Get the engine to full operating temp, and verify that the choke plate gets vertical. Is it a heat-tube choke, with a pipe running down into the manifold or is it an electric choke? The electrics are powered up through an oil pressure sensor behind the manifold. If this fails or passes marginal power it won't heat the choke spring enough. (I once bought a truck cheap because it 'needed a new carb at least' when in fact the choke fuse was blown) The choke stat itself may also be weak. To test the choke stat, run a jumper wire straight from battery positive to the stat terminal. If the choke gets vertical, it's the O.P. sensor. Replace it. If it doesn't help, get a factory service manual so you understand the method for adjusting the choke (The manual is less expensive than the choke stat) If adjustment fails, replace the choke stat.
Eric
