Gardo,
You need to take you Heist back to the dealer and ask them to adjust your carburetor to take out the cold bloodiness. I raised the needle with a washer and adjusted the idle mixture screw. I can fire my DF up and she is ready to go.

Have them take a look at the following to get an idea of what to adjust.
"Tuning manual for a PZ26 carb ( PZ30 on the DF250RTB/Heist looks similar except for 30mm instead of 26mm size) is located at
http://walbro.com/brochurefiles/3368...g%20Manual.pdf
thanks to jape. "