This is for an original factory Yamaha piston. Yamaha part number 787-11631-03-98. This measures 2.047 in. which is standard for the 52 mm bore. The piston is from a closed Yamaha dealer.
Vintage Kart Racing, Briggs and Comer Engines Box of 10 Spark Plugs
Iridium: 8 times stronger than platinum, 6 times harder, and with a melting point 1200 degrees higher. New laser welding techniques make it possible to make a spark plug with an iridium electrode. The result is a plug that requires less voltage to spark, burns more of the fuel in the cylinder, and can spark at LEANER air/fuel mixtures (see inset diagram), resulting in higher horsepower and better gas mileage. Although the plugs are expensive, you don’t have to change them as often as garden variety spark plugs. The iridium electrode is extremely resistant to erosion, so it can last MUCH longer than a normal plug. (Longevity will vary by usage, fuel mixture, and other factors.)
Using Iridium, which is 6x harder & 8x stronger than platinum, the tip can be shrunk to only 0.4mm. This means the voltage requirements are decreased while firing performance is greatly improved.
A U-Groove has been cut inside the ground electrode to maintain the large volume of space required to form the nucleus of a flame. While still keeping the required voltage low, this technology enables excellent firing performance without increasing the spark gap.
Insulator: The insulators are made of a highly purified alumina powder, which gives exceptional dielectric strength and thermal conductivity at high temperatures, as well as greater physical strength.
Five-Rib Design: The five-rib design prevents flashover and decreases voltage loss.
Copper-Glass Seal: A special mixture of copper and glass powder bonds the center electrode and insulator together for a gas tight seal. Proper heat is maintained and hot combustion gases are excluded.
Copper-Cored Centre Electrode: A special center electrode incorporates copper into the core of the nickel chrome binary alloy. This gives superior thermal conductivity and increases the operating range.
U-Groove Ground Electrode: The originally patented U-Groove allows the spark to fill the gap formed by the U. This ball of fire develops a larger and hotter flash front so combustion is complete.
Patented Iridium Centre Electrode: Utilizes Iridium to create the world’s smallest center electrode tip for maximum firing performance and reduced voltage requirements.
Tapered Cut: Improves firing performance by reducing quenching.
360° Laser Welding: DENSO perfected the Laser Welding Process, which provides a 360° seal so reliable the electrode resists wear even in the harshest conditions.
100% Pre-Fired: All DENSO spark plugs are pre-fired at the factory to assure highest possible quality.