78 KZ650 C2 flat spot and stumbling

Ok, the bike is running and I have been riding it, but I have noticed one thing that irritates the crap out of me. I was hoping that anyone on here could provide some insight.

The bike will run just fine at idle, and will pick up and go ok, but there is a notable "flat spot" where the bike just does not want to perform. This is around 50-60 miles per hour, or slower depending on which gear I am in. This is all guess work, since there is no tach or speedo on the bike. Yes, the carbs were cleaned and new gaskets, float and needle installed. The main jet is a 110 and the pilot jet, I really have no idea.

The flat spot seems to run at certain throttle percentage, get it past there, and the bike functions perfectly, but get it in the range, and it spits, stumble and misses.

Now, I know the next set of questions... What about the rest of the setup goes something like this. Pod filters, four into two aftermarket exhaust (Fully open/no baffles), and I am located in the Piedmont (southern central) area of North Carolina (approx 800 ft elevation).

Anyone have any ideas on what I can do to remedy this?

had a similar issue with my bike change the needle clip position should help. what size carbs do you have? pods are hard to jet for I would try and airbox myself if you have one available. was a day and night difference for me. good luck. you want to lower the needle clip position stock position is #3 try #4 see if that helps. good luck

I'd check your points (if your bike still has them) for pitting/gap/cleanlyness.

My C2 also had somewhat of a flat spot similar to yours, although not with the "spits, stumble and misses".
I contributed it to the points set up as I had not done any mainteneance on them in a few years, and having switched to an electronic ignition, the flat spot was gone and the engine had power all the way up the rev range.

"spits, stumble and misses" does sound fuel related though. Or just not the right fuel/air mix.
Look for leaks in the carb manifolds. Maybe you got air seeping in somewhere.

OK, stock air box is out of the question at the moment since the original was lost in the fire. P.O. tried rebuilding the carbs and rewiring a few things, and managed to burn most of the bikes plastic parts off. As for the carbs, they are the stock carbs, just rejetted. Will have to try the needle clip adjustment. The points are brand new, installed them before putting it on the road. checked the spark with a spark tester and I have great spark through all ranges. So it looks like this is a fuel/air problem.

Gentlemen, I do appreciate your assistance in this.