Veco Montague's post above is dead on and an excellent outline. Now for your Sportsters all of them 20, 28, 45 and the 65, the K&B 1.5v long idlebar is an excellent match and yes the little 20 needs the long plug. For the K&B 61 this one works well with the idle bar but is also more tolerant of ones without and as mentioned above the K&B 1L is fine.

John