1987 2.5L Mercruiser inboard/outboard

[DanOnTheBoat]

Hi everyone, new here. Also a new boat owner. So I took out my boat, it has a 1987 Mercruiser 4 cylinder inboard engine. I took it out yesterday and drove it for about 45 minutes straight no stopping, was on plane cruising at around 2500ish RPM. I then started to feel and hear my engine slowly lose power and bog down until it cut out. I tried to fire it up it didn't. After about half an hour of waiting with the engine cover off, it fired right up like nothing happened. I then put the cover back on and headed back after about 20-30 minutes it did the same thing except this time when I felt it I opened the cover off of the engine while it was running and it it opened up and ran like it should. After that I ran the boat some more even getting into the 300-3500 RPM with the engine cover off and it did not hesitate nor lose power.

So I'm wondering could that be an engine air issue? I've cut a vent right infront of my engine cover maybe that would help.

 

[airshot]

Doubt lack of air being a problem, in all my years of boating I have never saw a doghouse sealed airtight. If nothing else, the blower ducts would be more than adequate. Look into your fuel system, a good chance you have water in your fuel. Your description sounds new very much like water in your fuel. Best bet is to pump out the tank, examine the fuel thru sampling in a glass container, sooner or later you will see the seperation. Do you have a fuel/ water seperator filter ? If not add one, if there is one replace the filter.
Don't just add an additive, best option is to pump put your fuel tank...if it were all good, you can put it back in. But...I will bet on fuel issues !!

 

[DanOnTheBoat]

The thing is I filled the boat up with fresh gas yesterday, I ran through half a tank of it. The engine wasn't running rough or anything it idled and accelerated like usual. I do have a brand new fuel/water separator that i have installed about a week ago, I've removed it yesterday to see signs of water or dirt, it was all clean. The carburator is also brand new along with the fuel pump.

 

[airshot]

Water is clear similar to fuel when looking into a small fuel filter. Hope you don't have water in your fuel, but your description sure sounds like it. Right after filling the motor usually runs good as the water has been mixed up from filling. After setting a while is when the water settles to the bottom where the fuel pickup sucks it in. Watch carefully where you buy your fuel, often the busy stations don't check their tanks and change their filters often enough. Looking forward to hearing if you found the problem..

 

[DanOnTheBoat]

Hm okay, I'll definitely look into the fuel. I filled it up at a gas station with octane 87, I heard it's okay to run mercruiser engines on that fuel but it's bad to let it sit. I live in Ontario, Canada and basically everywhere here the fuel has up to 10% ethanol. Do you think fuel stabilizer would help? If I fill up the gas tank and put stabilizer and go out for the day, would that be okay?

Also is gas station fuel okay? What fuel do you use in you're boat? Maybe higher octane gas with lower amount of ethanol?

 

[Faztbullet]

Is the carb OEM or aftermarket?

 

[DanOnTheBoat]

It has an aftermarket carburator. I still have the OEM one.

 

[Scott Danforth]

It has an aftermarket carburator. I still have the OEM one.

Amazon? if so, rebuild your original carb

 

[DanOnTheBoat]

Yeah, it was around $200 don't know if that matters. It wasn't anything cheap. I know OEM is obviously better but what is the difference? The new carburator that I have installed right now works great and has consistent gas flow.

 

[Scott Danforth]

I know OEM is obviously better but what is the difference?

I have pulled chinese made carbs apart to find metal shavings, etc.

 

[matt167]

I put a Chinese carb on my 3.0l as a stop gap since my original is missing parts of the choke linkage. It doesn’t scream quality although it does make the engine go vroom. It has a bad stumble

Your not getting a real carburetor for less than $300

 

[DanOnTheBoat]

Yeah I can tell quality wise there's a big difference with the OEM one. Mine is basically brand new it has less than 10 hours of use on it. I opened it up today and it looked clean inside. I tried installing the OEM carburator and it completely flooded my engine with gas. Had to take out the spark plugs and carburator to hopefully dry it out. Will probably install the new carburator on.

Also what do you mean by stumble?

 

[Scott Danforth]

I tried installing the OEM carburator and it completely flooded my engine with gas.

you have to rebuild the carb if it sat for more than a few months with fuel in it.

 

[airshot]

Hm okay, I'll definitely look into the fuel. I filled it up at a gas station with octane 87, I heard it's okay to run mercruiser engines on that fuel but it's bad to let it sit. I live in Ontario, Canada and basically everywhere here the fuel has up to 10% ethanol. Do you think fuel stabilizer would help? If I fill up the gas tank and put stabilizer and go out for the day, would that be okay?

Also is gas station fuel okay? What fuel do you use in you're boat? Maybe higher octane gas with lower amount of ethanol?

E10 fuel is fine, but yes, do run a fuel stabilizer ! Been using E10 since it came out with O issues, but you need to follow up with a stabilizer. At the end of the season, either fill your tank full or drain it dry. I would recomend using the 89 octane fuel....