OMC 1994 120 to 140 conversion

**JohnT 1124** · 09-09-2017, 01:37 AM

Hello ,To all

Been lurking around playing with different motors over the years , so like anything I own it never seems to stay stock for very long I always seem to mod my motors in one from or another , I'm just trying to come up with the best plan, so here we go.
I just recently picked Javelin 379 that has 120hp Evinrude on it , I was looking into converting it a 140hp , The most I've seen so far is that reed blocks are different and the jets in the carbs are different not sure about the ports , I have read through a bunch of threads but haven't come across this year and conversion that I'm looking at doing.
If I add CCM reeds to my reed blocks would I seen increase in horsepower (I,E RPM ) or it will be so little it's not worth it , or would it be better to change reed blocks and jets to 140hp with CCM reeds to see increase with HP ? I feel like the boat is a little sluggish coming out of the hole, but the prop seems to give me pretty good top end. I notice if I come into a corner towing a tube a little slower for the younger kiddos it has a tendency to drop off of plane , then you need to jab the throttle to get it back on plane.
I mostly use the boat for ski and tubing with kiddos and fishing for me when they are done playing.
Or just scrap the 120hp and go to 150hp ?
Any thoughts ?

**phillnjack** · 09-09-2017, 04:02 PM

Vent the prop if its not vented already for the hole shot. put a foil on to keep on the plane at slower speeds.
the CCM reeds will smooth things out a lot nicer and maybe a touch on rpm.
But venting the prop and a foil is the things for holeshot..

what prop are you running at the moment on this motor.?

**faztbullet** · 09-09-2017, 10:56 PM

Slap the 150 on it

**JohnT 1124** · 09-09-2017, 11:34 PM

It's stainless steel , I'm wondering If there is not a hole in the prop about how big will it need to be ? I forgot to get the size off of but I will look today , Do you think its worth the extra effort to change reed blocks to 140hp I believe they are a 6 pedal design vs the 120hp is I believe 5 pedal design or I may have that backwards , either way will I see and increase power one over the other , or even going to v6 carbs ?
Is there one brand of foil better than others ? What about jack plate will it help , that is one add-on I never purchased for a boat.

**JohnT 1124** · 09-09-2017, 11:35 PM

I thought about just throwing a 150hp at but so far haven't ran across one for a reasonable price .

**skeeter91** · 09-12-2017, 09:16 AM

imho, most foil fins are at best, a band-aid for a incorrect setup.

**eli** · 09-13-2017, 04:13 PM

you will need exhaust plate tuner from 140 they are completely different from 120 i have both mids here

**powerabout** · 09-13-2017, 07:23 PM

Originally Posted by eli

you will need exhaust plate tuner from 140 they are completely different from 120 i have both mids here

I think it depends on the year, later are the same I think?
What year 120 are we talking?

**JohnT 1124** · 09-14-2017, 05:54 PM

Yes I agree with you Skeeter91 , I'm not a huge fan of hydrofoils myself , don't get me wrong I would be willing to try if it would not takeaway from my performance , I have tried them on lower hp motors and it left like the extra drag it was putting the boat it really wasn't worth it , that why I was kicking around the idea of a jack plate to see if could use that to help keep the boat on plane at slower speeds in the corners and over running , anyways its 1994 120hp , it has 14.25x 19 stainless steel prop it has a vent hole in the prop .

**powerabout** · 09-14-2017, 07:36 PM

94 120/140 adapter and megaphone are the same according to the parts book
so its just inlet and reeds ( and jetting)

**JohnT 1124** · 09-14-2017, 07:56 PM

So then all need to covert it to 140 is reed blocks and the different jets what about adding better reeds from CCM ?

Apparently someone changed the lower unit it looks to be larger gear case it's 4 3/4 outside diameter.
Not sure if that makes any difference in gearing , not a hundred percent sure how to check without tearing it apart.

**powerabout** · 09-14-2017, 08:05 PM

yes sure use CCM reeds just explain to him what the intended use of the boat is.
Be careful as 94 had a running change of linkage and airbox cover parts to another style

Your gearbox could have either v6 ratio or the original v4 ratio as that case came on the first engines.

**JohnT 1124** · 09-14-2017, 09:01 PM

Well after Irma went through the Keys I was even wondering if he open yet probably still trying to dig out , he is in Key Largo right? As far as things go I would like to get the most out the engine without totally making it worthless to just cruise along also , I know it sounds funny but I'm the guy that got his hair on fire most of the time until the wife and grandkids want to just go for a cruise .

**phillnjack** · 09-15-2017, 05:58 PM

foils are nothing to do with bad set up on most of the boats they are fitted to.
Plenty of boats on here that are set up very nice and use a foil. many have the Allison design and are pretty nice rigs.
have to also remember this is a bass boat not ultra lightweight paper thin race boat. so probably got a lot of weight on the bum.

**MattGreen** · 09-15-2017, 08:01 PM

OK, here's some clarifications:

- The 120 to 140 conversion for most model years is the reed block, intake manifold, and jetting. 5-petal on the 120, rubber-coated 6 petals on the 140 (same as the V6 and V8 use). You aren't going to see a massive speed increase - a few mph on a lighter boat.

- As Powerabout said, the 120/140 of the same year use the same megaphone/tuner. However, there were a couple different styles over the years and they are definitely different (the early one uses an inner liner, the later one does not).

- In 1993(ish) they went to a very ****ty carb design with needle-valve idle air bleeds. You can identify this because it still has the big air box but it has little plastic plugs to allow access to the needles with a screwdriver. If you're going to the effort to to intake upgrades you may as well toss these carbs if you have them and either go to the older fixed-jet style (easy), or the latest style with the idle fuel needles (potentially more complicated since they were not intended for that airbox). V6 mid-bore carbs are basically the same as your V4 so there's no speed to be found there in your situation. And you don't need the V6/V8 big-bores by the way.

- Again, if you are going to all this effort you may as well port and epoxy-sculpt the 140 intake you put on (either the rounded 80s style or the diamond-shaped later model ones). Don't use one of the "brick wall" ones from the early 1990s.
- Yes, you may as well also get a good set of reeds.

Matt