First "long" ride

[highgear]

So I recently scored a 1976 XS for basically nothing. All original with 14,000 miles. When I got it, it had the common hanging idle problem and a pretty good back fire out the left exhaust. After researching this site I ordered a set of advance springs from Mike's XS, set both carbs mix screws to 3 turns, filled her up with 93 octane and started using Star Tron fuel additive per a friends recommendation.

By the 2nd tank of gas she's purring beautiful, 1,400rpm idle, easy starts, pulls hard to 7,000rpm in 1st through 3rd gear, probably would in 4th and 5th but I don't have the nuts to try.

So I decide to ride about 150 miles. After about 2 hours, I noticed a little puff of white smoke on the left side. Not constantly though, and only when taking off from a stop. Checked the oil and it seems fine. It still runs fine. I haven't seen anything on here that really describe it. She's not pouring smoke or fogging anyone, just a quick little puff. Any ideas?

 

[TwoManyXS1Bs]

... scored a 1976 XS for basically nothing...
... All original with 14,000 miles...
... pretty good back fire out the left exhaust...
...noticed a little puff of white smoke on the left side...
...only when taking off from a stop...
...just a quick little puff...

Just noting the highpoints.
There may have been a history of lean-burn and high heat on that left side.
Age and originality can also mean old/worn guide seal(s).
A sparkplug inspection may reveal more.
Something to keep your eye on...

 

[gggGary]

A bad valve seal is likely on a 40 year old engine. At least one valve is always open on an XS650, left sitting for years, decades, that stem often rusts. The rust can grind up the valve guide. Common for a valve to stick open and get bent by the piston on "Wake up runs". I try to be very religious about opening the valve covers and pulling the plugs, hit both areas with rust buster and oil do lots of kicking, cranking before a start is attempted. But that won't stop a split or rock hard valve seal from letting oil down the valve stem.

 

[highgear]

I'll definitely have to read up on valve train maintenance.

I racked up about 120 miles doing short 20 mile rides with no smoking. Guess when I get it home I'll pull the plugs and go from there. My uneducated assumption was either the longer trip got some gunk hot enough to burn off, finally got enough time in to start burning it off, the star tron is cleaning, or a combination of.