I had my 2012 S40 in for routine maintenance. It has never had an issue in 10 years and now it is stalling badly, to the point that once I get it running again, I can only get it home by keeping the engine revved up, holding in the clutch when I have to slow down or stop, and continuously giving it gas. I can also get it home if I turn the idle up real high, but that doesn't fix it permanently. I wonder if they could have done something during the maintenance to cause this problem. I brought it back to them and they said it was running too lean (due to the adjustment at the factory, which made no sense as it ran fine for 10 years out of the factory). Anyway, it ran fine for a few short trips but is now severely stalling again. I called them back and they insisted that that should have fixed it and were very rude so I am done with them. I'm hoping someone here may have some ideas. One odd thing...my bike has always had a mild but fairly consistent backfiring issue. Nothing that ever really bothered me, and I've read that this is not uncommon in S40s. Now it no longer backfires but has this stalling problem. Could it be related? I'd take the backfiring any day. Could they have adjusted something at the shop that stopped the backfiring but in turn caused the stalling? Maybe it's just coincidence but it does seem odd enough to warrant questioning. I am not a mechanic in any shape or form, so any ideas would be greatly appreciated.

 

Perplexing problem.
Stock S40s don't backfire. Modify the intake or exhaust and it will backfire like a Model T Ford.
What kind of service was performed?
Check for spark next time it stalls. That will narrow down the problem.

 

The symptoms make it sound like a clogged carb that needs a cleaning.
Has the bike sat very long without running? That will clog it up.

 

It hadn't been sitting, and I only put ethanol free gas in it, but I think cleaning the carb is definitely worth a try. Thanks!