How bad is a slipped timing belt/chain on a 1989 Harley 1200 Sportster?

I dont think you have a timing chain problem My guess is an electronics problem if the engine is ok, you need to do a compression test and see what it is, then go from there, if the compression is good in both cylinders then something else is wrong. In any case, you need to buy a shop repair manual, or go find a good harley mechanic and go to work. the piston has to go down, (which pulls air and gas in , before it goes up(compresson stroke ) and fires, the sucking is ok.thats part of the cycle for a four stroke