Long time member who hasn't posted in a long (long, long...) time and hoped someone would have another idea. I bought an 03 spirit a few months ago and it doesn't run quite right and can't seem to figure it out. I had an 03 spirit several years ago and it was perfect, so I know it's not "normal" even though several people tried to tell me this. The only thing the original owner said is that it has always run like this (assuming from the factory). Who knows why he didn't take it in under warranty, but thats way too long ago.
When you ride under about 15 it backfires out the airbox side of the carb on only the front carb pretty consistently, and when you downshift at speed (maybe 25+ mpg) and don't hold in the clutch it backfires pretty badly out the exhaust side, again only on the front carb. The back carb/exhaust doesn't at all.
Maybe I'm missing something, but here is what I have done and checked:
I pulled the carbs off and disassembled them and they were immaculately clean for a bike under 6000 miles and 6 years old. At the same time I checked everything to make sure there wasn't anything in the fuel or if one of the lines was pinched. I Checked the jets and all the airways to no avail. The following weekend I pulled everything and adjusted the valves. All of them were within tolerance except an exhaust valve on the back cylinder (not the one backfiring). the last idea was to pull the factory settings off the carb synchonizing screws (can't remember the techincal name) and one side was 2 turns in the and "bad" one was about 1.5 turns. They are now both set about 2 and 1/8 turns out and it seems to have taken away the random backfiring at idle, but it's definitely still there the rest of the time, so maybe I am starting to get on track?
The only other ideas I have are to get the actual tool to synchonize the carbs. It doesn't seem to matter as the front one is always bad and the back one runs great, so I don't think it has to do with that part. The final thing I can think to do is advance or retard the timing to see if it makes a difference, but I was hoping someone had the same problem and has an easy fix without a $500+ factory bill.
One final thought after posting this originally - I am 99% sure it hasn't had a jet kit installed at any point in it's life but I'm not 100% sure. My original shadow had the exhaust drilled out so maybe I missed the backfiring because it was so loud?
From the land of Dorothy & Toto