delco MR43 plug question

[bman440440]

I have a '97 4.3 mercruiser with the occasional run on issue... the service bulletin says to go one colder on the plugs... so what is the next step colder plug than the MR43's?

 

[Fun Times]

Page 2 of that bulletin offered that info.

Available Colder Spark Plugs
Original Spark Plugs in the Engine: Short Reach Spark Plug
AC-MR43T
Replacement Colder Spark Plugs: Short Reach Spark Plug
AC-MR41T
NGK-None
Champion-RV12YC
OR Champion-RV91MC
NOTE: Quicksilver does not stock these colder spark plugs. They will have to be ordered from a spark plug distributor.

Just be sure your engine model truly uses the short reach plug as Merc just started to use the long reach plugs right around the 1997 model year too found on the Gen+ engine models.
The stickers on the flame arrestor cover may mention plug type.

 

[bman440440]

Just be sure your engine model truly uses the short reach plug as Merc just started to use the long reach plugs right around the 1997 model year too found on the Gen+ engine models.
The stickers on the flame arrestor cover may mention plug type.

my S/N 0K017681

It looks to me that I need the long plugs "816336" might you know the next colder plug from that one?

 

[Fun Times]

my S/N 0K017681

It looks to me that I need the long plugs "816336" might you know the next colder plug from that one?

I had a feeling that may be the case...Your serial number suggests you have the Gen+ engine which would use the long reach plug....That info was on page 2 as well to the right.

0K017681 = MERCRUISER TB5, W/PS, 3"RISER, (WORO,) GEN+ 4.3LX ALPHA

Original Long Reach Spark Plug AC-MR43LTS.
Replacement Colder Spark Plugs For Long Reach Spark Plug:
AC-None
NGK-TR6
Champion-RS9YC

SPARK PLUG (#33-816336Q)
Supersedes: 33-816336, 33-834988 13, 33-854278
https://www.perfprotech.com/mercury-marine-parts-catalog/umodel/16506