dies dropping to low RPMs

[mph]

I have a 1981 xs650 I bought last summer (2016). Ran a bit rough but okay. I started putting pure gas in it and it ran better. Well the last time I rode it last year (~October) it gave me problems. I was out on a somewhat warm day and as I began to slow down to come to a stop it would die. Not just at idle but maybe as I backed off the gas and the rpms dropped. It would die and I would coast to the stop sign. It wouldn't start immediately but after maybe 5 minutes (of kick starts) it started. I rode for a while and it did it again. The 2nd time took longer, maybe 15 minutes (of kicking!) before I got it going and immediately headed home. (The starter button had fallen off so I had to kick start ). I am such a terrible lazy mechanic and it was the end of the season so I parked it in the garage and did nothing with it until today. Didn't even winterize, empty the tank. Just left the gas in it and forgot about it. Wish I had posted this right away but..

So today, 8 months later, I pulled it out. Put some air in the tires, oiled the chain and decided to see if it would start with the old gas. Huzzah! Success! Once it warmed up it ran great. No stalls or anything. And on old (pure) gas. I even found the starter button that fell off, jammed it back in and taped over it with electrical tape so it seems to be holding. BTW Today was fairly cool.

But I have no idea why it died before. Should I not worry about it since it seems to have 'fixed' itself? Any help would be appreciated. Thanks.

 

[xjwmx]

I'll probably unfix itself pretty soon. You should go through the routine for freshing up these old bikes, posted somewhere in the Tech section. The starter button -- it's kind of sensitive. If the spring gets bent just right it can fire up as soon as you turn the key on, which is especially surprising when it's in gear. So fix the button right

 

[TwoManyXS1Bs]

Looking at the clues. Bear in mind that this comes from an old coot with really old-school memories.

... the last time I rode it last year (~October) it gave me problems. I was out on a somewhat warm day

Just left the gas in it and forgot about it. ...8 months later, ... see if it would start with the old gas. Huzzah! Success! ... And on old (pure) gas. ...BTW Today was fairly cool....

Seen this kinda thing down here, 40+ years ago, when the filling stations switch over between winter blends and summer blends. Lookup "Reid vapor pressure".

Summer blend: Lower vapor pressure, harder to vaporize fuel, keeps it from boiling out of carbs during hot summer.

Winter blend: Higher vapor pressure, easier to vaporize fuel, easier cold winter starts.

Run the wrong blend during the wrong season can cause problems.
Winter blend during summer, rich conditions.
Summer blend during winter, lean conditions.

Winter blends usually cutover in October. Need to find out if this happens in your area. You may have had a high pressure winter blend fillup during last year's October ride. On a warm day, would produce a rich condition.

Now, your stale gas has evaporated the light volatles, and acts like a summer blend, more so with the cool day.

If so, your bike was probably running a bit rich last year. Now, it's a bit leaner.
Old/fouled plugs exacerbate the problem...