'96 Merc 115hp - Shop says it's "fixed", but Still runs rough

[worktofish@hotmail.com]

I have a '96 Mercury 115 hp 4 cylinder on a 18' welded aluminum NW Jet fishing boat. I have had this for 20 years, and this motor has been almost completely trouble free. Early this summer, it started to stall out, so I replaced the fuel pump, to no avail. I then took it onto a shop, and a mere 5 weeks (!) and $1350 later, I picked it up. They rebuilt the 4 carbs and drained the fuel.

I did a test run, and the engine started great, but it shakes tremendously, causing the whole boat to shake. There's also a lot more exhaust smoke coming out of it. I took it back, and they claimed to fix it after week in the shop. However, it runs the same.

I called back, and asked them if this was "normal" in their opinion, and they said they have a shop boat, and its just how theirs runs. I have an appointment to get it into another shop in September, but my summer of boating is shot.

Can you tell me, based on these videos I took of it, if the shaking and exhaust levels are "normal" for a warm summer day? It's not as I recall, but would appreciate opinions from others before I take it back or drop $10K on a new motor.

 

[worktofish@hotmail.com]

Here's a 2nd video from another angle.

 

[racerone]

The first thing to do is a compression test ---Post your numbers here !!----Hard to find a competent shop these days I think ?

 

[Texasmark]

If you were running the boat regularly and it ran fine and all of a sudden it started acting up, with you running the boat in the same fashion as you had over the years, first thing I would look for would be fuel related problems, and that would start with bad fuel on the last fill up. I'd find a separate tank with fresh fuel from another source, drain the carbs and start over. In draining the carbs. the high speed jet is in the bottom of the bowl and is accessible from the port side...no need to remove anything other than what might be in your way to access the screws.....reason is to get the fuel out of the system and if any water, get it drained out before filling the carbs with fresh fuel.

Next I would explore the fuel lines, both between the tank and engine, and internal looking for tan crispy chips, some maybe semi-circles the diameter of your tank to engine fuel line; black specks. If you haven't changed fuel lines on that boat since new and used ethanol fuel, if you found what I mentioned time to do something is now, both types mentioned with a new bulb. I would replace your large fuel filter, port side, aft of carburetors. After removing the old one, cut it open. Tell us what you find and how much. If you find what I mentioned above then new lines are a must.

Next thing is when is the last time you put a kit in your fuel pump. If eons ago time to do that...course in the interim, if you used the sqeeze bulb and it cleared the problem, then the fuel pump kit will be a necessity for sure.

Next is when is the last time you changed spark plugs and what is their present condition?

I like to go after the easy stuff first. Never know what you'll find.

 

[worktofish@hotmail.com]

Well that was a good idea. The spark plugs were loose in the cylinders - I could move both directions with my fingers. I had installed a new set myself before I took it in, but they must have done their own compression test but never torqued them back down. Maddening...

Here are the numbers (top to bottom, I don't know the numbering system):
- 110 lb
- 110
- 100 (got a 105 reading too)
- 115

 

[worktofish@hotmail.com]

Texasmark - great advice. For background,

- My boat did run well a couple of times this year (June) then it acted like it was running out of gas. I had fuel from last year in the tank, but I had added new fuel each time out, so it was a mix of the two.
- I first replaced the fuel/water filter, plugs, and fuel line - no improvement
- I then replaced the fuel pump and fuel filter - no improvement. It did improve when I squeezed the bulb though
- At the mechanics shop they pumped the old gas out and rebuilt all 4 carbs. Now now issues with it seeming like it was running out of gas, it just runs really rough, in my opinion.

From the video, is that operating normally???

 

[racerone]

The top 2 carburetors have adjustable low speed mixture screws.----Have you tried adjusting them ?------Sudden change in motor operation would have me remove the exhaust covers to inspect pistons / rings.----$40 on gaskets is cheaper than 1/2 hr labour at the boat shop.------You do install a new impeller in the water pump every 5 years I hope !!!----And you have checked oil pump output per the manual every other year I hope ?

 

[worktofish@hotmail.com]

Racerone -

I have not adjusted the carburetor mixture screws as it's been some years since I have dealt with carbs. In talking to the mechanic, he said he set the mixture rich, which could be the issue. I'll check for posts on how to set them, but if you have any links I would appreciate it.

I replace the water pump impeller every 2 years, and it's strong, but I don't think that would impact engine smoothness.

No, I have not checked the oil pump output. Even the mechanic said he doesn't mess with the oil mixture. I'll dig through my manual to see about the settings. If anything, it seem to be oil rich given the smoke levels. I'll dig into it further and let you know what I find out.

Many thanks for the help!

 

[worktofish@hotmail.com]

Oh, and do the compression numbers seems OK? If so, I would think the rings are okay as well