I posted this about a year ago: I used Shell Rotella non-sythetic oil in my Fjr for about 28,000 miles, from just after I bought it new in 2004. I live in Redding, Ca., hot in the summer. At ~25k mi the bike had a low speed bog or lack of power at under 1800 rpm. I couldn't solve the probem and have good mechanical skills. At 29k mi the bike wouldn't start so I took it to the dealer. The mechanic called and said the compression was very low and the head had to come off. I went down to look at the parts and the intake sides of the butterflies were black with soot, a coating that could be scraped of with a fingernail. The mechanic ask what oil I used, I told him, and he said a diesel oil was a bad choice and to use a motorcycle specific oil. Enough of whatever cooked off the Rotella oil had enter the combustion chamber via the crankcase breather to leave very small carbon deposits on the exhaust valve lands-and it doesn't take much to lower the compression.
$1500 and 11,000 miles later everything is fine. I'm using Yamalube now and have had the air box off twice to looks at the butterflies, they are no longer coated with soot.
A diesel engine has about double the compression ration of a gas engine. A mechanic told me the extra compression of a diesel was enough to force more oil out the the rod/bearing interface during the compressin stroke. His opinion was that diesel specific oils had properties/additive to keep the oil film thicker, and perhaps it was these that caused my problem.
I've seen a number of people questioning the use of Rottela, so my experience may be helpful.
Jim
