It would most likely be in the carb, first make sure it is not restricted, and check installed jets as to what was stock,
With todays oxygenated fuel , you need to make the pilot system a bit richer, When it sits and idles and rev it, does it come down to a clean and steady idle?
Or if it revs and stays on a high idle its possible way to lean..
If there is a lot of blue smoke out, then its possible you might have a right hand crank seal leak.
Try a few of these things and re post, I know the old bike very very well,, will do my best to help.......
One other thing you can check... pull carb and make sure the float is working correct, is it a aluminum needle or one with the rubber tip.
If it has a rubber tip, take a Q-tip, put in a cordless drill and stickk it in the needle seat and go to town, go in and out and push the tip into the seat.
If its a aluminum you need a bit of valve grinding compound. do same,
clean out with carb cleaner and give this a shot...
nwcycle screwed with this post 04-16-2013 at 06:29 PM