mercruiser 470 back firing

C

CHLOEMAX25

Recruit
Joined
Jun 19, 2008
Messages
2
I have 2 mercruiser 470's 1984 170hp 1 of the engine backfires out the carby i have change all the fuel filters, it dose it about 30-60 min in to the trip, back fires 2 or 3 times then it want do any thing for for a few minutes and then it will do it again, the tacho gose crazy before and after it happens and wile it is back firing and i know the tacho runs of the coil i am not sure if this is the problem any help would be good
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: mercruiser 470 back firing

You could be getting cross fire from a cracked distributor cap, bad plug wires, or a cracked coil tower arching to the tach terminal. Cracked coil towers are often caused by bad wires.
 
J

jayrodoh

Seaman
Joined
May 12, 2008
Messages
70
Re: mercruiser 470 back firing

I agree with Don, especially if the tach is acting up, that would point directly at an ignition problem.
 
R

RJLeuwen

Seaman
Joined
Jun 19, 2008
Messages
69
Re: mercruiser 470 back firing

Try disconnecting the Tach lead at the coil (gray wire on the - neg. side of coil) and run it that way for the same amount of time If no backfire Replace the Tach. If backfire persists cuold be a bad resistor wire in the engine hariness.

RJ
 
C

CHLOEMAX25

Recruit
Joined
Jun 19, 2008
Messages
2
Re: mercruiser 470 back firing

thanks heaps i will try some of these and see what happens
 
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