Correct Spark Plug for Mercury 900 Inline 6 (90hp)

K

kmk89

Seaman
Joined
Jan 30, 2009
Messages
55
I have a 1978 Mercury 900 (90hp) inline 6. I just got it and wanted to replace the spark plugs on it. The current spark plugs in the engine are NGK plugs Part No BUZHW, which I believe are the resistor type spark plugs. I just want to confirm that you can use these resistor type spark plugs on engines with the Thunderbolt Ignition. I remember reading somewhere that you shouldn't use the resistor type spark plugs. Should I go with NGK BUHW plugs instead (non resistor type)?
 
E

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: Correct Spark Plug for Mercury 900 Inline 6 (90hp)

The Stone-Age Capacitance-Discharge-type ignition on your 90hp Tower of Power probably doesn't care about using that type of plug with a built-in inductive resistance. They are quite expensive, compared to the standard Champion L-76V, Autolite 2852, AC V40FFM, NGK BUHW, etc.

Merc has been using the "Z" plug on newer motors with sensitive electronics, but the ign on your Merc is a late-60's design and quite unsophisticated.

If the BUZHW plugs are in decent shape, you could just clean them & reinstall. Surface-gap plugs usually have a very long life unless they are badly fouled, or the center electrode gets worn down.

If you have a NAPA nearby, they can get the above-listed marine plugs a lot cheaper than a Merc dealer or most marine stores.

Here's a thought, if you do pick up a set of the non-resistor plugs, see how they compare to the "Z" plugs. You may find that the motor starts & idles a bit better with the "Z" (according to some postings I've seen).

But more than likely there won't be much diff except a lighter drain on your pocketbook!

HTH & let us know what happens..........ed
 
You must log in or register to reply here.
Top