50 hp johnson, smashed spark plug, and power loss

M

mwbaughan

Seaman Apprentice
Joined
Nov 14, 2002
Messages
47
1975 2cyl- finally got running good, and then started loosing rpm like starving for fuel.<br />I put a fuel pump on and carbs were recently rebuilt. After high rpm take off, looses power and then will not restart until next time completely cold. Second time I found tip of spark plug pressed against electrode and looks like it has been beaded by high temp explosion in cylinder. No hole in piston though. Could <br />this be a coil problem on that cylinder?
 
O

ob

Admiral
Joined
Aug 16, 2002
Messages
6,992
Re: 50 hp johnson, smashed spark plug, and power loss

bodyman,What plugs are you using?Sounds like you've got some mechanical interference between piston and sparkplug.
 
H

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: 50 hp johnson, smashed spark plug, and power loss

That's what it sounds like to me but I'd be concerned about the metal beading on the plug too.<br /><br />c/6<br /><br />Hooty
 
O

ob

Admiral
Joined
Aug 16, 2002
Messages
6,992
Re: 50 hp johnson, smashed spark plug, and power loss

bodyman,I would recommend performing a compression test and a spark test to begin problem search.
 
B

Bob in Calif.

Senior Chief Petty Officer
Joined
Nov 4, 2002
Messages
653
Re: 50 hp johnson, smashed spark plug, and power loss

If you use Champion plugs, you should be using #QL77JC4 or new stock number of 828, with a .030 gap. .......Bob in Calif.....
 
W

wakataka

Seaman Apprentice
Joined
Aug 23, 2002
Messages
47
Re: 50 hp johnson, smashed spark plug, and power loss

Bodyman - <br />Sounds like you have a piston with broken rings that is seizing against the bore walls when you run it hard. The broken pieces of the ring can work their way up to the top of the piston and smash the plug gap shut. If you're using the right plugs, you can't have that happen unless there is something in the combustion chamber. A compression test could tell a lot.
 
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