1989 Mercury 80hp Upgrade

[Glastron1987]

Recently I inherited a 1989 Glastron CSS16, with a 1989 Mercury 80hp (3 cyl. serial# 0C105001). I know some of you will say that this a great package, except there are 3 cylinders missing.

Well with just a little maintenance (e.g. spark plugs, one spark plug wire, oil lines) the engine fired right up and sounds great out of the water.

Before I take it for a real test run I’d like to give the carbs a good cleaning to avoid any issue…not because I don’t think it will run well, but more to ensure the engine doesn’t go lean and burn up.

So I am thinking that this is the time to make some power improvement as well (e.g. carbon reeds and upgraded carbs). The only differences I see on the parts websites between the 70, 75, 80, and 90 of the series are the carbs, and in some cases the tuner.

My question relates to the carbs upgrade… instead of buying new carbs, can I just reject the carbs I have with the 90hp jets? My current carbs are cast with the WME designation; listing for the 90hp carbs indicates some are WME-10. So I think this would work, and give my 90hp. Anyone know about these things?

[JPEROG]

Adding more fuel to an intake system that doesn't have a provision to also allow more air will get you a negative result (it will just be rich). You always need air and fuel together. My guess is that the higher output motors had larger carb bodies.
A little compression, a set of reeds from Chris Carson here on the board, increased air intake via air box modification or cowl modification along with a couple additional holes above the cavitation plate for exhaust relief and corrected jetting will be your easiest gain on that little motor.

Joe

[Capt.Insane-o]

There is very little that can be done effectively to those motors. Run it and enjoy it until the end.

[FMP]

Would the four cylinder 125 carb help? Same reed assembly, lots of holes to work but is it worth it to open them any and just have enough to keep the reeds happy? Maybe cleanup to the tranfers etc, means taking it apart. Then a touch more area on the ex ports, not sure what they look like but maybe cut a bridge out with a little squaring. Blind hole motor I believe so resist raising them more than a touch with good chamfer.
Will it tolerate a hair more ign timing with your fueling?
Maybe some setup height, prop or even a few inches setback?

[Glastron1987]

By corrected jetting do you mean change the main jet from the .064 to something like the .070, but only after mods to the the air box/cowl/exhaust holes?

Adding more fuel to an intake system that doesn't have a provision to also allow more air will get you a negative result (it will just be rich). You always need air and fuel together. My guess is that the higher output motors had larger carb bodies.
A little compression, a set of reeds from Chris Carson here on the board, increased air intake via air box modification or cowl modification along with a couple additional holes above the cavitation plate for exhaust relief and corrected jetting will be your easiest gain on that little motor.

Joe

[Glastron1987]

I'm not really prepared to do machine work, just looking for simple things while I have to clean the carbs. So things like reeds, stuffers, jets and maybe new carbs (not sure about the 125's but that's a good thought) would be OK. Its actually torque for pulling up skiers that I'm looking to improve.

Would the four cylinder 125 carb help? Same reed assembly, lots of holes to work but is it worth it to open them any and just have enough to keep the reeds happy? Maybe cleanup to the tranfers etc, means taking it apart. Then a touch more area on the ex ports, not sure what they look like but maybe cut a bridge out with a little squaring. Blind hole motor I believe so resist raising them more than a touch with good chamfer.
Will it tolerate a hair more ign timing with your fueling?
Maybe some setup height, prop or even a few inches setback?

[FMP]

The 125 carbs are wme 90 or something I forget. On the four, it has 4 carbs but that motor also shutsdown 2 cylinders at troll, not certain all four carbs are exactly the same but probably. Likely a bigger venturi than your carbs, check it out if they have the same ears to mount. But on their own without additional porting you might not get all the advantage of them. What's the displacement , bore is 3.375" I think, what's the stroke, same as cylinder ci as the four?

Extra one to go ape with
https://www.ebay.com/itm/876-8947A23...e/401915151723

A good lower pitch ski prop is easier.

[SS Minnow]

I'm not really prepared to do machine work, just looking for simple things while I have to clean the carbs. So things like reeds, stuffers, jets and maybe new carbs (not sure about the 125's but that's a good thought) would be OK. Its actually torque for pulling up skiers that I'm looking to improve.

If you are looking for torque, do not go with bigger carbs. Bigger carbs are more for top end then anything, and by changing carbs you are opening up a big can of worms. If I were you, I would get new reeds, lap the cages, and if stuffers are available for your motor, get them. If not, you can make them. At that point, you still would not have to worry about jetting the carbs as you have changed nothing that would require you to do so.

If that still is not enough power for you (and it never is) you can look into air box mods and having the heads milled down for more compression. Either of those mods or combination of will require you to change the jetting or you will be too lean. Air box mods can be as simple as removing a piece, drilling some holes, or totally removing it. Depends on what exactly you have, and I am not familiar enough with it to tell you. As far as having the head milled, first you have to find out what your compression is now, and then have the head cc'd to determine how much you would want to knock it down. You may need more work then that to make sure the head works with the pistons, as am not sure with your motor, I will not even try to tell you. A reputable machine shop will know though. Worth noting that if you do increase compression, at certain points you need to have higher octane fuel. If 91 is not readily available, you might want to re-think raising compression.

If what you really want is more low end, that is basically the order in which I would go looking for it. Trying to find a bunch of top end from an 80hp would be an exercise in futility in my opinion. So much easier to just go and buy a bigger motor and start from there. Plenty of old outboards on the market now.

[JPEROG]

By corrected jetting do you mean change the main jet from the .064 to something like the .070, but only after mods to the the air box/cowl/exhaust holes?

Yes, you will have to take spark plug readings and watch the wash pattern on your pistons to get it correct but any of those changes mentioned will all require more fuel.

Joe

[Glastron1987]

Thanks for all of your comment and suggestions….

On my 80hp the bore is 3.38 (i.e. 3.375) and stroke is 2.65, the same as the 90hp for my model year (1989).
The 4 cylinder (115hp for this model year) is the same bore but its stroke is 2.93.

(Merc moved to a bore of 3.5 in later models for the 3 and 4 cylinder motors, just like they moved from 2.4L to 2.5L V6 engines which have that same bore as these 3 and 4 cylinder engines)

I am not interested in any cutting, machining, or drilling, and maybe I’m boring, but want to stick with regular gas.

So looking at the part listings with all the combination of carbs, jets, blocks, and tuners that go into making the engine a 70, 75, 80, or 90, and considering all of your comments it looks like my plan will be:

1. Keep the carbs as they are, just give them a good cleaning and rebuild
2. Upgrade the reeds to composite
3. Add stuffers if available
4. Put a good ski prop on

[FMP]

Just for kicks, the 125 carbs have a different throttle plate/valve part number than the carbs you have. They likely are a bit bigger, not too much I don't think, maybe around 32mm , just a guess. Maybe your plate has a stamp on it.

[SS Minnow]

Thanks for all of your comment and suggestions….

On my 80hp the bore is 3.38 (i.e. 3.375) and stroke is 2.65, the same as the 90hp for my model year (1989).
The 4 cylinder (115hp for this model year) is the same bore but its stroke is 2.93.

(Merc moved to a bore of 3.5 in later models for the 3 and 4 cylinder motors, just like they moved from 2.4L to 2.5L V6 engines which have that same bore as these 3 and 4 cylinder engines)

I am not interested in any cutting, machining, or drilling, and maybe I’m boring, but want to stick with regular gas.

So looking at the part listings with all the combination of carbs, jets, blocks, and tuners that go into making the engine a 70, 75, 80, or 90, and considering all of your comments it looks like my plan will be:

1. Keep the carbs as they are, just give them a good cleaning and rebuild
2. Upgrade the reeds to composite
3. Add stuffers if available
4. Put a good ski prop on

This is the parts site I go to for part diagrams, numbers etc:

http://www.marineengine.com/parts/me...ts/sn/0C105001

From what I see there, 70 80 and 90 hp models have different carbs and different blocks. If the blocks are different it very likely means that the three have different port width or timing, maybe both. I am not that familiar with your motor so I could not say, but there is a reason there are three different blocks, and different ports is likely the reason. They do all have the same reed cages, and intake manifolds and that is a shame because I have seen changing those as an easy way to pick up a few hp on some motors.

So yeah, you have the right plan. Freshen up the carbs and reeds. Make sure you lap the cages. Stuffers if available, never heard of anybody not liking that upgrade. And of course, find the right prop for how you will use the boat. I have found many a good deal on used props on Craigslist and Facebook.

[Glastron1987]

This is what I see listed for the throttle plates:

For the 70/75/80hp is 9593 (should match mine as I should be stock)
For the 90 with the same tuner is it 9609.
For the 90 with a different tuner it is 814678.
For the 115 it is 813619.
…and for the 125 it is 97241.

No standardization as far as I can tell.

Just for kicks, the 125 carbs have a different throttle plate/valve part number than the carbs you have. They likely are a bit bigger, not too much I don't think, maybe around 32mm , just a guess. Maybe your plate has a stamp on it.

[FMP]

Yeah maybe 34mm for the 97241

Just tune it up solid and love it, don't forget the pump impeller etc if not done in a while.

Would be fun to try to build one for some power, bigger carbs, worked transfers with a bit more duration, a little more duration and area on exhaust, some chest work and through to tuner to carry some more volume.

Or the option to swap motors

Just a personal thing here but a good couple videos, 125HP CHRYSLER style FORCE, weights about 269lbs with trim tilt and a ss prop, the 3 cyl 85/90 245lbs.
Here they were testing ski props and swapping lower units 1.73:1 to 2:1 , powerflow side bullet pickups.
Heavy boat, only lost 2 mph with the 2:1 setup
If you could find such a solid clean example to about year 91/92 with the CHRYSLER style leg it weighs about the same or a touch more as your Merc and will out perform it no doubt, JMO.

Again the difference in props and gearing, which is what your trying to do for skiing.

https://m.youtube.com/watch?v=3ufBl6IcZPI
https://m.youtube.com/watch?v=wBs_MZVTzok
https://m.youtube.com/watch?v=Fc-u81IwDdI

[Glastron1987]

Got the new composite reeds installed and the carb rebuilds. Started right up afterward.

One thing I noticed on this 80hp compare to the V6's I've worked on is that there is no bleed system. Any reason engines like this 80 can get away without one?