Kz200 Sputters, bucks, then dies

Hello there kz riders, new to the forums, and to kz's.
jsut picked this 78 kz200 up, and fixed it up. there is a bit of a leak from the two halves of the head, like oil slowly and minutely sputtering out of the gasket (or where it should be) then burning on the head. perhaps that is where my performance issues lie.
so here is the list of what i have done:
cleaned carb and tank of 15 year old gas.
new float and float needle
new coil
new condenser
oil change, new filter
cleaned points
new battery

so here are my symptoms.
i run for a bit and it goes fine. then i try to get it up to maybe 45-50 mph and it starts bucking. like accelerate....nothing....accelerate...nothing. then i slow down, it runs a litter better, but once i get to maybe 10 mph it dies and i am on the side of the road. i usually contemplate life for a bout a minute, then try to get her started again. i will after some choke fiddling and a few pushes on the starter button. then, again, it runs great for a while, and as long as i dont try to go too fast it will be fine. but i really want highwayspeed!

i am going to go do a plug chop after this post and i will come back with my results.

\-Joe

It sounds like a fuel problem to me. I know you said you cleaned the tank and carbs but I would clean every thing again. The jets could be cloged or possibly the screen on your fuel tap could be cloged also.

Plug was good, light brown, not sooty or oily. tightened chain, it was scary loose. and i guess it is time for another carb cleaning. i think iam all out of carb cleaner though. oh well. we will see how this goes.
previous to this my only experience has been with mopeds. so its nice to be working on a single cylinder motorcycle, but this carb is a lot bigger than what i am used too. and the jets scare me. i can actually see through them!

hey bud, try disconnecting your fuel line from the carb, open the petcock and see if it looks like good flow. I had this problem as well, ran for a couple minutes, felt like it was running out of gas.
Also check your gas tank itself for rust or particals, make sure your petcock is working, make sure you have enough gas to be in the on position, try reserve if you can. Check your fuel filter, and lastly, but not leastly, check your float level.

Before I pulled the carb again I would stick a funnel under the carb and open the drain screw to ensure fuel is flowing freely (engine OFF and no smoking!). I had a similar problem a few years ago and it turned out to be just a kink in the fuel line. If that looks good, the next time it happens crack the gas tank cap open to be sure it isn't just a tank vent problem. Ed