Changed the sparkplugs on my '87 Merc 454 and now idles at 800 rpms instead of 650.

[supersizeme]

I changed my spark plugs and it now idles kinda high. I see in the Mercruiser manual it's only supposed to be 650-750 so what should I look for?

 

[TowRoper]

Re: Changed the sparkplugs on my '87 Merc 454 and now idles at 800 rpms instead of 65

i guess start at the obvious and ask are they the proper plugs and adjust the idle screw on the carb?

 

[myoldboat2]

Re: Changed the sparkplugs on my '87 Merc 454 and now idles at 800 rpms instead of 65

what condition were the old spark plugs in?

what model spark plug were the old ones? new ones?

what engine? year?

 

[Don S]

Re: Changed the sparkplugs on my '87 Merc 454 and now idles at 800 rpms instead of 65

IF you used the proper spark plugs, I would say you were WAY overdue for a tuneup. Might want to have a look at the cap and rotor while your at it. After all is checked and replaced, adjust the carb idle down to specs, check the static timing and advance timing. Make sure the idle mixture is set correctly, along with idle speed and go boating.