'59 Merc Mk 75A vs Mk 78A, difference carbs only?

[joaklay]

Bore and stroke for each are the same but the '59 Mk78A has 10 more HP. I assume the only difference is carbs (to add 10 HP to my Mk 75A) but is there more to it than that?

 

[Clams Canino]

Re: '59 Merc Mk 75A vs Mk 78A, difference carbs only?

Correct. (Previous to '59 mark 75's were 60ci)<br /><br />The 1959's were both 66ci. You'll need to change the carbs for sure, but there is also a question of the size of the throat holes in the intakes, and even more important the carb-bolt spacing in the intakes.<br /><br />My "area of extreme specialty" kind of starts with the 1962 Merc 1000 because you don't need two of them to power a boat. (though I'm fluent on the '61 Merc 800 FGS as well) I just don't **see** enough "dockbusters" to have the running changes as rote.<br /><br />Larry R or Sam on "John's Old Mercury Q&A Board" would know this answer right off the top of thier heads as they are Dockbuster desciples to the core. <br /><br />-W

 

[Clams Canino]

Re: '59 Merc Mk 75A vs Mk 78A, difference carbs only?

To give you all a bit more history here.<br /><br />The "Tower of Power" story begins in 1957 with the 60ci/60hp Mark 75. In 1958 the 66ci Mark 78 came out at 70 hp and ran concurrent with the Mark 58. (also appearing was the 44ci 4 cylinder 45-50hp "Super Thunderbolt" powerhead that would survive into the mid-90's and can still be seen bolted to Party Barges the world over)<br /><br />In 1959 everything got an "A" designation and the 60ci block was dropped, so both were 66ci.<br /><br />In 1960 the 76ci Merc 800 came out and the Mark 78 became the Merc 700. In mid-1961 Mercury finally mated a gearshifing lower to the critters. (both the 700 and 800)<br /><br />Lastly, in 1962 the new 89ci Merc 1000 was born breaking the 100hp barrier, and scoring a big feature spot in Popular Mechanics and got "really noticed" by the world at large outside of the "performance boater" niche. <br /><br />Brunswick, which had signed the merger deal with Kiekhaefer in 1961, could not have been more pleased. The "mile long outboard plant" in Fondulac WI, was (quickly)paid for by the sales of the Tower of Power and the 44ci Super Thunderbolt.<br /><br />-W

 

[joaklay]

Re: '59 Merc Mk 75A vs Mk 78A, difference carbs only?

Thanks for the reply and history. My Mk 75A isn't perfect but the price was right so it's now one of my many project motors. It has perfect compression but I havent tryed to start it yet.<br /><br /> I also have a '59 Mk 58 that's almost perfect and that's the motor I plan to use on a small antique boat someday.<br /><br /> I'd buy a Merc 1000 too IF I ever find one cheap enough that's in good condition. One doesn't see them around often these days, at least not for sale.