1971 merc 40 needs choke flipped on to go

Hello to everyone on this forum I am a newby here so please let me know if I need to repost somewhere else,this is a huge site,I can only hope I can find my post again

Well here is my delema.I've had mercs a long time and done all repairs myself over the last 35 years but my 1971 red stripe 40hp merc has me stumped.After 2 years I decided to put it in the pond and after having a heck of a time starting it.Brought it to the lake and it ran incredibly well! Infact it flew at 32mph on my alum starcraft falcon 14footer.I was delighted.So an hour later I decided to take it out again but I didnt pump the primer bulb I thought what the heck and sure enough it decelerated and stalled so I went out back there and pumped it till the primer bulb got hard and restated the outboard and went to take off and it wouldnt acclerate it would go only if I pressed the choke quickly and literaly coaxed it to sped up then it would die.I tried squeazing the bulb checking the tank vent even the connector I thought might be getting air.So I orderd a new fuel pump diaphram kit and tried that tonight and still no change I press the choke momentarilly and it tries to go faster,its weird like its spark advance related or that pack with 6 or so wires on it perhaps does anyone have any ideas?Because it doesnt really jerk like its intermittant or fireing on one cylinder but I DID try new spark plugs and no change whatsoever.This outboard looks very new for a 40 year old.

Thank you and help
Ed

Re: 1971 merc 40 needs choke flipped on to go

Sounds like it is time to clean and rebuild the carbs as by choking it richens the fuel mixture. The jets are partly pluged as you have rebuild the pump already. Ehtanol is bad on the older gas hoses and will cause them to flake off or swell up on the inside pluging the fuel flow and jets.

Oldman570

Re: 1971 merc 40 needs choke flipped on to go

I'll second that,replace those old hoses,clean the crud out of the tank and disassemble the carbs soak them in carb cleaner overnight and rebuild them.Your engine is running to lean.

Re: 1971 merc 40 needs choke flipped on to go

Ok I'll do that,the engine runing almost to well was a good indication that its running very lean,I'll empty the tank and pop the tops off the carbs and have a look at the floats etc.I will report back as soon as i can.

Thanks,Ed