Sounds to me like you're simply rushing it. If it runs fine as you say when it's warmed up, then warm it up before you drive it. These things don't run like EFI cars.
One thing you might look at though, is the exhaust flap in the exhaust manifold. If it has frozen up, that could have an effect on how the engine runs, especially if it is frozen in the position that does not allow heat to the bottom of the intake manifold.
