'89 Kdx 200

[Parker Kdx]

Hi there, I need some advice on how to check the Exhaust advancer spring... I've just taken the exhaust valves and operating rod out and serviced them, the bike however still doesnt operate very well at low revs and im not sure its hitting the powerband fully. The compresion is good and checked most other possible causes.
How do i check if its the advancer spring, or any other idea's on the cause of the problem?

 

[dirt bike dave]

Not sure how long you have had the bike and how it used to run, but FWIW, the stock jetting is way too rich.

 

[Parker Kdx]

I've only had the bike for about a month now. So do you think I should change the jets or try retune the carb?