Sounds like a carburetor problem. Make sure the choke
plate, on the top of the carburetor is fully open when
the engine is warmed up. Remove your spark plugs and
look at the electrodes. Are they black and sooty! If so
that's an overly rich air to fuel mixture. Too much
gasoline and/or not enough air. Are the electrodes
white? If so you have an overly lean air to fuel mixture.
Too much air and/or not enough gasoline. Also check
the EGR valve, if equipped. If it's not closing all the way
you will have a no idle/stalling condition. Remove the
EGR valve and clean it. Make sure it's closing properly.
If, after you've cleaned it it's not closing properly it'll
have to be replaced. Hope that helps! Jim