pony problems

A couple of things come to mind:
Most common source of blow by and smoke from the crankcase is worn piston rings which also goes along with loss of power. The other thing is the bearing fit may be to tight when the engine is warm. Actually could be any number of things causing loss of speed/power. Governor operation, carburetor adjustments, timing, air intake, etc.......but the only two I can think of that would make smoke are the first ones I mentioned.

An engine with a recent overhaul would have some blowby gas until the rings seat properly. Maybe not a lot, but some. Is the crankcase breather open? how is the compression of the cylinders?

About the bearings, when it has just been run and won't perform properly, stop it and immediately try turning the flywheel by hand and see if you can feel a tight bearing.

the governor can be manually overridden or disconnected from the throttle to see if that is the source of the trouble.

Late cam/valve timing is supposed to produce a sluggish/weak engine, as a matter if fact, I'm driving one everyday that acts like that :>)

Good advice except you will have to resort to the hand crank to manually turn the pony over. The flywheel is not exposed on the D7-17A D339 engine.

Hi sweman,
OM and CC have given you a start but I have encountered this problem several times with those unfamiliar with these ponies in the assembler leaving out/omitting the spacer washers-- ( I think P/No 2B4219, not always shown as a seperate part but a part under the Block Grp. Only have 3T & 2H books)-- out (off the studs) and crushing out the clearance built into the main bearing bushings. If the engine is tight to turn over maybe loosen the main bearing stud castleated nuts a little bit and also the smaller pan bolts and see what happens--maybe too late and damage is done!!!!
Hope this helps Eddie B.

Found them:
Part # 2B4219.....one on each stud.
Also covered in the D339 service manual with warning and consequences as edb describes. Also words of caution about carefully aligning gasket around the spacers.