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Gapless plugs on my 1998 200 HP is there a reason Is this the plug to use

S

sbklf

Contributing Member
"I just purchased this boat/motor (1998 200 HP Merc carbeurated) and it has those plugs in it that are flat on the end less the little arm over the electrode. When I saw them it came to mind that the previous owner might have installed them to overcome a fouling issue maybe?

I will change the plugs, is this the style plug that this motor uses?

I ran it yesterday and it ran OK wide open throttle but idled a little rough with an occasional backfire."
 
"Kevin, Merc does call for a &

"Kevin, Merc does call for a "surface gap" plug on that model - an NGK BU8H to be exact (and you really should run nothing but NGK's - the resistance of some other plugs doesn't work so well with Merc's which were engineered for the NGK's).

Sometimes there will be a "gapped" option as well, but not for your particular model.

Surface gap plugs are most often recommended for "sustained high speed" operations with regular gapped plugs (better) for lower speed (trolling etc).

Unfortunately there is nothing (kinda in the middle).

Since you have just picked up this rig I would change the plugs and run a can of Merc's "PowerTune" through it (about 5 bucks a can) which will clean out the carbon and other "cooties".

Also, unless you have seen receipts to prove maint was done, I would change the impeller and lower unit oil just to be safe...."
 
"Thanks for the replies. I cha

"Thanks for the replies. I changed the water pump already and will change the plugs. I will also pick up some of the "Power tune", thanks for the tip."
 
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