I have a 1978 Mercury V-1500, 150 hp V6. I have been gradually tuning and repairing it until it's running pretty strong-- head gaskets, seals, thermostats, carb and fuel pump rebuilds. Pretty much normal stuff for one this old.
Toward the end of this season, it has had some misfire at speed, which I attribute to its 3-year-old spark plugs. It also still has the factory original spark plug wires and coils. The coils test within specs, so I'm assuming they are fine. The plug wires are wire-core, but the boots are getting tired, so I'm going to replace the plug wires along with the plugs.
When I replaced these plugs 3 seasons back, I could only find them in NGK (BU8H). Now they are available from NGK and Autolite (2852). Most manufacturers have discontinued these plugs. These are a "surface gap" or "semi surface discharge gap" design. Typical of my experience with NGK spark plugs (it hasn't been happy), they lasted 3 seasons, but they don't have very many hours, maybe 15 or 20 hours total, and they are misfiring already.
This motor is now over 30 years old. Surface gap plugs are designed to prevent fouling by allowing the spark to travel over the surface of the insulator, at the cost of less efficient fuel/air burn.
Spark plugs and 2-stroke oils have advanced a lot in 30 years. I only run full synthetic oil, which wasn't available when this motor was new. That alone greatly reduces the possibility of fouling.
Is there another type of spark plug that would work better? When I replaced the head gaskets, I could see that there is plenty of clearance for a more conventional protruding nose spark plug, with flat-top pistons and hemi-shaped heads. Fine wire precious metal electrodes and improved heat control prevent fouling nowadays, with much better ignition.
Can anybody tell me if there is good reason not to try a more modern spark plug?
(Added info)-- As an example, I also have a 2-stroke Polaris ATV, water-cooled. I use the same synthetic oil in it as I use in the outboard. Spark plug applications for the Polaris list both conventional and surface gap plugs. The major difference between them is that the conventional plugs are 4 heat ranges colder, which makes sense.
Toward the end of this season, it has had some misfire at speed, which I attribute to its 3-year-old spark plugs. It also still has the factory original spark plug wires and coils. The coils test within specs, so I'm assuming they are fine. The plug wires are wire-core, but the boots are getting tired, so I'm going to replace the plug wires along with the plugs.
When I replaced these plugs 3 seasons back, I could only find them in NGK (BU8H). Now they are available from NGK and Autolite (2852). Most manufacturers have discontinued these plugs. These are a "surface gap" or "semi surface discharge gap" design. Typical of my experience with NGK spark plugs (it hasn't been happy), they lasted 3 seasons, but they don't have very many hours, maybe 15 or 20 hours total, and they are misfiring already.
This motor is now over 30 years old. Surface gap plugs are designed to prevent fouling by allowing the spark to travel over the surface of the insulator, at the cost of less efficient fuel/air burn.
Spark plugs and 2-stroke oils have advanced a lot in 30 years. I only run full synthetic oil, which wasn't available when this motor was new. That alone greatly reduces the possibility of fouling.
Is there another type of spark plug that would work better? When I replaced the head gaskets, I could see that there is plenty of clearance for a more conventional protruding nose spark plug, with flat-top pistons and hemi-shaped heads. Fine wire precious metal electrodes and improved heat control prevent fouling nowadays, with much better ignition.
Can anybody tell me if there is good reason not to try a more modern spark plug?
(Added info)-- As an example, I also have a 2-stroke Polaris ATV, water-cooled. I use the same synthetic oil in it as I use in the outboard. Spark plug applications for the Polaris list both conventional and surface gap plugs. The major difference between them is that the conventional plugs are 4 heat ranges colder, which makes sense.
