It's all interrelated. Surging is a very broad term used for hesitancy, jerkiness and poor pick up off a closed or constant throttle. Most of the components in the thread I linked to will have an effect on the behaviour you describe - TPS, CO, ECU type etc. I'd be checking the TPS (particularly based on what you describe) for both smooth tracking and the correct resistance, setting and voltage.

It may be that, by turning the fuelling mod up, you are just masking the issue, or compensating for a problem elsewhere? I don't know of anyone having to run their fuelling mod at 9 o'clock with a stage 1/2 setup (unless the ambient temperatures were well below zero).

Good call on the spark plug JTR. Always worth checking. Plus, watch out for fake NGK iridium plugs on ebay which breakdown under load. Pre 2007 XTs are harder on plugs than later models as they fire twice as often and do twice the work.

Is your fuel fresh and from a reputable supplier?

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