CR250 Surging problem

[BarBQd Iguana]

I am new to the world of dirt bikes. I am 35 and didn't get on any type of motor bike (the girl's '97 CR250) until about 2 months ago. Since then I have purchased a '06 YZ450F and am learning to ride (trails). Anyway, the girl and I want to go ride but her bike is having issues that I am not sure where to start diagnosing. Here are the details that I know:

The Problem:
With the choke pulled out the bike starts and runs. After warmed up the bike will surge (idle up, come down, idle up,..etc.) at idle and occasionally when riding. This has caused some scary moments when riding and not wanting a surge in power.


-'97 CR250
-Bought in Utah at an altitude of around 4,000 ft. Currently the bike runs at around 500ft.
-Changed the plug
-Drained and refilled fuel with a 40:1 mixture
-Replaced the CDI module (it was needed as a wire had broke and was crudely soldered back together)
-Cleaned air filter.

Can anyone give insight as to what would cause this and what posible remedies would be. My knowledge of 2-strokes is limited. only what I have figured out so far from tinkering and reading in the Clymer.

TIA

Mario

 

[john stu]

its sounds like your bike is running lean at idle could be it needs richer jetting or it could be as simple as a dirty pilot jet

 

[john stu]

also make sure you dont have an air leak

 

[84cr125]

i get the surging problem your describing, but only when i run out of gas. I think its a running lean symptom.