Missing top end

[TheKlic]

I was out on the Kat last night, when it started sounding funny, I didn't like it. Whenever I really goosed it, it would go but only till about 8 grand, then it just kinda didn't have anything left. When I slowed down I noticed at idle it sounded real funny, and didn't have all of the punch that it should have. I still think I could have outrun a car, but it would have been hard. It's a 89 600 and I got it from a friend who bought it from someone who had let is sit out in their yard for years.
When I got it I pulled the carbs, which were surprisingly clean, I've since changed the oil, plugs and not had any problems. So, do you guys think it's time for a carb rebuild, valve check, or something else?
thanks
BTW, I'm 17 with fair mechanical ability and my dad has owned/worked on/ridden motorcycles for 30+ years, we can do most work neccesary.

Kidd

[paradoxmd]

it kind of sounds like a fouled plug. does the idle just sound weird, or is it a little below normal?

[TheKlic]

sounds weird the whole thing, but more pronounced difference at idle
I'll check valves/plugs/carbs and hopefully find it

[slayergsxf1]

Sounds like maybe the fuel air mixture is off a bit. If the bike is getting to much air,like say the wrong velocity ring put in a K+N air filter system the bike will barely reach 8 grand.Like you said it feels like the top end is gone. Almost like the bike is goingto blow.It sounds like a carb problemto me. If it were the plugs and they were running lean there would be excessive smoke and bogging all the way through each gear. The Carbs may look clean but when the varnish that gets into the needles is what does most of the damage.