Bad spark knock....help

[k-dog]

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.

 

[maxxman04]

Re: Bad spark knock....help

spark knock usually indicates a lean condition, or as you have checked, a timing issue. seems like timing might be ok, so check the carb. or possibly vacuum leak. sounds like one way or another, there is too much air getting into motor.

 

[JustJason]

Re: Bad spark knock....help

So why did the port motor originally blow??? and why is it on the verge of blowing again.... Somehow I bet the 2 are related....

 

[Bondo]

Re: Bad spark knock....help

Ayuh,.... Sounds like a Fuel Delivery Issue hasn't been dealt with yet...

 

[k-dog]

Re: Bad spark knock....help

Thank you for all of your suggestions I will look into them all.

The first motor failure was unrelated to this issue, it simply just dropped a valve.

I will check for vaccum leaks.

After I switch the distributors the carbs were going to be next... that should answer that question.

Again thank you!!