1993 Mercury 115hp - sputters under load - low top speed

[Slayer412]

I recently bought a 1994 Skeeter SS90 with a 1993 115hp Merc. The previous owner said the motor starts and idles fine but when he tries to plane out, it just sputters and misses.

I got it out for the first time today and he was somewhat right. It starts and idles, and it does more of a sputter rather than a miss. I feel like it might be more of a fuel issue rather than a stator or something electronic.

I was able to get it up on plane and once it’s there, it just purrs and seems to run absolutely perfect.

I did about 10 hole shots and each time the sputter got just a bit better and shorter and the boat seemed to plane out quicker.

Prior to running it, I removed the gas tank and cleaned it out and put new gas in. My next step will be a fuel filter and possibly a pump if the filter doesn’t fix the problem.

The next problem I have is the top speed. It’s a tiny boat and I could only achieve 31mph. This is odd considering how smooth and healthy the motor seemed to be once on plane.

The boat for some reason has a 5 blade prop. I’m not sure if that would be the issue or not? I know the RPMs would be crucial to help solve that issue, but my tach doesn’t work.

Any input on either of my issues would be appreciated.

From the research I’ve done, the 5 blade would be more of a hole shot prop. I’m thinking I may have a slight fuel shortage under load and my motor doesn’t have enough juice to spool that 5 blade prop up while trying to plane out. This would also explain the miserable low top speed.

Tell me if my thinking is way off!

[06 SB]

You are going to need to post the motor’s serial number for the experts to help.

There can be multiple “1993 Mercury 115” motors. Is it an inline 4 cylinder? Did you replace every inch of fuel lines?

The 5 blade prop definitely hurts top end. What is your max RPM with this prop?

[Slayer412]

You are going to need to post the motor’s serial number for the experts to help.

There can be multiple “1993 Mercury 115” motors. Is it an inline 4 cylinder? Did you replace every inch of fuel lines?

The 5 blade prop definitely hurts top end. What is your max RPM with this prop?

Serial Number - 0D230886

4 Cylinder

Oil injection has been removed

RMPs are unknown due to my tach not working. With my “general” knowledge/experience with 2-strokes, it doesn’t sound completely tapped out. It sounds like there are more RPMs to gain, but at the same time it’s not bogged down. It purrs nicely once on plane, just slowly.

[Slayer412]

And no, I have not replaced all of my fuel lines yet.

[EuropeanAM]

Really need to get an accurate tach on it.

Additionally: Need to check the BASICS: Compression Test, Spark Test, Fuel Quality/Delivery tests.

Make sure that BOTH fuel filters inside the cowling have been replaced (and you may need to rebuild or replace the accelerator pump).

[Slayer412]

Compression is good on all 4 cylinders and the fuel is brand new, mixed with amsoil outboard pre-mix.

I ordered the fuel filters this evening! I’ll throw those on and give it a shot in a few days here.

[JOE54]

what pitch is that 5 blade , keep in mind that engine only idles on 2 cyls so it has a set of small squirters /injectors on the bottom 2 and a accelerator pump mounted on the side of block just above fuel pump these must work properly on this mtr or it will stuble on hole shot after that its on the carbs ,;;;;; ps set up is critical on this engine for proper running , do not attempt to adjust this engine on hose put it in lake , they run very lean at low speed also

[Slayer412]

One more update...

I spoke to the previous owner who never got this motor/boat combination on plane. With the previous 1994 115hp, he said he was a 50mph boat with the 5-blade until he blew the engine and threw this 1993 on the boat.

This new motor sits further in the water and he removed the 3-blade it came with and installed the 5-blade. I'm not sure either how much difference the prop would have sitting a bit lower in the water.

[Slicefixer]

what pitch is that 5 blade , keep in mind that engine only idles on 2 cyls so it has a set of small squirters /injectors on the bottom 2 and a accelerator pump mounted on the side of block just above fuel pump these must work properly on this mtr or it will stuble on hole shot after that its on the carbs ,;;;;; ps set up is critical on this engine for proper running , do not attempt to adjust this engine on hose put it in lake , they run very lean at low speed also

Excellent advice (no surprise coming from 54) and exactly, to the letter, of my experience with the 2x2.

[Slayer412]

Ok! Got the prop off and it happens to be a 13” 26p 5-blade.

The previous owner also gave me the prop that came with the motor which is a 13.75 15p 3-blade.

My tach is supposed to be delivered today and I’ll give it a run with the new fuel lines and fuel filter.

[JOE54]

on that boat that engine should sling both those outa sight /rpms , recommend seeking very experienced tech on this engine ;;;; youll have to set tach more than likely

[Slayer412]

Ok, so I got my tach installed and took the boat out with the 5 blade. Night and day difference… with the 3 blade, the holeshot set me back in my seat and it seemed to plane out within 2 seconds or less. I didn’t have my tach on for the 3 blade though. I switched back to the 5 blade and the issues it was having by sputtering and missing under the holeshot all came back. My RPMs were right around 3200 at 30mph. I couldn’t get the speed or the RPMs any higher than that.

[Slayer412]

I’ll have to change the prop and check the RPMs. With both props I’d stay around the 30mph mark. The 3-blade 15p didn’t cause my motor to sputter or miss and the holeshot was absolutely amazing.

[Slayer412]

Took it out with the 3 blade 15p. Speed was down to about 24-25 and RPMs were around 4400.

[EuropeanAM]

What tachometer (specifically) did you purchase, and what settings did you make to the tach while installing it?

[Slayer412]

What tachometer (specifically) did you purchase, and what settings did you make to the tach while installing it?

I ended up getting a used one off of FB market place which was the same as mine with a similar motor. I didn’t adjust anything on the tach.

[Slayer412]

Carb1.png

[Slayer412]

The picture above is of my carb at WOT. It doesn't appear to be anywhere near enough. This could explain my inability to get the RPMs up...

Please let me know if this looks normal at WOT for an outboard. The old Yamaha Banshees I used to race opened up fully so this was a bit surprising to me.

[JOE54]

Ok! Got the prop off and it happens to be a 13” 26p 5-blade.

The previous owner also gave me the prop that came with the motor which is a 13.75 15p 3-blade.

My tach is supposed to be delivered today and I’ll give it a run with the new fuel lines and fuel filter.

that 26 pitch is not gonna work way to big , id be looking for somewhere in the 19- 21 range 23 max pitches

[Slayer412]

that 26 pitch is not gonna work way to big , id be looking for somewhere in the 19- 21 range 23 max pitches

With the previous 115hp motor and the 26p, the boat would run high 50s. This isn’t an 18’, wide boat, it’s a little 16’ SS90.The issue is within the motor. I can only get the engine to 4400RPMs with the 15p. Anything above the 15 and below the 26 will give me the same symptoms. The issue right now doesn’t seem to be the prop.