74 mercury 7.5

hello all, i have a 74 mercury 75. i am thinking the fuel pump is bad. been sitting a few years and i could get it started, it would run for just a few seconds and quit. i have cleaned carburetor a couple of times and the same thing happens. pump bulb start runs a few seconds and quits. have changed to a different tank with fresh gas and same thing happens except now it won't even start. have not checked spark, but will shortly. i am thinking it is a fuel pump problem but the thing is, the part to repair are no longer available on crowley marine or marine engine repair. so does anyone know where i might find parts for fuel pump? thanks

Re: 74 mercury 7.5

You need to start by cleaning the carb or rebuilding it, then the spark should jump a 1/4" gap and be bright and clear. New gas is a must. The water pump should be checked or replaced. From what you have stated the carb is still not clean as it would start and run for a short time. If it would run then your spark is probley fine for now. If you pump up the primer bulb and it starts and still dies, pump the primer bulb while it is running and see if it stays running. If it stays running then your fuel pump needs to be rebuilt. If parts cannot be bought here on Iboats you can try serching oldmercs.com on your search engine or the sticky Top Secreat here .
Oldman570

Re: 74 mercury 7.5

this motor is actually my uncles. i went over his house and shot some fuel directly through the butter fly and it will start and run and bulb stays hard, but once the fuel i put in manually is gone, it dies. he took carb off and i brought it home. tore it down today and he used some sort of silicone that is not compatible with gas on carb bowl. gasket has a break in it. i have cleaned the carb and reassembling it, and used a little dab of proper silicone just where the gasket is split. when putting the air/idle adjustment back in, i noticed an o-ring pushed up on the spring. obviously this does not go there, just not sure where. can not see in any diagrams where it might go.

Re: 74 mercury 7.5

http://www.iboats.com/Fuel-Pump-Kit-Sierra/dm/view_id.174939

Gerry

Re: 74 mercury 7.5

after cleaning carb, he put it back on. could not get any fuel through the carb, so he squirted fuel through butterfly. started and ran good, carb even started working properly. he ran it for a few minutes at an idle and even in gear. he tried to give it more throttle and it bog down and died. will not start without manually putting fuel in through the butterfly. so i am going to order a fuel pump kit and see what happens, it is considerably cheaper than a rebuild kit.

Re: 74 mercury 7.5

Try to start it again and when it starts to die, keep pumping the bulb and see if it keeps running. If it does, you will know for sure that it is the fuel pump.

Gerry

Re: 74 mercury 7.5

i have told him to pump the bulb when it starts to die, and he said he has tried that and the bulb will be soft. he also said it helps but it still eventually dies. he just ordered a fuel pump kit, so we will try again in about a week. thanks

Re: 74 mercury 7.5

he put the fuel pump kit in and called me and said that the problems listed above still exists. i went over to his house and tried to adjust carb to no avail. i took carb off and examined it. as i was disassembling the carb i noticed something flopping around between the butterfly's. upon further inspection, i found out that the venturi had broken the side tabs off and was just floating around. i have no dought that this is causing all of his problems. my problem is, i do not know exactly which venturi this carb requires. all parts break downs i have found lists 2 different types. 1 has strait tabs on sides and is no longer available. the other shows a venturi with angled tabs on the side and is still available. does the one with angled tabs super cede the one with strait tabs? the only numbers i found on the carb are as listed.......bb2b3..... and the other number is 4910a1.......any help will be appreciated.