NGK Iridium Spark Plugs - Cheapest horsepower for your XS you can buy ! BPR7EIX - Fits: 73-84 650's - Adds a solid 2 HP to your 650 While Dyno testing a problem bike (a TX750) it was discovered that customer supplied Iridium spark plugs caused the engine to gain 2 HP. Further Dyno testing on other stock and modified 650's showed the same results! The gain seems to be from improved combustion chamber flame front spread in the 650's old style combustion chamber. The same results were obtained on engines with points, factory Tci and Boyer ignitions. We determined that the shape and position of the nose and electrode caused the gain and not any enhancement of spark. Smoothing of the dips in the power curve, increased acceleration, reduced fuel consumption and up to 4 times longer plug life can also be expected.