50 hp OMC triple vibration at lower rpm

[ShoestringMariner]

Hey guys, having some troubles with a 50 hp three cylinder OMC. 1995. I rebuilt the curbs hoping it was a fuel delivery issue. New fuel filter. Was running out of sunlight tonight so I took it out for a quick spin. I didn’t get a chance to spark test. Extremely busy these days
And it was a scramble to get this part done anyway, what are you guys think I’m looking at ignition or could there be something bent like an output shaft? It feels like a strong shudder vibration

It starts and idles fine. A little bit chuggy during the idle/ slowest troll But does not stall. As soon as you give it any bit of throttle out of dead slow troll it starts to chug. Like it’s missing. I continues and gets a little bit worse until it gets on plane. Then it takes off and run smoothly and quietly.

When I get home I’m going to do a spark test. But I took a video tonight to see if any of you guys can tell by the sound for the pattern whether something is bent.

Oops video is too large. Any idea how I can shrink a video file? Any other means to post? I only have a phone

 

[tphoyt]

Definitely do a spark check you may have dropped a cylinder.

 

[ShoestringMariner]

Definitely do a spark check you may have dropped a cylinder.

Thanks I will. Too late tonight. I’m up at 4:30 for work.

If I have a bad spark, what might be the most logical culprit to check be?
Do coil packs go bad?
Stator?
Plug wires?
Other?
Plugs are new.

Could it be something in the advance?

Full out I got 30mph in a 15.5’ fiberglass deep vee. Kind of underwhelming but I don’t know if that’s typical for the HP vs hull shape/length

 

[flyingscott]

Check your stator and flywheel. Do a compression and spark check. Is the link and sync correct? Outer layer still on the cam roller?

 

[ShoestringMariner]

Thanks!
Compression is 105-110 I think or 110-115 (it has sat a few years since I did it so I’m a bit foggy. It is in that range, all cyls close. I did link and sink by manual. Checked timing mark on flywheel with piston stop. It’s bang on. I think cam roller is good. Black plastic sleeve on it.
Reading into stator/flywheel check. I did swap flywheels due to chipped teeth i
In starter locations. Looked good but I don’t know how tha check

 

[flyingscott]

Look for cracked magnets.

 

[tphoyt]

Just wondering if this just started or if its been going on for awhile?
May want to check your tank for water as well. A tiny amount of water in the bowels will can cause a bit of a shutter. It’s a long shot but worth looking at in my eyes.
And just for kicks how does your prop look? Any damage there that would make it off balance?
Best

 

[ShoestringMariner]

Just wondering if this just started or if its been going on for awhile?
May want to check your tank for water as well. A tiny amount of water in the bowels will can cause a bit of a shutter. It’s a long shot but worth looking at in my eyes.
And just for kicks how does your prop look? Any damage there that would make it off balance?
Best

New to me motor - first time setting up
Should be no water in the tank unless the fuel I got had it in it from contamination in their storage tank.
Prop is slightly worn, but ever so lightly, I will put on another to try.

 

[clemsonfor]

Hey guys, having some troubles with a 50 hp three cylinder OMC. 1995. I rebuilt the curbs hoping it was a fuel delivery issue. New fuel filter. Was running out of sunlight tonight so I took it out for a quick spin. I didn’t get a chance to spark test. Extremely busy these days
And it was a scramble to get this part done anyway, what are you guys think I’m looking at ignition or could there be something bent like an output shaft? It feels like a strong shudder vibration

It starts and idles fine. A little bit chuggy during the idle/ slowest troll But does not stall. As soon as you give it any bit of throttle out of dead slow troll it starts to chug. Like it’s missing. I continues and gets a little bit worse until it gets on plane. Then it takes off and run smoothly and quietly.

When I get home I’m going to do a spark test. But I took a video tonight to see if any of you guys can tell by the sound for the pattern whether something is bent.

Oops video is too large. Any idea how I can shrink a video file? Any other means to post? I only have a phone

Post the video on YouTube then post the link address here. The forum software will embed it in the post. If you have a Google account you basically just have to sign in to YouTube and just hit the upload button and select it. You can make it a private video if you want where only people with the link can see it...if you embed it here we will all be able to see it but it won't be searchable on YouTube if that's what you want.

 

[clemsonfor]

Thanks I will. Too late tonight. I’m up at 4:30 for work.

If I have a bad spark, what might be the most logical culprit to check be?
Do coil packs go bad?
Stator?
Plug wires?
Other?
Plugs are new.

Could it be something in the advance?

Full out I got 30mph in a 15.5’ fiberglass deep vee. Kind of underwhelming but I don’t know if that’s typical for the HP vs hull shape/length

Clunking isn't normal but that's about all I would think you would get out of a deep V 16' fiberglass boat with a 50 on it. Are you sure the lower unit is ok...clunking normally comes from there.

 

[ShoestringMariner]

Clunking isn't normal but that's about all I would think you would get out of a deep V 16' fiberglass boat with a 50 on it. Are you sure the lower unit is ok...clunking normally comes from there.

Thank you. No clunking. Just Chuggy

And good to know that that is the only performance I’ll get out of a 50. It doesn’t surprise me though. My waterlogged 16 foot aluminum super sport would go about the same speed with a 65

 

[ShoestringMariner]

Pulled the fly wheel. No cracked magnets. Stater coil looks good one spot looks like the paint was rubbed off. I think I’ll throw the old fly wheel on with the chipped teeth and try it. I have no idea or means to test the stater coil. I did find some crummy looking plug wires. One that had no continuity altogether so I threw on an old one that did have continuity. Slightly better this morning but still persisting. Dealer did not have stock on wires so I’m waiting for my order to come in. I’ll bet you that’s the problem.
Thank you for your help everybody. I will report back once I get my new wires on

 

[ShoestringMariner]

Strange thought. The fly wheel I picked up to replace the one this motor came with was from a 1993 60 hp. They look identical, But I wonder if there is magnet differences. I will find out tomorrow when I’m back on the water.

 

[clemsonfor]

I can't say for sure but I would put money on that they are the same flywheel. To confirm this look up each flywheel on your favorite parts website and see if it's the same part number?

But yes if you have a plug wire without continuity that for sure will give you poor performance cause that spark is having to just a gap before it gets to the plug and maybe not even fireing every time which would give you a shake from the miss.

 

[Silvertip]

If it runs fine after "clearing itself out" that suggest your carb rebuilding process was done wrong or the idle mixture screws have not been properly set.

 

[ShoestringMariner]

I can't say for sure but I would put money on that they are the same flywheel. To confirm this look up each flywheel on your favorite parts website and see if it's the same part number?

But yes if you have a plug wire without continuity that for sure will give you poor performance cause that spark is having to just a gap before it gets to the plug and maybe not even fireing every time which would give you a shake from the miss.

I put on a used wire from a parts motor and it was marginally better but just. I’ve ordered new ones. Dealer said obsolete so bringing in Seirra replacements. Why obsolete already?? Gotta be 10 million of these OMC triples still in use out there. Sheesh.
I hope the new wires are the answer…

 

[ShoestringMariner]

If it runs fine after "clearing itself out" that suggest your carb rebuilding process was done wrong or the idle mixture screws have not been properly set.

This was exactly my thoughts before I rebuilt them. They were spotless inside so the PO did them. I did them again. Idle screws exactly 2-3/4 turns out on all 3

 

[ShoestringMariner]

Guys I need help with this one still. Spark strength was 1/2” on 2 cyls, but about 1/4 to 3/8 on bottom.
3 new plug wires later, same issue. Switched out a coil pack for another used one, same performance.

My head is back to a plugged low speed circuit.
Idles fine in gear. Can slow troll all day. Anything between slow troll and giving it 60-70% throttle and it shakes like hell. Like bad

But if it is a plugged slow speed circuit why does it idle well?

I’m pulling my hair out

 

[racerone]

Cylinder sleeve rotated ?

 

[ShoestringMariner]

Cylinder sleeve rotated ?

What???
Help me out here man…You dont put a ton into your your explanations but I need you to