Boy oh Boy it seems we all have these problems . I never found a "trick" . I did use a vaccum pump and even thats not foolproof . Some folks swear by " SpeedBleeders". For me I just ended up letting about a pint of fluid gravity feed out the caliper bleeder.....be sure to never let the reservior get to low while doing this . When the air is all gone these bikes have pretty good brakes for there weight . Here is a link for some reading I found with the search function .
another item that comes to mind---how old are your brake lines? my 83 is a bit on the soft side and expaned when pressure is applied . giveing that at sponngie feeling . going to replace with the stainless steel ones . i got mine coming from a menber on the forum . give lopeha a pm and save yourself a few bucks.