TOPIC: mark 75 carb swap advice

Hey All,

I'm slowly getting the Mark 75 back in good order. I need your advice / guidance if a carb swap i'm considering is a good idea.

What i have is a 57 or 58 mark 75 that has the adjustable main needles. After running it all last season and having so many problems, constantly tuning the needles became somewhat of a pain.

I happen to have a spare set of fixed jet carbs of a 1960 merc 600DR that look like they would bolt right on. Im thinking that having the fixed mains would save me some headaches, but i also realize i will lose some tune-ability.

Anyone have any insight into this, or has anyone ever done it? Worst case is i can always put my original carbs back on if the fixed jets dont work well.

Scott

Scott,
I can't think of any reason why you couldn't successfully use the 600DR carburetors.
Compare the throttle links of course, but I believe they are the same since they are both 60ci DR models.
In respects to fine tuning, you will still have adjustable idle jets, and that is all you should need - unless you are boating at over 2500 feet above sea level. Then you would have to track down some fatter fixed main jets. No big deal.
If you can get a reply from Jim S, he is the 'go to guy' on the DRs.
doc

Agreed. Book calls for .057 jets up to 2500ft elevation.

Hey guys,

I have an update on the carb swap. the Carbs off the 600dr, will in fact bolt right on, however the profile of the carb body itself prohibits the full operation of the distributor linkages.

Basically the levers on the distributor that operate the linkage on the top of the top carb hits the body of the carb on its swing around. This could be solved by swapping to the distributor linkage from the 600, but at this point i think i am going to run my old carbs, and just re-pack the main needles.

Scott

here is a picture of what i mean

Hang tough on that decision motoscott909,...I don't think you have original 600DR carburetors there.
They look more like 700DR carburetors.
I'll try and dig out the real deal tomorrow, and confirm my suspicions.
If I am correct,...I'll peddle you a set of the right ones CHEAP.
More when I return.
doc

I found the set of 600DR carburetors.
See attached pictures.
doc F

Sorry i've been away from this thread for a few days. This darn cold has really been kicking my butt.

Thanks Doc for the offer, but im wondering if the linkage on the distributor will still hit the bodies of those carbs, where the lowspeed adjustment is?

I can definitely see a difference in the distributor linkage between 600DR parts motor i have and the Mark 75. The distributor on the 600 has a slight upward bend to clear the side of the carb bodies, where the mark 75 is straight.

Hopefully this makes sense? next time i am out in the barn i will snap a couple pictures.