1976 Merc 20 hp

I recently bought this motor and getting t into shape. Have several very specific questions and would appreciate some body to keep n touch with me on this.I have rebuilt th carbureor which resulted in instant starting and erfect idle and acceleration, but there is still a slight surg at full throttle. New tank and Mercury fuel line and Mercury primer bulb. I removed 2 check valve diaphragms from the carb, and replaced with only the black one, still died after a couple minutes at full hrottle. Then put back in the transparent diaphragm on top of the black one, whch lengthened the run time but still has the surge, corrected by squeeze on primer bulb. I the raised the loat level to the upper range of spec., which also helped, but not completely. The new style float has no float drop adj., and is hollow plastic, AND has different height spec, so I used the new spec. I am tempted to put the old float beck in it, but I also strongly suspect a pump issue. Does anybody know the proper check diaphragm to use on this motor? serial #4410261. I am also having some difficulty with the rewind starter and some other electrical questions, but this fuel issue is most pressing because I do not want to run this motor too lean for any time at all. I would like to talk to a pro who has some time and real answers, no guesses, please. I can supply phoos if needed. You may email me directly at piratebob@webtv.net

 

If squeezing the bulb helps, then it is a fuel delivery problem. A friend had a similiar issue, it turned out to be the fuel line connector on the engine. It was worn enough to allow air to ruin the prime. I would check that and the rest of the fuel line inside the case to make sure there are no cracks or loose connections that would allow it to suck air.

 

Merc 20 hp 1976

Thanks, Ken. I'm with you on the fuel delivery. I had a brand new tank and a new line, bulb and fitting from West Marine, and the motor would not run for more than a minute at WOT. Returned the line and bulb to West and got Merc fuel line, bulb, which made a great improvement in run time, but there is still the slight surge after 5 or so minutes at WOT. (Later found out that this West Marine line kit had been recalled after it stranded an acquaintance in the ocean) The engine side (male) fitting looks OK, side pins on the baonet lock are not worn, and the female fitting on the line is a brand-new cast metal one. I used all steel screw-type hose clamps. Even ran the motor with the tank vent removed altogether, and unscrewed the cap entirely. Bowl float is new, but not the same style as old one. Still would like to know the final word on the check valve diaphragms because my local Merc dealer told me to use the black one only. BUT- the shiny transparent one AND the black one BOTH were in my carb. Dealer told me to use one, and only one, and he says use the black one. I did it his way and no luck, so I then put both in as it was when I took it apart. Improved some, but not all the way. Every job I did has improved the motor to some degree, but it is not 100% yet.