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Joe Bowen

So after attending my first race last weekend and looking for nothing but “Seat time” I quickly learned that with a kart not running or tuned for the weather conditions made for a long day! My kart ran great on Friday with a 160 main jet NGK BR9 plug but then Saturday temps were cooler and the kart wouldn’t hit high RPM (I call it power band like a dirt bike) until at least 100′ further down the straight than the other karts. So I tried a smaller jet 158 but that wasn’t enough. I was also told the spark plug I was using wasn’t optimum for the Rotax so I question What plug is best and can you use a hot or cooler plug to tune the engine like the main jet?