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Author Topic:   Engine Diagnosis: 1985 OMC 150-HP
tlynch posted 08-17-2002 07:50 PM ET (US)   Profile for tlynch   Send Email to tlynch  
Well, I own a 1985 Johnson 150 HP, It was running perfectly all summer until the past two weekends.

Now if I put it in neutral it idles around 500 RPM and then dies and when I give it gas it slowly works its way up to a plane but never gets above 4800 RPMS, WOT is usually 5800. The power slightly surges at some points but never too much.

I premix 50:1, Injection has been disconnected.

I replaced the fuel lines, fuel vent hose, and water separator this past winter. I just replaced the plugs and plug wires and thermostats.

When I replaced the plugs (NGK) the top one in each bank was pretty black. I had never replaced the plugs - I bought the boat a year ago.

Pumping the bulb does not seem to help, it is a new OMC bulb.

I think that I will replace the fuel filter and clean out the water separator tomorrow morning.

Any suggestions will help.

Thanks a million,
Todd Lynch

raygun posted 08-17-2002 09:07 PM ET (US)     Profile for raygun  Send Email to raygun     
check the coil connections for corrosion.
JohnAz posted 08-17-2002 09:42 PM ET (US)     Profile for JohnAz  Send Email to JohnAz     
chack the throttle linkage ....remove air filter and look at the location of the throttle plates,,one of my 40 had shifted, even though everything was tight
vdbgroup posted 08-17-2002 10:18 PM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
Time to replace stator.
jimh posted 08-17-2002 10:41 PM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "My engine needs a kick in the..."--jimh.]
Al_A_Buy posted 08-19-2002 09:38 AM ET (US)     Profile for Al_A_Buy  Send Email to Al_A_Buy     
vdbgroup - What do you mean "time to replace the stator"?

tlynch - Similar problem on my 1985 185 Johnson. Thought it was just oldage setting in until the motor quit running while fishing with my boss. He had to stand in the motorwell and squeeze the bulb all the way back to the dock. Can you say career limiting? :-)

Turned out to be the VRO/fuel pump had been cracked for awhile and finally gave up the ghost. The surging was due to air being sucked in thru the crack.

Check the pump by squeezing the bulb and looking for gas leaks.


Hank posted 08-19-2002 09:32 PM ET (US)     Profile for Hank  Send Email to Hank     
Check for leaks at VRO as suggested by
AL_A_Buy. My '84 Evinrude 90HP just developed a bad leak at the VRO/pump unit. Mine is so bad I won't attempt to start the engine until it is repaired.

It's easy enough to do. Squeeze the bulb hard. Look and feel around the VRO unit.

I presume you replaced your VRO unit. I am looking for a less costly alternative since I premix. (see my post in Repair section)


Dunk posted 08-21-2002 08:56 PM ET (US)     Profile for Dunk  Send Email to Dunk     
One possibility is a bad coil on that cylinder. Pull that plug wire then go for a ride. If she feels the same at least you know where the problem is. That one black plug is sure indicator it's not firing. New coil about 30 bucks. You can try swapping coils around and see if the problem follows that coil.

Has anyone checked the compression?? Too often when they won't idle and don't come up to rpm's it's broken rings, scored cylinder walls.

swede5 posted 08-22-2002 09:47 PM ET (US)     Profile for swede5  Send Email to swede5     
I agree with Dunk. My 1987 225 Johnson had similiar symptoms 3 weeks ago. I lost about 500 rpms. I bought a spark tester and learned that one coil was history and one was sporadic. Two new coils and I am back in business.
jimh posted 08-22-2002 11:56 PM ET (US)     Profile for jimh  Send Email to jimh     
Where did you get the spark tester?

It sounds like a handy gadget to have.

george nagy posted 08-23-2002 12:18 PM ET (US)     Profile for george nagy  Send Email to george nagy     
You can use an ordinary timing light to tell if a plug is firing. If it is a coil I have a brand new bombardier made coil for an 87 150 if you need it let me know.
tlynch posted 08-25-2002 10:05 PM ET (US)     Profile for tlynch  Send Email to tlynch     
OK. I took it to a shade tree mechanic and the news was not good.

He took a look at the spark plugs and saw that there was water in the top two cylinders on the starboard side. The compression on the other 4 was 90. He took off the head and found that the outside of the cylinder wall was being corroded by salt, and water was leaking in through the head gasket.

Originally the cylinder wall was approx. 8mm thick, now in some places, the wall is only half that thickness. There might be two corroded places per cylinder. The wall was eaten away from the outside towards the inside and each place was roughly along 7mm of the circumference of the cylinder.

He recommended cleaning everything up and putting it back together, that there was not much else that could be done.

Any thoughts on how long this might last? It stinks to have an engine that could blow out at any time. It would be great to put off buying an engine for a couple of years.

If you keep your boat on a mooring how can you flush the engine?


WSTEFFENS posted 08-26-2002 04:17 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     
The spark testeter probibly was a unit refered to in an OMC shop manual. I made one from a large (8 1/2 x 11 x 1/2m thick) slab of industrial formica. This because of its teriffic electrical insulation capability. To this base were installed moveable (adjustable) gap plates made of brass using spindle nuts for hold downs and old spark plug pins to attach the plug wires. The purpose was to check the max gap or ideal gap stated in the manual to check coil and stator coil (the stator coils fire the power packs or coils) performance. You would install this unit and while at idle you could see if any of the jugs had weak spark. Obviously this was in the driveway with water "earmuffs" on.


SWarren posted 08-27-2002 10:57 AM ET (US)     Profile for SWarren  Send Email to SWarren     
Water in the cylinder is not that bad if caught early which you probably did. You can get a new cylinder head for probably 175 dollars and the head gaskets are cheap. You will probably have some corrosion on top of your piston, but of the walls are not scored are corroded and the compression is still good, a new cylinder head should last you a while. I hear this is fairly common on omc motors but it happens mostly on the bottom cylinders mostly the left one.
tlynch posted 08-27-2002 01:05 PM ET (US)     Profile for tlynch  Send Email to tlynch     
Luckily the inside of the cylinder and piston looked nearly perfect, no corrosion and no scoring. The cylinder head also appears to be in decent shape now that it has been cleaned up. Unfortunately the worst of the corrosion was on the engine block side of the cylinders, on the outside of each cylinder.

The cylinder wall has corroded to about half of its original thickness in some places around the rim or the cylinder. We are afraid that a good seal will not be made with the cylinder head as this seam is where the corrosion took place.

Thanks for your input,

Bigshot posted 08-27-2002 02:59 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Should be good for a while....maybe years. With a 198, you got your money worth. Try to repair and run till she blows. Start saving your money but at least it won't leave you stranded. She'll run fine on 5 cyls, long enough to get in, etc. If you check your plugs regularly and see that 1 or 2 are REALY clean, she is starting to ingest water which in small doses, clean your plugs real nice.
tlynch posted 08-27-2002 04:07 PM ET (US)     Profile for tlynch  Send Email to tlynch     
Thanks Bigshot - I was waiting to hear what you had to say.


Bigshot posted 08-27-2002 06:00 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Got nothing to lose except a couple hundred bucks. If I can get a month out of it I would be happy. You might get a couple years.
Bigshot posted 08-27-2002 06:03 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
What "I" would do is get some JB weld and build up the wall where it is eaten away if it is bad. Without seeing it would be hard to tell. The JB is a patch but that patch will outlast the rest of the water jacket. remember this is only the water jacket we are talking about. If it was something that was under stress or could cause danger I would never suggest it. All you want to do is keep the block from rotting away. If it took 17 years to get where it is at now, some JB weld and some sanding filing to make level should last another 17.
tlynch posted 09-02-2002 07:44 PM ET (US)     Profile for tlynch  Send Email to tlynch     
I got it back this weekend.

After we fixed the compression problem it turned out that there were also two bad coils.

Now runs fine.

Thanks for all of you help.


Dunk posted 09-02-2002 09:53 PM ET (US)     Profile for Dunk  Send Email to Dunk     
Very unusual to see an OMC water jacket corroding away like that. It must have been a casting flaw when it was built.

Actually most of the sealing between the head and block is done on top of the steel cylinder sleeve. All those cylinders have steel sleeves in them. As long as the head was flat and not warpped which can cause the problem you are seeing she should run for awhile. When the gasket is not held/clamped tight it will pulse with piston going up and down. The gasket moving can actually destroy the alum surface there and leave it suseptable(sp) to corroding.

I would have felt better hearing you had that head sent out to be decked before it was reinstalled. Decking is just removing .0010 of material just to clean it up and make sure it's flat for good seal.

One thing you want to make sure you do is...after 15-20hrs running get that head retorqued. Your mech should have mentioned this....It's SOP on any head gasket replacement..

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