Contray to the previous post, not ALL K&B's are problematic. However, with that said, I will agree that the (early) .45 Sportster is probably not one of their finer efforts. As the first reply said, they probably had more problems with the .45 than any of the other Sportster line. One mod not mentioned was that in later versions of the .45, they machined most of the cooling fins off the head to correct an over cooling problem. If yours has VERY short cooling fins on top of the head, yours may run OK. Also, as with the other engines in this line, the engine is NOT set up to be a high RPM engine. However, it WILL turn a much larger load than most .45 sized engines. While it may seem guttless with a 10 x 6/7 prop, try something larger like an 11 x 7. I found they would turn these props about as fast as the smaller props and make a lot more thrust doing so.

Good luck,

Lee