2000 Johnson 70 HP #3 cylinder problem

yorkeken

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Joined
May 17, 2003
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3
Mid December, 2002 (salt water temp approx 48 degrees F.)<br /><br />Out for ride. Running approx. ¾ throttle.<br />Engine suddenly lost power and could not maintain plane. Limped home.<br /><br />May, 2003<br /><br />New plugs installed<br />Test ride – ran ok. until motor fully warmed up. Lost power again.<br />Checked fuel mixture per service manual - checks out ok.<br /><br />Problem is in the #3 cylinder. I tested all of the cylinders individually by pulling off the other two plug wires. #1&2 ran ok and #3 runs but is intermittent and misses.<br /><br />Did as much diagnostics as I am capable of doing without special testing equipment. They are as follows;<br /><br />1. Switched spark plugs to rule out defective plug - no change<br />2. Switched ignition coil with #1 cylinder to determine if the coil was bad - no change<br /><br />This problem is definately related to a fully warmed up motor and is only affecting the #3 cylinder.<br /><br />Could it be the power pack? Is it something that can go like that and only affect 1 cylinder?<br /><br />Any suggestions as to what else it might be?<br /><br />Thanks in advance for any and all replies.<br /><br />Note: When brand new, the engine (once at operating temp) would stall if turned off for a short time when re-started and put into gear. The problem was reduced once I richened the fuel mix by adjusting the needle screws and had no problem for 2 seasons.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: 2000 Johnson 70 HP #3 cylinder problem

Howdy, Yorkeken.<br /><br />Temperature related intermittent failures are usually electronic. In your case, the powerpack.<br /><br />I think you have enough evidence to swap it, but I also believe in proving a part is bad before spending big bux to replace it.<br /><br />As I understand you, the #3 cylinder makes power when cold or cool, but when the engine warms up it begins to fail.<br /><br />Electronics troubleshooters use two tricks to help isolate temperature related failures: hair dryer (heat gun) or chilling spray. The spray is available at Radio Shack or similar outlets.<br /><br />Heat the powerpack up when the engine is cold and see if it fails quickly, then chill it when the engine is warm and see if it begins to work again.<br /><br />Good luck, and let us know what you find. :)
 
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