mid 70's 3 cyl Mercs

[horst86096]

I have the chance to pick up (free) a ski boat with a 3 cylinder 70's 65hp Merc, but the carbs are in pieces. I have seen only a bit of info so far, but what is the actual difference between the 65hp and the slightly later 70hp Mercs. If it's primarily in the carb setup, I would like to try and get some 70hp carbs, but if it gets much more involved than that I would just set it up as initially manufactured. Any help or advice would be greatly appreciated.

 

[FlyBoyMark]

Re: mid 70's 3 cyl Mercs

As I recall....I think the Mercs your are refering to have only two carbs...kinda a strange setup....These particular engines were peaked out @ 70 HP at the powerhead on some models and reved on the high side to get the 70 HP....generaly they were considered anemic....that last 5 HP won't do a hill of beans for you on that engine You might get 2-3 HP of that 5 to the prop..hole shots would remain the same and you might gain 1-2 MPH. Rework the carbs ya have and enjoy....

 

[horst86096]

Re: mid 70's 3 cyl Mercs

Flyboymark... you're right, can't make a silk purse out of a sows ear. I'll just rebuild the carbs and stick with an engine that doesn't have to be pushed to it's limits to develop hp. Would you know what year they stopped building that basic engine configuration (by that I mean engines that are virtually mechanically identical)? Thanks for the response!!

 

[FlyBoyMark]

Re: mid 70's 3 cyl Mercs

Sometime in the 80's when they prop rated Mercs, they were derated to 60 HP permanantly. They only had 49 cubic inches as I recall. I think they were made rite upto the 90's though. Then they were replaced by a 59 cu inch 3 cylinder that has THREE carbs, then the 49 cu inch was dropped. The new 59 cu inch block comes in three flavors; 40 hp, 50 hp and 60 hp. 40 and 50 are the same except for carbs and no reed stop on the 50. The 60 has some more mill work to the ports plus even bigger carbs. As of this date, these engines were discontinued this summer except for "stock" at distributors and Merc......(4 strokers replacing them...)<br /> You have roughly a modern day equivelent of a 60 HP. Decarboning this engine and making sure you have a good ignition system and well tuned carbs makes your particular "looper" run very well at higher RPMS. Sycronising the carbs was always a problem with your engine because of the unique setup. But once its set up rite, they ran very well when allowed to "spool" up to 5,500 rpm or more

 

[horst86096]

Re: mid 70's 3 cyl Mercs

Flyboymark, thanks again for the info!! I hope to pick up this merc on a Kennedy Barracuda with trailer this weekend. The previous owner is a bit of a mechanical freak. He builds these wild jetboats with a minimum of about 600 hp, so a 65 Merc is just to tame. I bety he's kept it in great shape though. Im giddy like a school kid at Christmas waiting to pick it up! (I'm kinda pathetic)<br />Take it easy!!<br />Horst