Thanks for this amazing forum, about great bikes. My wife bought a used 2007 S40 w 5000 mi. on the odometer last year after the saftey course.About 5600 now Ran great until recently. New battery installed  .New gas .seafoam . Recently it has been stalling at stop signs , usually after riding about 15 min.   I ride behind the Suzuki and have smelled a burning , plastic or some unusual  smell (not standard exhaust smell )from the exhaust before this happens.she says it struggles before it stalls. I haven`t had this happen to me ,and I do take it out.It starts but stalls again soon when stopping or slowing. We brought it to a local  bike mechanic who removed and cleaned the original petcock. Said it was not clogged or dirty. I am a  bad mechanic , but can do basic oil/air filter changes. I am going to try some of the tips on here , like testing the petcock and other checks to try to eliminate things.But if anyone has an idea where to start from my description I would appreciate it. Limited time, and tools  for this makes me ask if are there any recommended mechanics in the greater Waterbury, Connecticut area if we need one? There are some solutions here I would have a knowlegeable person do. I know  a Suzuki dealer within 15 miles , but  would much rather have a Raptor savvy guy.I`ve been there before and was not impressed, with other motorcycles. Thanks!

"[...] burning , plastic [...]"

That is often an indication of electrical problems, with hot wires melting insulation.

If it is causing the bike to stall, something may be affecting the ignition system. Have wires fallen on top of the hot engine? Maybe the rectifier isn't regulating voltage down properly?  Although it seems like a fuse should blow with that problem.

Is a hose, maybe the vacuum hose going to the petcock, getting against the engine and melting?

make sure your idle is nice and steady or at about 1200 rpm

Test your petcock and check the vac line for gas.

How much Seafoam did you use?

Have you tried re-starting it in the prime position?  I had the same issue with my bike stalling and it was the petcock.  As for the smell, we are now use to the smells of catalytic converters but when the came out they stunk.  Now we can smell non converter and they stink.

I don't know what you are looking at that lists the years....but what you want is the official Yamaha Petcock.  If you are looking at an eBay listing.....if it does NOT not have the Yamaha part number and show the petcock with the white box it comes in from Yamaha, look elsewhere.  You need to see the white box with the part number 5LP-24500-01.

http://www.ronayers.com/Search.aspx?k=5LP-24500-01

engineer wrote on 07/07/14 at 18:10:41:

This was my hunch too.

I had similar symptoms this year. Stalling, could not easily push the bike out of parking spots, smell of burning plastic while riding.
I loosened the rear brake cable, then it started acting right, but the rear brakes didn't work well (duh).
Turned out the rear break pedal return spring was not in place, it was just dangling around the motor mount. Whenever I would release the brake pedal, the weight of the pedal would  hold it  down just enough to pull the cable.

I suspect the burning plastic smell was coming from the pulley cushions.