The "smoke" from the road draft tube is blow-by, usually caused by piston ring wear. Has the engine been stored withiout running for a while, or has the truck been in use? If it's coming out of long-term storage, the blowby might clear up a little with some more driving.
I'd begin with a compression check, looking for uniformity between cylinders rather than a particular pressure reading. A minimum pressure of 100 pounds or so, and a 10% or less variation between cylinders indicates a pretty sound engine. Very low compression, or wide variations between cylinders indicaste ring and/or valve problems. It's possible to diagnose ring problems most of the time with a "wet" compression test, with a couple of ounces of oil squirted into a cylinder before the test. If compression rises noticeably after the oil is added, you've got leaky rings. Little or no rise on a low-compression cylinder indicates valve problems.
Once you've established the engine is OK on compression, the rest is just tinkering, carburetor rebuild or adjustment, ignition timing, plug wires, etc. Find out if the engine is mechanically sound first of all.
Jerry
