Mercury 80 hp 3 cylinder 2 stroke

[Henry D]

I have a new to me 17 1/2’ center console

power is a Mercury 80hp 3 cylinder 2 stroke

Motor starts right up every time

idles at 800 RPM

Trolls pretty well

 

when you accelerate to get up on plane everything goes well to about 3300 RPM then the motor seems to bog down and that has been repeatable with the exception of once it actually planed out and reached 5100 RPM

 

I have run it off a remote fuel tank

Primer Bulb an fuel line to motor is new

compression is between 110 and 115 across the 3 cylinders

i emptied the fuel tank and have been using only non ethanol fuel treated with SeaFoam since I purchased it

fuel filter replaced twice

plugs replaced

ignition wires replaced

 

 

I also have observed fuel in the well in front of the motor after I tow the boat home even though I disconnected the fuel line and let the motor run itself out of fuel before I put it on the trailer

 

So I’m looking for next step recommendations 

carb rebuild & cleaning ?

timing ?

Stator ?

I appreciate the experience and knowledge of the community and look forward to your recommendations thanks

Henry

 

[LongLine]

Check the small hoses and fittings between the fuel pump and the carburators.  They may be cracked, deterioated or loose.  If in great condition then go after carburtors.  You're leaking fuel & sucking air someplace.

[sherman brown]

sounds to me like you may just be over propped. 5100 RPMs at WOT sounds like it isn't getting enough RPMs. what are the max RPMs for your motor? before tearing into other things I would try to find a prop 2" less pitch than the one you are using now. If it's a 19p go to a 17p and so on. going down 2" with a 4 blade would be even better. but going down 4" may be needed to get more RPMs because the extra blade makes it harder to turn than a 3 blade.

 

and if the gas line is old it wouldn't hurt anything even if that's not your problem, as it might save you a big problem later.

[Henry D]

Hi all am currently replacing fuel lines and clamps they were secured with Ty wraps and some were not exactly what I would call tight

i should clarify the fuel that I find in the well on the back of the boat is not from a fuel line leaking, even when I run the boat out of fuel by disconnecting the fuel line after towing home at highway speed that’s when I find the fuel 

Is it possible that I have a float in one of the carbs sticking and that cylinder is flooded also resulting in the lack of performance?

Mercury lists WOT at 4750 to 5250 for this motor from the info I’ve been able to find

the prop on it is a 13 3/4  x 15 pitch so based on seeing 5100 rpm the one time it ran what would your thoughts be

I really appreciate all your input 

[LongLine]

Guessing that you tow with motor tilted up.  Even though you run engine till it stalls with fuel disconnected, there is still some fuel in the carbs that could leak/pour out on the way home.  (although you'd think it'd evaporate.)

 

Check for good/consistent spark on all 3 cylinders before you pull carbs. 

[Great_Laker]

First problem is it’s a Merc, trade it in for any other brand and that should fix it. Second, check to see if each cylinder is firing correctly. You can troll on two cylinders without noticing a problem, it’s only after you hit higher RPMs that you will notice. Check plug wires, plugs, power packs. Hope it’s an easy fix! 

[rolmops]

I had the same engine and I had similar problems. It seems that these engines have a "dead " spot while accelerating. You can rev it up real slow and you will see that that your problem is very clear as you described. The engine does not get enough fuel at that rpm to properly accelerate . There are two ways to overcome the problem. the first is giving it a bit of choke as you near the trouble rpm The second is to slam the hammer down to full speed as you near the trouble spot. That often helps getting it over the bump..

Let us know if that helped

Edited August 6, 2023 by rolmops

[Henry D]

I just finished replacing the fuel lines from the quick connect to fuel pump and out to all 3 carbs

i have replaced the ignition wires (plug wires) checked the resistance of all 3 coils & through the plug wires everything is even across the 3 coils

I have to get an inline spark tester would be able to use it in the driveway 

I really appreciate the help I’ll keep you posted

[rolmops]

If neither of those tricks help your fuel pump may be under performing. There may be a tiny leak in the diaphragm or a dirty fuel filer which is in the pump.

[LongLine]

Did you replace the disconnect fitting?  Older Mercs had that huge push & twist style "pain in the butt"fitting.  They had a O-ringaround the ball inside & if it didn't seat right the dag-gone thing would leak.  

[Henry D]

The disconnect fitting is the up to date

I have not gotten into the fuel pump as of yet I wasn’t aware of a filter inside the pump itself I can’t imagine replacing the diaphragm in the pump can be too bad is the filter cleanable or replaceable 

I guess I’ll have to familiarize myself with the pumps inter workings 

Is there a way to check fuel pressure and what should it be or am I better off just rebuilding the pump

 

So my list grows 

I’ll give playing with the throttle and choke a try next time out

check spark across all 3 cylinders

and if the issue persists I’ll take a look at the pump 

Thanks for the help gentlemen I’ll keep you up to date

 

 

 

[rolmops]

14 minutes ago, Henry D said:

The disconnect fitting is the up to date

I have not gotten into the fuel pump as of yet I wasn’t aware of a filter inside the pump itself I can’t imagine replacing the diaphragm in the pump can be too bad is the filter cleanable or replaceable 

I guess I’ll have to familiarize myself with the pumps inter workings 

Is there a way to check fuel pressure and what should it be or am I better off just rebuilding the pump

 

So my list grows 

I’ll give playing with the throttle and choke a try next time out

check spark across all 3 cylinders

and if the issue persists I’ll take a look at the pump 

Thanks for the help gentlemen I’ll keep you up to date

 

 

 

You can just unscrew the the big bolt in the center of the fuel pump and you will find the filter screen right behind the cover. that is the easy part. If you take the pump itself apart do it on a large piece of cloth. there are a few very small parts in there. like a ball and a spring. Make sure you remember exactly where everything goes.  The diaphragm is very cheap , but people often end up buying a new pump. There are special tools to test fuel pressure, but I never used one. It is just easier to replace the diaphragm. They usually look deformed when you open the pump.

Edited August 6, 2023 by rolmops

[rolmops]

Sorry these pumps do not have the filter inside. I got mixed up with the evinrude ones.

Edited August 6, 2023 by rolmops

[Shakemsam]

I haven't seen any mention of cleaning the carb(s). sorry if I missed it.  Sounds like the highspeed circuit. do a thorough cleaning or rebuild. I have never had an outboard that didn't drip fuel when left in the tilted position. it generally drips right from the carb throat due to the bowl being full.

[LongLine]

I read this as that you have an older engine with two issues.  1st being fuel in the engine well of the boat after you trailer it.  The 2nd being that it won't come up to full RPM when under way.

 

The 1st is that you have a leak some place in the fuel line or that the fuel line is not holding pressure. Check by disconnecting line from motor & pump the ball.  Should get really hard and stay hard. (Obviously no smoking when you do this)

 

On the 2nd:  As long as you have good compression and good strong spark across all 3 cylinders then the issue must be with the fuel or fuel delivery system.  I'm assuming you completely emptied the tank when you bought it. Sea Foam is good at dissolving "crap" in the tank; however, it will thin out any "sludge" (and may not dissolve all of it) which will get pumped into the motor.   What I do every couple of years is pump out about a gallon of gas from my tank FROM the bottom.  I made a simple pump by using a couple sections of hose and a fuel line ball between them and hand squeeze into a $7 clear cookie jar from walmart and look at it.  (Is it possible that you filled up tank, put Sea Foam in it then ran it before doing any of the other stuff?)

 

As you ran it on a separate tank but had the same low RPM issue, then the in-boat tank & fuel are eliminated while you ran it on the separate tank. (You also replaced those lines.  Older lines were not ethanol resistant & did deteriorate) You also said you replaced fuel filter but didn't say what you found in the filter.  This leaves the fuel pump, interconnecting fuel lines, carburetors, autochoke solenoid and the linkages between spark & carburetors. 

 

You replaced the interconnecting fuel lines & tightened them so they're eliminated.  I'm thinking linkage is eliminated because engine was not hard to start, rang at idle and didn't run rough up to 3300 RPM.   (Although 800 RPM idle seems a little high to me). However, you can research "Lync & sync" on internet for your engine. Check conditions of any rollers on the linkages. i.e grooves or flat spots.

 

If your fuel pump is weak, then next time you're out on the water, have someone pump the ball in the fuel line.  If no difference then I'd think there's a very good chance that your pump is okay.  (However, if it's the original pump, diaphragm might be thin, and I'd replace it for peace of mind.)  You might also try the autochoke when you get to that speed. 

 

This leaves carburetors.   Be careful removing them & observe if anything is in the bowls.  I.e particles, sludge, etc.  If original parts, float could be saturated (and not floating & out of adjustment) or spring & needles could be "sludged up."  If you've gone this far, it'd probably be best to clean everything & get rebuild kits that include float, spring, needle & gaskets.  If you found particles in the bowl, especially black ones, then something rubber has deteriorated, and you need to find the source.  

 

Electric start motors usually have an autochoke solenoid. When you have the engine off and activate the choke from the controls, you should hear a loud click from the solenoid.  It has rubber o-rings in it. Pretty easy to remove and check for deterioration.  Note" When you run the motor out of gas by disconnecting the fuel line, you should always wait a couple minutes then try to restart the motor fully choked to run gas out of it and its lines.

 

Unfortunately, B.O.A.T equals "Break out another Thousand."

 

Good luck & let us know how you make out.

[Henry D]

Hi guys I hooked up a in-line spark tool

& set up my phone on a tripod so I could video in a dark garage

The Top Cylinder looked very different (weaker in my opinion)  

 than the middle and bottom 

I then swapped the coils between the top and middle and repeated the test

this did NOT move the weaker signal to the middle cylinder

So at this point I would think I have an issue with the ignition control module

i tried to attach the videos but was unsuccessful so would I be on the right track replacing the module the coils are wired to or is there something else I can check at this point

Also if you have recommendations as to where your buying parts please send them along

The other issue I’ve run into is looking up this motor by its serial number it is Canadian built I’ll attach a photo of the serial number

 

 

 

 

 

 

[LongLine]

I've bought parts from marinenegine.com.  (Are you sure that's an 80 hp?)

 

Your coil to control module wire  and connection are good...right?

[LongLine]

On that site, you should be able to find a good drawing of your electrical system components.  Mercury may not call it a 'control module."  Might be called some kind of "switch."

[Henry D]

Not knowing the history of this boat 

I wouldn’t be surprised if it’s not a 80 hp (that’s the decal on the cowling) Mercury also made 75 hp motors on this 3 cylinder platform best I can tell its of a 1982 vintage although the serial number has a 75 in it and I don’t get an exact match up when searching on the serial # online

As far as the ignition issue I described in my last post  you’re correct I believe Mercury calls the control module the coils are wired to a Switch Box those wires all look okay 

I did check them for rust and broken insulation etc.I checked the grounds for continuity 

the anomaly I saw in the spark test tool on the Top cylinder is quite different from the middle and bottom cylinders and the fact I didn’t move the issue swapping coils makes me think the switch box is faulty I haven’t looked to see how much they are but I’m sure they’re not cheap

I hate just throwing parts at a problem not fully understanding the root cause 

Im slowly learning the ins and outs of this motor 

I really appreciate your knowledge as well as the other guys and your willingness to help me out

Thanks

 

 

 

 

 

[LongLine]

I don't see any serials starting with "0A75".  I don't know that mercury put the hp in the serial like Evinrude did.  I know that many parts on the Evinrude 3 bangers are interchangeable over the hps.. (but not all.)   Have you heard of the site: iboats.com?  Under the tab entitled "community" they have a forum category for Mercury repair.  I'd ask them for help on ID, troubleshooting & parts info.  Some of those guys are very helpful.  

[Henry D]

I’ll check it out thanks

[Henry D]

I sent a email to marineengine.com

they responded with no results on that serial number too

[rolmops]

OA 7522171 is a 1989 3 cylinder 80 horse or a 75xd (same thing). Check it out on page four of this attached pdf

Mercury63_92(2).pdf

Edited August 12, 2023 by rolmops

[LongLine]

So I read that, that the "0" in front of the "A" isn't used in serial lookups.  And the A752171 is the same as the 9549689 (Belgium) and C100000.   (Does motor look like this?)

 

[lost a lure]

Is there a model number on a sticker on the engine?