I had the same problem, I installed a larger pilot jet (18 or 17.5 in the place of 15). Now when i open the throttle, the increase rev is correct without needing to leave the choke.
You can see on the internet site:
http://www.thetrialcompany.com/
and use the link previous and clik en 2002, then FAQ, and see diagram.
See the picture of the timing setting.
http://www.beta-uk.com/Technical/Ign00_02.JPG
I had the same problem and I installed a longer hose upwards and I fixed the hose in the guide where the cables pass.
The petrol does not leak now any more.
Thank you for all your answers concerning my problem of slapping in the engine.
Does somebody know the value of the firing advance in degrees on one 250 Beta 2003?
I wish to control with the idle and high speed with a stroboscopic lamp.
I add that the slapping also occurs with acceleration when the engine increase speed from the idle to an average mode, hot. With full mode there is no slapping and the engine has its normal power.
My Beta 250 2003 makes slappings at the time or slow down the accelerator, engine hot. These slappings make me think of auto-ignition. The level of tank of the carburettor is good, jets 150 and 31, the spark plug is normal, the engine is powerful.
If somebody knows a solution, thank you to indicate it to me.
