surging

jazak5 said

suddenly started to surge while cruising at 55mph//never had this problem//with a 1yr old rebuilt carb

mash the throttle//no response !! but will hold 55mph

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By any chance was this right after filling up?

Running lean can be getting extra air. But
can also mean not enough gas or
contamination of the gas..... like water, or
the wrong fuel for the tune; like E20 gasohol in a premium-tuned engine.
Or something really simple like the metering rods not working.