From The Forums-Spark Plugs

Published in the September 2008 Issue September 2008

What would you do without spark plugs? They're such a small, relatively inexpensive object not much bigger than a dart, and yet without them-or at the very least, with one that's corroded-the increasingly expensive gasoline you put in the fuel tank would be worthless. Even a corroded spark plug will turn a powerful boat into something a paddle boat could probably lap. Truly, spark plugs are worth their weight in gold.

Recently, a Senior Member asked his fellow PDB comrades a question regarding how often he should replace the small and simple firing devices in his boat engine. They responded appropriately, with one Senior Member even going so far as to state the exact product number of the spark plug that was needed.

Paulangelo asked: Just wondering: how often do you change your spark plugs? I have a two-stroke Mercury 90 EFI (wish I had an Optimax). Had it for three years and never changed them out. Now it seems to run a little rough and has stalled out after being out all day and coming into the slip. Not a good feeling when you are between all those boats and have no power. I have to call the dealer on the best plug and gapping so this weekend I can change them out. Anyone know what the three-cylinder, 90 EFI takes? I am hoping this fixes my "issue."

rickdb1 responded: I change mine every spring. Three years is pretty good for a two-stroker. The correct plug is NGK# BUZHW-2. These are surface gap plugs, so there is no gap to set.

HEATMAN agreed: I change mine every spring right after I burn off the fogging oil from winterizing. Mine only run about $2.50 each and it takes maybe five minutes.

krober asked: Rick, are those surface gap plugs available for other applications? Mine has the conventional plugs, but I think the surface gap plugs would last longer in a two-stroker if I could find the correct ones for my application.

rickdb1 replied: I don't see a recommended alternative for your engine. The NGK# BPZ8H-N-10 is the only correct plug they show.

Paulangelo returned: Rick, thanks. I picked them up tonight and am going to install them this weekend. From the looks of them, they HAVE to help in the performance with my motor. I believe I have Champions in there now. Three years old is right-never changed them since we've had the boat. So, if it is running okay now, new plugs should really help-and with GPH too, right?

rickdb1 answered: I would think they'd have to help, Paul. Sure, it couldn't hurt. You got your money's worth out of the old ones, I'd say....

Five days later, Paulangelo reported in with an update: Well, I just got to say, 10 minutes of work (and still in the water at the slip) and got all three plugs changed. What a difference!! I should have done it before launching, but the plugs never entered my mind. I thought the dealer was changing them when they winterized, but now I understand why they shouldn't do it then! Took some shots of the new and old plugs. Will upload them tonight if I get the chance. Have a few different things to upload on my list of next year's to-do. Changing the plugs is there.

jimrs said: On surface gap plugs, I have gone three years without any problems. But on regular plugs, one year and then I change them. I am starting on the second year on my current plugs. If it starts missing, I will change them.

dcm8063 chimed in with a new question: Question for the experts: I too have a 90hp Mercury two-stroke, Pro Series EFI. I pulled the top plug of the three last night, and it is an NGK BUHW-2. rickdb1, you told Paulangelo that the correct plug is an NGK# BUZHW-2. I'm confused. Which plug should I use?

VoyagerV20 answered: I think they're the same plug. The BUZHW-2 is a resister plug (supposed to not bother electronics, radio), where the BUHW-2 is a no-resister.

To read this thread in its entirety, please visit the forum page at and search for the "spark plugs" thread.

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