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4.3 Mercruiser backfire

A

ASD

New member
if there might be anything else I could try to fix the back fire through the carb from cylinder #6.


4.3 175 HP MERCURY CRUISER 6 CYLINDER

In the fall and early spring no problems. My mechanic informed me that the starboard side manifold needed to be replaced(original and it should be replaced 5-7 years) which I did and once it was replaced, I have been having a popping noise (back fire )from cylinder #6only.Performed pressure and leak down test with good results. I can run boat with out the wire on the cylinder and it will not back fire. I have already replaced wires and cap in hopes it might be that.
When running boat in gear at 2800 -3000 rpms popping will happen sporadically. sometimes it stops for about 30 -45 seconds. I have not pushed engine in fear of blowing rod.

we have removed both heads and found no problems (well starboard had an exhaust rod that was mushroomed) when we had them tested. We have check carb, rotor cap wires, gas ect. and performed all tests.

any other things it might be? (TIMING CHAIN?)


Thank you in advance for your help.
 
It sounds like it is spark related. Did you use quality replacement wires? Are the wires crossed anywhere along their runs? Look carefully at the under side of the cap for carbon tracking to/from the #6 spark tower. Look carefully at wires 2, 4 and 6 for carbon marks on the innsulation.
 
Flat Cam?

(well starboard had an exhaust rod that was mushroomed) I dont know what this is but it can't be good. If you have a valve that is bad and it does not open it will pop!
 
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