Did a routine maintenance on my recently bought 99 Harley sportster 883 with 14k miles on it. I changed the plugs, changed the oil(switched to synthetic assuming they didn't) had the carb rejetted and cleaned the air filter. I run the engine to let the new oil filter through and surely enough I get white smoke come out of the rear exhaust once the engine has warmed up. I notice it a bit low and add more and it looked to have gone away but I do notice it idling at a higher RPM and seems to be riding a little rich. I decide to take it on a ride up to the Rock store in Malibu to see how the bike performs. Naturally after the ride I check the spark plugs to see if I can read anything on the bike.

My rear cylinder is soot black and dry as if I need to put a new plug on it, my front cylinder is as clean as a whistle. After hours of researching on the internet I've come up with a list of possibilities(mainly air intake leak, cracked valve guide) I don't usually post threads but I feel like I've been running around in circles with this.

Thanks for reading, I appreciate any advice.

 

Questions:

What size jets were installed and how was the jet size determined, on a dyno?
Did you "pre-fill" the oil filter before installing it?
Have you tried checking for intake leaks, particularly where the manifold meets the front cylinder?