496 plug recommendation

Mike sandor

Active Member
Jul 28, 2017
175
Eau Claire, Wisconsin
Boat Info
2007 320 Sundancer
Twin 496. Bravo 3
2018 3500 Chevy, Loadmaster trailer
Raymarine Axiom, Quantum 2
Engines
496 Mercruiser/Bravo III drives
When I purchased my boat last year, one of the recommendations I received from the surveyor
was to replace the plugs and wires as they are original. 2007, 200 hours. I choose to run it a season just to get a baseline. I put about 60 hours on the boat last year, starts great, runs strong, (nothing to compare it to) never stalls or backfire. One thing I did notice towards the end of the season: while in gear, running maybe 1500 rpm, one motor seemed to run a bit ruff. Pulled back the other motor to idle and throttled up the offending motor and it tried to rev but just kind of labored. Felt like it was stuttering a bit. Did the same for the other motor and it rev'd smooth. I don't feel poor performance when pushing to get on plane, maybe due to the big motors but then again, I don't have any reference.
Another interesting note, just before pulling her for the season, I put in sea foam and topped off the tanks. Took one last ride to mix it up and thought, what the heck, let see what she would do as I have previously never ran wide open throttle for any duration. She came up to around 4 grand and just stayed there. After about 15 seconds, something cleared out and she took off like somebody possessed. Even the wife commented. It actually startled me and I backed her down. All gauges looked good so we went again. She jumped up on plane real quick as wasn't long and she was at 47 mph and climbing.
So, I am looking for recommendation for plugs and wires, and then she is going to the Mercruiser shop. Put her on the computer to check if there may be anything going on to be concerned about. Thoughts?
 
AC DELCO Spark Plugs: stock #41-993.
AC DELCO Spark Plug for Mercury 496/HO Engines. Replacement for Mercury # 33-863622001.

Gap @ .060 for Mercury 496/HO
 
When I purchased my boat last year, one of the recommendations I received from the surveyor
was to replace the plugs and wires as they are original. 2007, 200 hours. I choose to run it a season just to get a baseline. I put about 60 hours on the boat last year, starts great, runs strong, (nothing to compare it to) never stalls or backfire. One thing I did notice towards the end of the season: while in gear, running maybe 1500 rpm, one motor seemed to run a bit ruff. Pulled back the other motor to idle and throttled up the offending motor and it tried to rev but just kind of labored. Felt like it was stuttering a bit. Did the same for the other motor and it rev'd smooth. I don't feel poor performance when pushing to get on plane, maybe due to the big motors but then again, I don't have any reference.
Another interesting note, just before pulling her for the season, I put in sea foam and topped off the tanks. Took one last ride to mix it up and thought, what the heck, let see what she would do as I have previously never ran wide open throttle for any duration. She came up to around 4 grand and just stayed there. After about 15 seconds, something cleared out and she took off like somebody possessed. Even the wife commented. It actually startled me and I backed her down. All gauges looked good so we went again. She jumped up on plane real quick as wasn't long and she was at 47 mph and climbing.
So, I am looking for recommendation for plugs and wires, and then she is going to the Mercruiser shop. Put her on the computer to check if there may be anything going on to be concerned about. Thoughts?


check your cool fuel modules.. if the caps look like paint or (powder coating) they entire assembly needs to be changed and your injectors flushed.. this is a common issue with merc motors... i just spent close to $3500trying to fix this issue.. the modules are $1200 ish each plus shipping and labor.. then after the new modules are in flush your rails and take your injectors to get cleaned..
 
I prefer the NGK plugs for the 496
TR55IX
I used the Volvo Penta wires and they were perfect.

Agreed that cool fuel and injectors could cause your symptoms. Have that looked at.
 

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