Bog at high rpm's

Bike runs good and strong between 2500-7000 rpm. At between 7-8k it seems to really bog down and run rough, but then picks back up around 8000-8500. I've not had it above 8500, kind of a little scared to go higher. What could be causing this?

Also below 2500 it kind of bogs too. Like I need fairly high rpms to take off, and starting on a hill from a stop is nearly impossible. Not sure if that'd be related.

Did you clean out the carbs yet? I checked another thread you had about the Stale Gas The stale gas may have fouled up the pilot jet (under 2500 rpm problem) and the main jet (over 7000 rpm problem)

Well, no... hadn't done that yet:unsure:
I'd say you nailed it. Guess I'll venture into another unknown this weekend. But, learning is one of the things I love about owning a KZ.

Ma Kaw says that you have a points ignition. Is that correct? If so my bet is that your problems are unrelated. The low RPM problem is caused by the idle circuit. Either misadjusted, blocked or just plain the wrong jet. The high RPM problem is caused by the points breaking down at that RPM. My 900 still has the same problem. The points have to be at top shape and perfectly adjusted to run at that speed cleanly.

KZCSI

It might be a good idea to take off the carb boots (the rubber intake manifolds connection the carbs to the cylinder head) and resealing them with a silicone adhesive. These rubber boots eventually will dry out and crack without being visible.

I noticed that when I had a minor air leak the motor sometimes stumbled at high rpm. This is a very simple task and can save you some headaches down the road.

Cheers - Colin Firth

1977 Kz650 Custom - 14,000 original miles, bought new by brother in 1977. Current re-incarnation includes- 810 Wiseco, WG Mikuni 29 Smoothies, 750 GPz cams, intake valves, modified head, Dyan ignition and coils, plus too much more to mention. Painted Moon Dust Silver to re-create factory paint scheme. Not much can keep up with this old girl up to 70 mph. This bike will never be sold and probably passed on to my teenage son when his testosterone levels off!

1982 Ferrari 308 GTSi. 3.0 litre, aluminum V8 Four Cam Engine with a sweet shifting five speed. Rosso Corsa Red with tan leather interior. 56,000 miles. Looks and rides like it just came off the showroom.

2007 Toyota FJ Cruiser. The yellow tank that will go anywhere-anytime!

1998 Jeep Wrangler TJ - 6 Banger with a five speed.

2007 Chevy Uplander (for my bride)