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[CaliforniaRider]

So this started a few weeks ago. I have a 2011 classic 500 efi with UCE engine. Never had any mechanical problems before this. Engine runs fine idling, but stutters and backfires when accelerator is turned and then recovers. I cleaned the air intake and replaced the sparkplug without any change. It feels like the timing might be very slightly off. Anybody know how to test this or have another idea what it might be?

[ric]

If happening when the engine is warm (and when it's operative) it might be the lambda sensor in the exhaust down pipe has become dirty. Carb/Brake cleaner can be used if the dedicated cleaning product is not at hand.

[ric]

Or a collapsed fuel hose...

[hagis]

Unlikely to be timing, more like spark plug cap - try a new NGK cap and or new spark plug.