1980 kz250 revs up

[CC898]

My brother and I came upon an old school 1980 kz250 that seems to be in really good shape. Only issue is that it will rev up to just about red line totally randomly. We can start it up and it will idle fine for a little while, it will only start and run with the choke on, once we shut the choke off it will die, and then totally out of the blue will rev up with out giving it gas and will stay there for a few seconds and then go back to idle, then shoot back up and so on until we shut it off. I honestly don't know that much about these old of bikes, so I'm hoping someone can point us in the right direction. 

 

It kind of sounds like an air leak to me coming from a two stroke background, but I wasn't able to find one. Are there any sensors that would make this issue happen if this bike even has sensors? Thanks in advance for any input! 

[The Spanky]

I'll agree it has an air leak, along with clogged carb circuits.

 

No sensors of any kind on that engine. The only electronics on it is the ignition module.

Edited March 22, 2015 by Chokey

[mickeydee]

It has an air leak. Spray brake clean around the airboots when running when cold and hot and if you get a reaction you have an airleak.i would disassemble and clean the carb too( use Honda,Yamaha or Suzuki carb cleaner. Works the best