Real life test: "Selva 50HP Madeira 684cc MAGNUM Boat Performance Spark Plugs"

According to Selva Marine you should use Champion L78 or Bosch W3AC spark plugs with Selva Madeira 40 XS. The 50 HP model uses the same plugs. Some matching spark plugs from other manufacturers are:

• NGK B8HS
• DENSO W24FS-U
• MOTORCRAFT AE901RAC

I found a web site named MAGNUM Tuning which markets performance spark plugs and they have even listed Madeira 40/50 outboards!

I ordered two spark plugs and got these guys:

Racing spark plug for Selva Madeira 40 XS.

These "racing" spark plugs are manufactured by Brisk and the exact type is NOR14LGS.

MAGNUM Tuning states these benefits:
- Delivers 3% gain in horsepower and torque
- Notably improves throttle response
- Improves acceleration throughout the RPM range
- You can realize +5% fuel efficiency improvement
- Increases firing energy by up to 15% Flat spots cease

Brisk states this on their website:
"Our BRISK Premium LGS spark plug utilizes a very unique, semi-surface discharge electrode design. By implementing this design, the spark plug is able to fire a much larger spark plug gap, because the spark glides along the surface of the insulator, requiring much less energy than firing a traditional style air gap. Longer spark discharge makes more contact with the A/F mixture, igniting more molecules in the A/F mixture over a larger area."

My converted Selva 40 XS should produce 50 HP so with these spark plugs I could obtain something like 51.5 HP. Is that enough to make some difference ?

I installed the Brisk spark plugs and did a short test run. The engine started quite nicely, maybe a little eager than before. Unfortunately the engine stalled when I switched from neutral to forward.
This happened three times so I opened the engine cover and raised the idle speed, this helped a little but when I came back to harbour the same thing happened again (when switching from neutral to forward), my engine idle speed is quite high 1200-1300 rpms so this should not happen!

Brisk NOR14LGS spark plug being installed.

I cannot simply blame the spark plugs since the engine is running quite rough even with the stock spark plugs, maybe there is some problem with the air/fuel mixture or carburetor idle jets are dirty.
However with the stock spark plugs the engine has never stalled.

Anyway, I did some cruising with wide open throttle and didn't notice any speed gain, the sea was a little rough and thus the conditions were not perfect for accurate results.
I'm planning to do one more test in better weather conditions.