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Starts and idles fine, when revving or accelerating to 40+ starts missing a little like it might be fuel starved, but will get up to at least 50 usually. Laying off the gas at speed induces backfires, which I wouldn't expect if fuel problem.

Has aftermarket electric fuel pump - replaced! Also replaced automatic petcock and spark plug, still has problem. Checked air filter, seems OK.

Ran some Seafoam through, didn't seem to help

Not sure how carb can cause backfiring like that and starvation.

Haven't adjusted mixture - too rich?
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mileage?
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16K!
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you check and adjust your valves yet?
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Nope!
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Start there.
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Done. To my surprise, they were perfect: .004, .006
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check the spark too

remember, if the carburation is poor rpm is higher and the engine temperature high soon.

if rich is quite opposite
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UPDATE

Went for a ride last night, about 12 miles I think. The scoot was missing and bucking as usual but not running the worst its been. Got about 1/2 tank of gas before driving home.

This morning the scoot is running perfectly - humming along at about 60 down the highway. It's tempting to think bad gas, but I don't think so, unless I've had a couple tank fulls, as its been acting up for about 3 weeks and been filled at least once in that time, plus I added Seafoam a while ago which I think should disperse bad gas.

I should note a couple historical problems that seem related. When I first had the scoot she would sometimes flood - spilling gas out once or twice. My mechanic remedied that, not sure how, I don't think he replaced the auto petcock valve - rather adjusted the carb, I think.

Once he had done that she began to have gas - starvation symptoms similar, but not exactly like the recent ones. I finally added an electric fuel pump which made those symptoms disappear, but didn't touch the carb.

My mechanic sold his shop and I never found out exactly what he did to the carb, maybe adjusted the float? I don't know! I'm suspicious that the intermittent problems I've been having are related to his adjustment, maybe? The problems I had before adding the fuel pump were very intermittent.

Intermittent problem are the worst! I'm expecting the problem to return at any time!!
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