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1999 Johnson 70 hp loses a Cyl under load

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larrypickett

New member
1999 Johnson 70 hp 3 cyl,I have a problem I have been working on for 3 years. After say 20 minutes under load, I lose a cylinder. I have replaced, plugs, wires, coils, power pack and stator... I have also rebuilt the carbs, All to no avail. This is rather discouraging. I have tried an axillary gas tank to rule out water in my gas....
On my I/O there is a switch that takes out 1 or two cylinders is there the same technique on my outboard and secondly HELP!
Larry
 
u need to determine,if u r losing--ignition,compression ,or fuel....i would guess,if no mechanical prob's,..u r overheating and going into SLOW,or ...u have a bad pack,or sender,throwing u into SLOW,needlessly....disc temp senders and try.
 
I am getting plenty of water through the water pump, indicated by a good stream leaving the exit tube. Can a faulty temperature sensor cause this issue? and how?
 
When this problem surfaces, check the compression and make note of the readings and let us know what they are. Then with the spark plugs still removed, check the spark which should be jumping a 7/16" gap on all cylinders..... let us know what you observe.

Do all the the spark plugs look the same or is there a difference? What do they look like..... if a difference, which cylinder?

Even if all of the above checks out to be normal, the possibility exists that an extremely slight defect exists with either the head gasket or the sealing surfaces of the head/block. If so, this would, especially after the engine reached operating temperature, allow a fine spray of water to enter a cylinder which would obviously kill the cylinder....... this condition normally also creates a pre-igniton condition which will cause piston damage if not corrected with a short time.

Water could also enter via a faulty exhaust baffle cover gasket or sealing area BUT the head gasket is the most likely area for this to happen.

Let us know what you find.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
 
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