Did I Ruin my Motor???

seth6025

Cadet
Joined
May 14, 2009
Messages
15
Ok I have a 78 80hp mercury outboard. I was driving alond fine at full power then it seemed like I lost half my power (like dropping 2 cylinders) I messed around with it and couldn't get it to come back so I started my way home on half power with the throttle full. 10 min later it kicked back in and I had full power again only to loose it in about 5 min. Now the boat has a very hard time to start and with fast idle all the way up it is hardly idleing. You throw it into gear and it just stalls because it isn't idleing high enough.
Is it toast???
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,073
Re: Did I Ruin my Motor???

You need to do a compresssion test to know if there is any engine damage. Aftyer that a spark test to see if you lost your trigger or stator.
 

seth6025

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Joined
May 14, 2009
Messages
15
Re: Did I Ruin my Motor???

so for a compression test I take out all plugs, disconnect fuel and turn it over with the tester in the top and work my way down? just checking never done it before. And spark test is just holding the plug up to the metal casing to see if its sparking?
 

green4themoney

Petty Officer 1st Class
Joined
Jul 21, 2004
Messages
318
Re: Did I Ruin my Motor???

well lets hope fuel was still being inducted into the cylinders, so in this case you would still have adequite lubrication, for your motors sake, it would be better if it was something electrical that went down, even though the parts can be a little pricey
 

d.boat

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Sep 19, 2008
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Re: Did I Ruin my Motor???

so for a compression test I take out all plugs, disconnect fuel and turn it over with the tester in the top and work my way down? just checking never done it before. And spark test is just holding the plug up to the metal casing to see if its sparking?

Here's compression testing from the johnson/evinrude forum, but I think the principles are the same regardless of brand:

1. Fully charge battery.
2. Start engine and warm her up. (of course, w/ water supply from hose!)
3. Remove all spark plugs and disconnect fuel line.
4. Rig a jumper to engage starter solenoid without turning ignition on. Pull the emergency kill switch on rope start engines. [this is to avoid frying ingnition parts, you could also remove and ground all spark plugs.]
5. Screw guage into #1.
6. Open throttle all the way. Turn engine over until reading on gauge stops increasing or 5 times, whichever is more. [i've also read that the open throttle is not necessary for 2 stroke engines]
7. Repeat #5 & #6 for all cylinders.

All psi readings should be within a 10-15% span.

* Don't get psi hysteria. Remember this is a 2 stroke engine and you are an amatuer at compression testing.
* Rope start engines will usually give lower psi readings than your know-it-all neighbor claims are required.

---------------------

As for testing spark - it should be done with an adjustable gap spark tester to determine strength of spark, not just whether it's there or not.
 
Joined
Jul 29, 2009
Messages
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Re: Did I Ruin my Motor???

I would not warm it up to check compression. You should check it cold 1st as to not do more damage. Your readings will be about 10 psi lower than if it were warm, but this will keep you from doing further damage. If all cylinders check out, then warm it up. As far as testing spark. If you have leakage from a plug wire you won't be able to see it by grounding a plug. The best thing to do would be to wait til it's dark to check for spark leakage, you can see it when it's dark, then pull the plugs and check for spark across the gap.
 

seth6025

Cadet
Joined
May 14, 2009
Messages
15
Re: Did I Ruin my Motor???

Hey just getting back to this motor issue now haha only been since last summer.....Ok I did the compression test with the motor cold and I was getting 80 psi in all four cylinders. Is that good or too low? Also I don't have one of those spark testers yet but was just wondering if there was any other way to test the trigger and stator? Also I was wondering if you have to use marine plugs or is regular ones ok?
 

seth6025

Cadet
Joined
May 14, 2009
Messages
15
Re: Did I Ruin my Motor???

It does have spark just grounding the plugs but I know that isn't telling me how good of spark.
 

Bondo

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Apr 17, 2002
Messages
71,079
Re: Did I Ruin my Motor???

Ok I did the compression test with the motor cold and I was getting 80 psi in all four cylinders. Is that good or too low?

Ayuh,... That's about 1/2 what it Should be...
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
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May 19, 2001
Messages
26,064
Re: Did I Ruin my Motor???

That is even compression and I would do a decarb..... it is a touch low but as long as it is equal you are fine.

I would imagine the rings are full of gunk and carbon.... a decarb procedure might wake that motor up. http://forums.iboats.com/showthread.php?t=158076

Use the plugs suggested by mercury
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: Did I Ruin my Motor???

On compression, don't know what you used for a gauge. Gauge could be far off. As long as it's even, it is likely OK.

Back to your problem. To troubleshoot something like this you go step by step, with the answer of each step dictating the next step. What most people don't realize about this procedure is that if you guess at the answer for a step, and you guess wrong, subsequent correct answers will only further confuse you, and theoretically you can never get to the correct answer.

OK, back to the chase. You were asked to do a compression test. That is to prove the hardware is basically sound. If it isn't, nothing you do to the ignition or fuel systems will help.

You were asked if you have adequate spark. That requires a spark tester, which is an inexpensive tool. Acquire one and perform that test, then we can logically go from there.

The plan is to check out the ignition system, because that is relatively easy and requires no parts for testing. If that is good, next you go on to the fuel system.

If you don't have a manufacturer's maintenance manual for this engine, get one. It has the procedures you need for almost any repair, as well as preventative maintenance information that will go a long way to keep you out of trouble.

hope it helps
John
 

seth6025

Cadet
Joined
May 14, 2009
Messages
15
Re: Did I Ruin my Motor???

Didn't see that last post....I will pick up the spark tester too and let you know how it goes....Thanks
 

seth6025

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Joined
May 14, 2009
Messages
15
Re: Did I Ruin my Motor???

Oh and it was a brand new compression tester I got at Canadian Tire and it said for marine use.
 
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