Boxerworks.com

Last week I posted a topic about hesitation/misfiring that I was experiencing on a 1976 R90S. The motorcycle was breaking down between 3000 and 4000 rpm at slow throttle increases, but running great at full throttle all the way up through the rpms. Based on Duane's suggestion that I put my strobe light on the advance unit, I did that. And I could see that the weight arms were not opening smoothly at slow throttle increases. I ordered a new advance unit ($250) and it arrived yesterday. I installed it this morning. I now have a much better appreciation for what was happening. Either the old advance unit was malfunctioning OR my Dyna III rotor mounted on the advance was too tight. I'm not sure which. When I originally installed this Dyna III electronic ignition, I got the rotor too loose. One day when I was out for a ride, the motorcycle quit for no obvious reason. I got it home and opened it up and found the rotor with the magnet was loose so I tightened the two screws and put things back together. It ran again. Over time, I noticed the hesitation mentioned above, and I tried everything I could think of to correct it. This morning, I put the Dyna III rotor on the new advance and installed it. I could see that the weight arms would not open at all. I finally figured out that the Dyna III rotor screws cannot be too tight or it will not allow the weight arms on the advance to open. And I know from before, that these screws can't be too loose, or the rotor will come loose. I finally got everything put back together so the arms open properly (under the strobe light), and I took the R90S out for a test ride. No more hesitation!!! Nice smooth operation at slow throttle increases and full throttle. I have no clue whether my problem was from a bad advance or from the Dyna III screws being a bit too tight, but it was one or the other. Thank you, Duane!!!
DLC3

put the old advance unit back on and see what happens?

Removing the new one and putting the old advance back on would be a way to find out whether it was the advance unit or the Dyna III rotor screws. However, it is good enough for me to know it was one or the other and that the problem is corrected AND I am going to use the new advance unit anyway. There is too much fussy work setting the timing with the Dyna III and getting the screws the right tightness. I will keep the old one and use it on one of my other airheads if I ever need one again and see if it works then.

Put some blue Loctite on those Dyna screws.

Error, was thinking about the /2 advance unit.