Re: 1979 70 hp 3 clyinder 2 carb with a jet

ok well here is a update on my motor i went thru the carbs again put new gaskets and a diaphragm bolted it back together and you know what i stood there and saw a sticker on the front cover that covers the air box and it had a picture of the location for max timing spark. so i got to looking at it and my motor was way off so i took the thorottle cable off and adjusted the trigger plate to match the picture and what a difference it made it starts right up idles a little on the high side but it dosent run out of gas and die or shake all around.and it also starting to clean it self out lots of black oilly stuff coming out of the exhaust and around the spark plugs (i installed them loose so that stuff could seep out ) so after a half hour of continous running at a little above idle i shut it down and about 7:30 tonight i went out and primed the bulb and turned the key and it started right up and ran another 30minutes with no problems so i am headed to the river in the morning and will give a update would like to thank you guys for everything and iboats fourm ROCKS i will never go look anywhere else for help or just to read and learn the wonderful world of mercury outboards thank you Dennis

Re: 1979 70 hp 3 clyinder 2 carb with a jet

ok well i took the boat out sunday morning and well lets just say 2 silvers and a king. motor ran great all day long. headed out to the puget sound here in about an hour .

Re: 1979 70 hp 3 clyinder 2 carb with a jet

I sure miss living in the Lynnwood/Everett area!

Re: 1979 70 hp 3 clyinder 2 carb with a jet

hey charlie its working great so far no problems it loads up alittle when trolling but other then that it runs out fine so you used to live up here right on i been up here since 1988 moved from so california ( dont miss that place at all ) but a little more history on my 70 hp mercury i had a friend that bought a house on some land over in moses lake area and we found this outboard in an old shed laying on it side so i took it home and the number 2 clyinder was full of rat or mice nesting stuff the jet pump was the same way and the wires were rotten in half so it took me about a month of cleaning reading and rewiring the thing and believe it or not she fired up on the 3 rd try so its been running since then and for some reason its running better then i ever thought it would but if you ever come back up here let me know and we will run around the rivers with this old motor thanks charlie for all your help Dennis