Bad spark knock....help

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k-dog

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Jul 11, 2009
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I have a 1995, 29 foot Scarab with twin Mercruisers 350 mags., the port side motor blew and i rebuilt it. After a break-in period and a few more runs it suddenly developed a bad spark knock. I have turned the timing all around and can't get it out. I switched the knock sensor and the knock module with the other engine but it didn't follow the motor.

Any suggestions.

I was wondering if it could even be mechanical like jumped valve timing or something. I don't mind pulling the motor but want to know the problem is inside bofore I do.

Please help.
 

towman818181

Seaman Apprentice
Joined
Aug 31, 2008
Messages
44
Re: Bad spark knock....help

chk timing with a light and see your total advance and whats the temp on that motor running is it running lean may have a piece of carbon on one of the pistons
 
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