Hi Mori55, Always start by verifying ignition is correct first. Start by cleaning points. Then check timing. If point gap has changed the timing will change.
Worn rubbing block will close gap. This will retard timing. Not exactly one to one, but .001" gap change is approximately 1 degree timing change. As point face wears it can make pit in one face, pointed area on other face. This also can change timing. Not properly greasing point cam & rubbing block will result in rapid wear of rubbing block. Lubricam SL-2 point cam grease is very good & will reduce rubbing block wear. With good not worn ET AAU & cam with good lube you can expect good operation 1000-1500 miles. Even the modern Daiichi ignition points lasts very well.
Verify timing is correct in every case. As was stated with ET ignition timing is critical.
Then move to checking carb. What carb are you using, I can't recall.
Whatever carb, the idle jet must be clean. Start by marking mixture screw. You know where it used to run well? Mark & screw it in so you can return screw to good place. Then remove screw. Shoot carb cleaner into hole. If possible blast hole with compressed air. To clean better you'll need to access bowl. To really clean carb must be removed, unless you have Premier Concentric
I know the ET bikes can be temperamental, but properly adjusted they run well & reliably.