Merc 1993 60hp 3 cyl. wont go past 3000 rpm... FINAL UPDATE!

[saumon]

I made this post to let you know what happen (and for helping others in the future):

Last week i was running for approx. 15 min at 5200 rpm then, suddenly, the engine drop at 2800-3000 rpm. It idle fine and can go to 5000+ rpm in neutral but stall at 2800-3000 rpm under load. I headed back home and, an hour later, i check the following:

As my rpm doesn't over rev, i know it isn't a spun prop hub, so it look like if i was dropping a cylinder. I then look at (from the costly source of problem to the cheapest):
1 - do i blow a piston? compression was not good but ok (betwwen 90-115 on all 3 cyl)
2 - do i need a new switchbox, or a coil? spark was also good on all three.
3 - i now know the problem is related to the fuel delivery system, hourra!

As the system is 13 years old, i changed the complete fuel line and bulb primer to eliminate possible air leak, then replaced the inline fuel filter. I also overhauled the fuel pump and will do the three carbs next week (most likely a plugged high speed jet, probably in the bottom carb by the very clean appearance of the related spark plug when compared with the two others).

I'll give you an update!

 

[rickdb1boat]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

very clean appearance of the related spark plug when compared with the two others).

Might be a bad head gasket letting water into the bottom cylinder. Let us know....

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Thanks Rick, but those beasts doesn't have removable "heads". The block is casted in 1 piece.

I'll keep you informed.

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

After changing the fuel line and primer bulb, i clean and rebuild the fuel pump and the carbs then go to a test drive.

Same thing! Go at 5000+ for 30 sec. or so then drop to 3000 rpm. But, if a manually squeeze the primer bulb, it pick up to 5000+!

So, i understand that the fuel pump don't do the job or there's a restriction somewhere, right? But the pump is freshly rebuilt and the line were new, so what can it be?

Can the compression on my cylinders been so bad (1-95, 2-115, 3-90) that there's not enough pressure to activate the fuel pump properly?

Or is there's a way to test the fuel pump?

I'm lost!

 

[akwalker]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Stupid question, but is the vent on your fuel tank open? How about changing the primer bulb and fuel line off the tank? Vacuum line to the fuel pump new? Sometimes they break down from the inside out, and collapse under vacuum, as in high speed running.

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Yeah, the vent was open, but thanks to remind!

I'll change the vacuum hose and will try to do a drive test with someone else driving at the console. Maybe with the hood removed i'll be able to see something...

 

[akwalker]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Another stupid question,,,,, is your fuel filter clean? Are you running off a portable tank? Do you have another tank? Sometimes the pickup line in the fuel tank gets clogged and impedes fuel flow. Okay, so that was 3 questions, sorry. Good luck.

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Don't be sorry, i don't think that there's stupid questions.

1 - yes, i change the merc. white plastic inline fuel filter for a generic glass inline filter with removeables cartridge.
2 - i operate from a fixed tank so it's posible that the pickup is partially clogged.
3 - yes i have a portable tank.

So, i'll first change the vacuum hose that goes from the crankcase to the fuel pump and, if it doesn't solve the problem, i'll connect the engine to the portable tank and i'll let you know what happen.

Thanks for your input!

 

[akwalker]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

1 - yes, i change the merc. white plastic inline fuel filter for a generic glass inline filter with removeables cartridge

Was this before or after the problem started? Maybe the generic filter is the restriction?

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

I change it after the problem occur, but i'll still reinstall a merc. filter. Good idea.

 

[akwalker]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Any progress with this?

 

[KARENM]

Re: Merc 1994 40 hp mariner

Re: Merc 1994 40 hp mariner

I have a 1994 Mariner 40hp outboard motor, When we turn the ignition ket it make a loud beep, even when the engine isn't going yet. When the motor starts it runs smooth and water is squirting out. Is this a serious problem or a loose wire?

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Any progress with this?

Not yet, i changed the filter for a new merc. one and replaced the vacuum hose. I'll do a drive test this week.

 

[JoeMan]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

This may or may not help at all, but I had a very similar problem this month, and JUST figured it out. My 95 Merc 60 outboard would rev all I wanted on the driveway, but in water, the r's would not get anywhere near what they should be. I did much of the same things you did, new filter, verified bulb, lines, spark, compression, etc. Then did a 24 hour carb soak. Still did not fix it. Turns out that there is that little sneaky jet at the very bottom, (I'm sure yours is the same WME 3 carbs I have) which is right next to the bottom drain screw/bolt...the largest brass screw on the carb. I took a very narrow precision screwdriver and gently applied pressure into that jet...low and behold some particles came out. I then took the largest size precision screwdriver that would fit into that jet, gently pushed through and more came out. The 1 day carb cleaner soaking did not dissolve that stuff. I rinsed it out, put back together, and my boat launched big time when I put the hammer down. Possible that you also assumed all of the jets were completely clear?

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Thanks, but i completely disassemble all the carbs (vents, jets, needles, etc) and clean them with carb cleaner and compressed air, so "i think" they were ok but maybe i forgot something.

On mine the carbs (WME 22) seems to be a bit different than yours cause there's no other opening beside the main jet brass plug, as shown here:

 

[JoeMan]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Part #19 in your diagram is what I'm talking about. It's a small jet which is directly in front of the #11 drain screw. That is what was plugged up on mine. If you've got those jets cleared out on all 3 carbs, then your problem is different. I had a hard time getting #19 out, so I left it in place, soaked for a day, rinsed many times with the cleaner. One of those had stuff built up which would not come out until I pushed it out.

The other thing I'm wondering about is your compression, since it exceeds the standard 10% difference between cylinders. Perhaps one of the pros here can chime in as to how that might play into lowered performance/rpm's.

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm

I do a lake test today :'( A bit better but not solved.

I previously reinstalled a new OEM inline filter and changed the vacuum hose (i don't use a OEM one, i change it for a piece or clear 3/16 tubing that fit snuggly on the fitting and that is stiff enough that it won't collapse under vacuum). It run at 5000+ for 1 minute or so then drop to 4500 for a few sec., up to 5000, then to 4000 etc. When i slow down to do a sharp turn or bump into waves, i then goes to 5000+ for a few sec then drop again and so on. If a pump the primer bulb, it run without problem a full rpm for a minute or so. I try with a new fuel line hooked onto a portable tank and it did exactly the same thing, so i can eliminate the line, primer and tank pickup as the source of the problem.

The only two things that i can see now are:
1- the fuel pump. I ordered another diaphragm kit to rebuild the pump again (maybe i did something wrong the first time)?
2- the bad compression that doesn't make enough pressure for the fuel pump to supply fuel at high rpms?

Any ideas?

 

[akwalker]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm... UPDATE

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm... UPDATE

I dont think your compression is low enough to effect the crankcase vacuum, which drives the fuel pump. You said that the bottom cylinder sparkplug was clean? What do you mean exactly? was it normal, tan, or was it clean as in it looked like it was new compaired to the other 2?

 

[saumon]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm... UPDATE

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm... UPDATE

You said that the bottom cylinder sparkplug was clean? What do you mean exactly? was it normal, tan, or was it clean as in it looked like it was new compaired to the other 2?

Yeah, normal tan when compared with the two others, that were oil fouled. Probably caused by the fact that there is not enough fuel pressure to supply all three carbs at high rpm. As they were fed from top to bottom, the last one will be the first to lack of fuel.

Anyway, i ordered another fuel pump rebuid kit today. I also see in my service manual that this pump should push fuel with a pressure of 4-7 psi at WOT, so is this possible to hook up a pressure gauge after the pump and check the reading at cranking speed? Does it will give something reliable?

 

[andy6374]

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm... UPDATE

Re: Merc 1993 60hp 3 cyl. wont go past 3000 rpm... UPDATE

Sounds like the fuel pump. Pumping the primer bulb effectively bypasses the fuel pump, so if pumping the bulb saves the engine then odds are it's the fuel pump.