I've read on a few forums now that the carbed 900SS runs out of steam above 7000rpm because the inlet tracts are too long. I have just bough a 900SSie engine and injection gubbins to retrofit. While looking over the injection motor I noticed that the inlet tracts are at least as long as my carbed motor. The injector bodies are a good deal bigger in diameter than the carbs and the injection motor has longer cams so I would suggest THIS is the reason that the injection motor revs better than the carbed engine and that the tract length is about right for the engine. This conclusions is strengthed by the fact that I fitted injection heads and cylinders to my carbed bike over winter and it revs noticably better but is still a little breathless.