I recently acquired a 1977 Yamaha XS500D It ran but very rough and had a top end of about 40 mph. I have cleaned the gas tank. pitcocks & carbs. Replaced needle valves & seats & one float. When replacing the plugs I discovered that one of the heads had been drilled out and a larger plug (diameter) was installed. I replaced the plugs with NGK plugs that according to the numbering system are the same depth and heat range.
It finally ran good after I replaced the points and condenser. But only for about 20-25 miles then it started doing the same thing.
I suspect the condenser is the problem, since the points still look good. Can anyone explain what might be ruining my condenser?
Thanks,
Rusty
