Modern Vespa

Not Vespa related, but it's a scooter. My 2011 Yamaha Zuma 125 with 35K miles stalls when it's been ridden a while in hot weather. It happens not only when it's run wide open; it has stalled when I ride stop-and-go at 30 mph around town. Once the stalling has started, I can pretty consistently get it to stall if I open the throttle quickly, but it will also stall when it's only idling. After cooling off for about 15 minutes it will start again. In cooler weather (less than 80F or so) there's no trouble.

The 2011 Zuma 125 is fuel injected. The valve clearances have been checked since this trouble started and are right on. The spark plug is fairly new. I'm hoping to narrow down the cause without having to test the fuel pump and injector -- it's a bear to work on the engine, not as simple as lifting out the pet carrier bucket on a Vespa! Could a faulty coil cause the stalling?

Any help is appreciated. Thanks!

It does sound like an electrical part is failing, and overheating.
O.S.

I had a Zuma 125 and they always run super lean from the factory. There used to be a guy on Zumaforums that went by RC Concepts that got all the goodies from Taiwan and he sold a higher flow injector. Mine would overheat on hot days as well from day one and was told its normal because its air cooled. Always suspected the ECU myself. I ended up trading the Zuma when it wouldn't start when cold, that I later heard was from a sharp weld under the floor board cutting into the unprotected/non-loomed wires. And yes, it wasn't a easy scooter to work on.

A failing coil could explain this: when they get old and hot, the insulation around the tiny wire windings can fail, which prevents a proper spark from forming.

Also check the integrity of the wire from the coil to the plug.

It's the fuel pump. Google "yamaha fever"

Yamaha did have a fuel pump recall if I remember correctly. Look into it.

That was in 2009. I think the problem would have been corrected by the time the 2011 models were built.

The fuel pump is expensive and a lot of trouble to replace. I want to rule out other causes first, or find positive evidence that the fuel pump is bad before throwing money at it.

Thanks for your help!

A fuel pump with a lifetime guarantee is $13.00. Once you get the plastics off, it's 6 bolts to remove the pump housing from the tank. I've replaced over 30 Yamaha fuel pumps in the last 9 years, 50cc Zumas up to a Tmax. These problems go back to 2007, and continue into 2012/2013. Even when Yamaha would replace one under warranty, they would put the same crappy Chinese pump back in. This Tmax was done under warranty at a Yamaha dealer only to fail again 20,000 miles later. When I pulled it out, it was the same shiny silver pump stamped Made in China. You can keep asking the same question hoping to get a different answer. When it's all said and done you will need to replace the fuel pump. https://www.ebay.com/itm/232910196202?epid=1455768543&hash=item363a878dea%3Ag%3AE3UAAOSwIgNXnARQ&fbclid=IwAR3lXnjsLCF9T5AB79jNEB7gZkTCPQh7ZJrBVRl6zL_RJg2qIUX_-yYe3Yk

Thanks, Abner.

That fuel pump on eBay says it’s for a Zuma 50. Does it fit a Zuma 125 too?

I know something... :?

...and?

I changed the fuel pump twice but with long waiting times ... T Max sold ten years ago.

Same pump. 30mm in tank pump.

I put a new fuel pump in and that seems to have solved the problem, though we haven’t had the really hot weather again. Not too difficult. The hardest part was snapping the pump assembly apart.
Thanks everyone!

Sounds like some bad timing, assuming the Zuma was your 10K Scoots choice. Fortunately you have a backup.

Keep that one going for at least a few weeks, please!

Yep, the Zuma is my 10K Scoots ride. The BV is next, just needs a spark plug.