Mercury inline 6 90 to 115

[sfara002]

I plan on upgrading my 1979 90 inline 6 to a 115 block from 1984 that I have access to. I know there is tons of knowledge here about these old motors from reading. I think I have everything already I need to do the swap. My question is, could I use my carbs from the 90? If so would I have to change the size of main jets in the carb? If there is already a link to the subject please share. Thanks in advance.

 

[jimmbo]

Welcome to iboats
When you say Block, do you mean a complete engine? Or just the engine block, no reeds, no crank, rods, pistons?
Carbs are different(not just the jetting), so is part of the linkage that syncs the carbs to the ignition. Exhaust tuning is different. Other differences include: no chokes on the 84 carbs, uses an enrichment system.
Just for your info, the 78 90hp is crank rated, and the 84 115hp is prop rated. I replaced my 78 90hp with an 84 115hp in 1984 and the boat gained 10 - 11 mph.

 

[Faztbullet]

Need more information

 

[jimmbo]

Just for your info, the 78 90hp is crank rated

Oops I meant the 79 was crank rated

 

[sfara002]

Thanks for the replies, jimmbo, I plan to do the very same thing you are doing. I just dropped in a 115long block if you will and just ordered a set of wmk-41b carbs. Hoping to pick up some power. After inspecting the carbs, I noticed one of the backdrag/ economizer 90 hose fittings are broken. I plan to plug it but faztbull did you still have any elbows left? I noticed in another thread you mentioned you had some for another member. Thanks!

 

[Faztbullet]

Unless you install ported pistons,open reed stops all you will still have is a 90HP ......

 

[sfara002]

Faztbullet,

I think "block" was an inaccurate description. I installed a complete 115 engine as an assembly with pistons, intake, flywheel etc. (minus carbs/ingition) in place of my 90 hp. I already have switched over the ignition, no issues there. The final piece will be the carbs which didn't come with my engine I didn't figure my WMK-27 carbs from my 90 HP will work just by changing the Jets to .074 so I picked up a set WMK 41-1B carbs but ran into a couple road blocks with the carbs I picked up, first on one of the carbs the 90 degree plastic elbow from the backdrag/economizer hose to carb housing is missing. Not a huge deal since I had planned on plugging them anyways and pulling out the bowl vents. Second, it looks like the top Carb is missing the inlet tube referred to as the air bleeds and they feed air into emulsion tubes. After seeing what issues were found with the same problem here:

http://forums.iboats.com/forum/engi...r-outboards/632750-115-hp-in-line-6-carb-pics

I don't suppose I am able to replace that tube without buying a whole new carb (Bummer). So I think I will be in search of a WMK-41-1B TOP carb, part number I think I will be looking for is 7472A27.

 

[jimmbo]

Thanks for the replies, jimmbo, I plan to do the very same thing you are doing. I just dropped in a 115long block if you will and just ordered a set of wmk-41b carbs. Hoping to pick up some power. After inspecting the carbs, I noticed one of the backdrag/ economizer 90 hose fittings are broken. I plan to plug it but faztbull did you still have any elbows left? I noticed in another thread you mentioned you had some for another member. Thanks!

No I traded the 78 90hp on an 84 115hp in 1984
As I said there were other differences between a 90 and a 115. even more so since your 79 is crank rated and the 84 is prop rated

Just plug all the back drag hoses with little ball bearings. You can leave them unattached to the fuel bowl, but plug the hose going into the carb body. The Back drqg carb was an attempt to increase non-WOT economy by reducing atmospheric pressure in the fuel bowl. It worked well until Gasoline was reformulated to include oxidizers, then the mix was too lean. Leave the bowl vents alone!

 

[jimmbo]

Unless you install ported pistons,open reed stops all you will still have is a 90HP ......

Not only pistons and reed stops, the reed blocks and reeds themselves are different, as are the exhaust tuners, and even part of the throttle linkage(cam) are different.