1987 Evinrude 120 Running Rough

[LukeWilson]

Heys guys, new here and fairly new to boating but I'm fairly mechanical. Just finished doing the floor and transom in an '87 Checkmate Predictor and now i'm having some issues with the motor.

At first it would run fine at low rpm, but would bog out at higher rpm after 15 seconds. I pulled the carbs apart (which appeared very clean), stuck them in the ultrasonic and replaced the primer bulb. It ran much better but i was still only getting 40mph and slow to get up on plane. I found that the spark advance was being restricted by a cable holding bracket today and took care of that issue. I went out and it really helped, boat popped out of the water great and really seemed to scream along. Then it shut of on me, it came to a pretty quick hard stop. Eventually i did get it going again but it has a really rough bag or rocks sound to it and i'm afraid im doing some kind of damage.

Water outlet seemed slightly less after the shut down, before it was a fairly hard jet and now it is only a constant stream. Compression test was 125 across the board before and after i had it going. I also appear to have very good spark on all the cylinders. Nice little cloud of smoke on start up leads me to believe it's getting oil.

Any thoughts?

Thanks guys,

Luke

 

[kenmyfam]

Re: 1987 Evinrude 120 Running Rough

Heys guys, new here and fairly new to boating but I'm fairly mechanical. Just finished doing the floor and transom in an '87 Checkmate Predictor and now i'm having some issues with the motor.

At first it would run fine at low rpm, but would bog out at higher rpm after 15 seconds. I pulled the carbs apart (which appeared very clean), stuck them in the ultrasonic and replaced the primer bulb. It ran much better but i was still only getting 40mph and slow to get up on plane. I found that the spark advance was being restricted by a cable holding bracket today and took care of that issue. I went out and it really helped, boat popped out of the water great and really seemed to scream along. Then it shut of on me, it came to a pretty quick hard stop. Eventually i did get it going again but it has a really rough bag or rocks sound to it and i'm afraid im doing some kind of damage.

Water outlet seemed slightly less after the shut down, before it was a fairly hard jet and now it is only a constant stream. Compression test was 125 across the board before and after i had it going. I also appear to have very good spark on all the cylinders. Nice little cloud of smoke on start up leads me to believe it's getting oil.

Any thoughts?

Thanks guys,

Luke

But is it getting enough cooling ???
Basic health check to begin with.
Compression
Spark
Fuel delivery
Spark plug condition
If you don't know when the impeller was last changed then it is due if not too late now ??
Is the VRO/OMS pump being used ???
Does it have any oil in it ??
Is the fuel bulb collapsed ??
Couple of links to check out.

http://forums.iboats.com/showthread.php?t=309188

http://forums.iboats.com/showthread.php?t=400771&highlight=impeller+kenmyfam

Lots more stuff but I have to get to work.
Welcome to iboats

 

[LukeWilson]

Re: 1987 Evinrude 120 Running Rough

I recently bought the boat so i have no idea on when the impeller was last changed, there is certainly water going through it though. I went less than a km on the water when this happened after idling for half a km and the block didn't seem excessively hot.

Compression was 130 psi across the cylinders before it was in the water and 125 after, only 1 or 2 psi variation.

Very strong spark, i cleaned the plugs they were all a chocolate brown color under the the black oil.

Starts fine even after the incident, no reason to believe there is a fuel shortage.

I am using the VRO, lots of smoke on start up and i do notice it while it is running. I added a couple liters of shell nautaulis a few days ago.

Fuel primer can be pumped until hard, not collapsed when it was running.


Is it possible to have taken out the crank bearings if it overheated? Something just doesn't sound right when it's running.

What is the easiest way to check if it is running on all cylinders?



Thanks,

Luke

 

[jtexas]

Re: 1987 Evinrude 120 Running Rough

Cylinder drop test:
With engine idling pull, then replace, the plug leads (one at a time), give the motor a second to respond. If the cylinder is making power, RPMs will drop noticeably. (Use a plastic or insulated tool to avoid a nasty shock. Or get some help from somebody you don't like too much.)

Consistent 5 PSI drop on all cylinders suggests a variance in test procedure -- different tester, warm/cold engine, open/closed throttle, spark plugs in or out, battery less than full charge, yada yada yada?

For me, any noticeable decline in water pressure out the telltale always prompts an impeller change. You can inspect and reinstall if it's ok, I always just replace it regardless to save on labor (my own labor of course).

If you added synth to regular oil (or for that matter, mixed different synthetics), you might want to check the condition of the oil in the reservoir.

Somebody who knows better than me will have to address your crank bearing question.......

 

[LukeWilson]

Re: 1987 Evinrude 120 Running Rough

I think i am going to start with an impeller change and have a look in the cylinders with a borescope for scoring. I talked with someone very helpful at aim outboard recyclers (in Ottawa) who seemed to think i might have been a hot seizure given the vague description. I'm going to compression test it again tonight as it will be dead cold and see what it shows, i might have cooked the rings.

Thanks guys,

Luke

 

[archcycle]

Re: 1987 Evinrude 120 Running Rough

You should actually compression test it warmed up.

 

[LukeWilson]

Re: 1987 Evinrude 120 Running Rough

Update:

Did a leak down test which failed horribly and then pulled the heads tonight and found the problem. It did overheat and seize the top left piston (opposite to the water pisser) because the impeller shredded and plugged up the thermostat. The bores to near perfect, can still see cross hatching in all of them. I cleaned up the little bit of smeared aluminum with some muriatic acid and i plan on pulling it down and putting new rings in it. I am a little bit relieved to find an obvious problem because i would hate to put it back together and have the same thing happen. So the moral of the story is replace your impeller the second you buy the motor!!!!


Thanks for the help,

Luke

 

[Fed]

Re: 1987 Evinrude 120 Running Rough

You might want to check the temp alarm is working too.

 

[kenmyfam]

Re: 1987 Evinrude 120 Running Rough

Update:

\ So the moral of the story is replace your impeller the second you buy the motor!!!!


Thanks for the help,

Luke

Absolutely !!!
Good luck with the repair

 

[jtexas]

Re: 1987 Evinrude 120 Running Rough

you have a borescope! How bout moving in next door to me?