Mercury 8hp

[Merc714]

Hey guys I got a 8hp Mercury 2 stroke 2 cylinder from the 80's. I was wondering if it was possible to buy a carb from a 15hp and put it on my 8hp if it would work?

 

[flyingscott]

No it will not the 15 hp is a completely different block. In the 80s till early 90s the 9.9/8/6 hp all used a common block after that the 9.9/15 used a common block and the 6/8 shared a block.

 

[galamb]

That's correct the 15 horse needs a 16 cube block to make the 15 horses - the 6, 8 and pre-94 9.9's used a 12.6 cube block - so you can only squeeze so many horses out of the smaller block.

You can put a "pre-94" 9.9 carb on it, but you also have to change the exhaust plate and tube - there are two parts needed to make more horses - breathing in (carb) and breathing out (exhaust plate/tube).

Plus the plates (from pre-94) are discontinued. So while the post-94 plates "fit" they use a different style of water tube. It will fit down at the lower unit end but has a flare in it that prevents it from passing through the existing hole in the exhaust housing. So you take a long installers drill (like the cable guy uses) and you enlarge the hole in the housing (about half way down the leg) and that will let the flare pass through. Your existing water tube is held in place with a screwed in clip over the flared end - the new tube just has a grommet on the end and presses into the new plate - so you can "re-use".

So new carb ($260 new), new exhaust plate/tube ($96 new), new water tube ($40 including the grommet), throw in the gaskets you will toast changing things (base gasket, exhaust gasket etc) - call it 20 more bucks - a couple hours of your time and viola, you have a 9.9 horse which will make less than 2 more mph at the top end compared to your 8 horse.