spark plug recomendations?

'75 merc 1150 inline 6 needs to be changed and I am looking for opinions. Should I stick with surface gap or switch to the conventional type which Ive read are hotter burning?
any help is appreciated

Re: spark plug recomendations?

Surface gap plugs are designed and spec'd primarily for sustained high speed running. Some owners that extensively troll at or near idle have changed to a standard electrode gapped spark plug such as the NGK B8HS or B7HS which is very near the same heat range.

Prior to any change in plug design check spark plug to piston clearance to ensure at least .080 between the tip of the ground strap and the piston.

Some motors have sufficient clearance to run an extended tip plug such as the NGK BP8HS.

If you are having problems with plug fouling it may not necessarily be the spark plug causing the problem. Carb cleanliness, float level adjustment, leaky needle/seat, can over fuel and prematurely foul/kill a set of plugs.

Are you having a problem, and if so, what have you checked, or done so far?

Re: spark plug recomendations?

The slow trolling might explain my issue (Lot of idle speed zones and scanning for scallops during season.) being the #5&6 plugs tend to get a lil fouled but not enough to cause it not to run,it just bogs a bit when taking her up on plane and then she is fine after that.

Re: spark plug recomendations?

That motor has Direct Charge combustion chambers and a regular tip plug would be struck by the piston. Try using a synthetic oil like Amsoil, it burns cleaner and can be run at mixes up to 100:1. My '75 850 runs clean without a lot of smoke.