Motorcycle Repair: TWO STROKE PROBLEMS PLEASE HELP!, stock jet, pilot jet

Question
Hello,

I have a WR 250z (2 stroker) and it is basically coughing when idling. It runs fine but when idling it stutters 'baar baar baar' instead of 'dadadadada' (hope this doesnt sound too carzy!). So Ive tried adjusting the idling and air intake on the carb and this has not worked, taken the carb apart cleaned the pilot jet - still the same problem. Checked the air filter, clean.
When riding it runs fine just really bad idling so I'm guessing its not the spark plug? I will check this next.
If you could give ANY suggestions as what I can check from here, it would be very much appreciated.
Thank-you very much,
Keanan (UK)

Answer
Keanan,
Sounds like you may be starving OR overflooding for/with fuel.  Assuming you are running the stock chamber and carb with stock jet it could be any host of carburator setting oversites. Make sure air/fuel adjustment is set correctly, typically 1 and 1/2 turns out from seated. Be absoulutly sure all orrifaces and jets are clean and not damaged. If someone used anything but compressed air and solvents to clean these they could have damaged the precise venturi action that takes place. Carburators can get pretty complex and require tuning from time to time. In addition there are different systems and effects that come into play at different throttle positions. Like your system, performance can be fine at one throttle position and terrible at another. All you can do is look closely for damage and carefully adjust all tolorances according to a good service manual. Do not overlook the float level, be very sure you are not starving for fuel. Make sure the needle valve is working ok. In relation make sure fuel flow is unobstructed and use a good in-line fuel filter from the tank to the carb. Even tiny particles in the fuel can get logged in critical areas and cause havoc.  All your tolorance measurements will be in a good after market manual from either Clymer or Haynes.  Do your self a favor and pick one up for $20, the info is priceless.

Mike