The standard gap for the Yamaha xs1100 is.032 for most plugs. However, the Iridium Plugs call for a gap of .044.
1978 to 1981 DT-175 with CDI (no ignition points) spark plug gap .6-.8mm or .024-.032 inch, spark plug# B9ES
1978 to 1981 DT-175 with CDI (no ignition points) spark plug gap .6-.8mm or .024-.032 inch, spark plug# B9ES
Yamaha recommeded 20/1
The 2K9 motor is either a 1978 IT250E or a 1978 IT400E depending on if it is a 250cc or 400cc.
20w50
1978 dt4
.044
I found parts scematics to view for a 1978 Yamaha Chappy here: http://www.cmsnl.com/yamaha-lb50pe-19781979_model8675/partslist/B-01.html
That would be a 1978
7.3 to 7.5 fl. oz.
0.045
The gap should be .02-.03in, but some manuals will tell you to go slightly bigger. It should be listed in a manual, which you really should get if you plan on doing any sort of tune ups on your bike.