Buttoned up, fired up and it's about the same.
When I ran it before I did not muck with it much. It was run, had smoke out of the carb so I stopped and opened it up to get the valves.
The stems seemed fine, no gum or buildup.
On firing it up after lapping there was no smoke and it ran well. While adjusting the carb it broke into the smoke mode. It's like a backfire out of the carb throat with white smoke which is from the bore. The backfire is regular and always there each cycle. If the engine is throttled down the backfiring will stop and it will idle fine. It can be snapped to full speed and the response is very quick. At other times snapping the throttle will make it go into the rapid backfire mode. Going low throttle clears it.
While running at full speed well it will break into backfiring when adjusting the high or low limits of the high speed jet. The sputter from running too rich or too lean is just enough to make it go into backfire mode sometimes.
If it's running fine and some choke applied to make it run rough that also will cause it go into backfire mode. Going off choke and reducing the speed will clear the backfiring. Going to high speed quickly wlll cause it to go to backfire mode about 50% of the time. Going to full speed slowly usually does not cause it to go to backfiring. It can go along at full throttle for quite a while clearing a heavy load with minimal engine sag. It runs at times like the engine is very strong. Occasionally it will break into backfiring though but clear quickly with lowering the throttle.
Causing the engine to run rough makes it go into backfire mode. One time when backfiring out of the throat I put my and up to the exhaust stream. The stream was not the usual puffs but a steady stream of air. The exhaust valve must have been stuck partly open for that. ?? On the intake side the backfiring is always puffs and never a steady stream of smoke. It's a steady regular series of puffs.
Later:
Checked the exhaust when it's getting white smoke out of the carb. The exhaust stream is not steady but in puffs as it should be.
Added Later:
The engine is not stuck at half throttle as mentioned in prior posts. It can run in the backfire mode at idle or close to full throttle. When it's in backfire mode speed can be changed and the backfiring continue during the change.
This message was modified Feb 12, 2011 by trouts2