Re: 4 stroking
Eventually you might want to experiment with a smaller jet size. At your altitude that is to be expected. We have less air up here in Colorful Colorado so we need to adjust the air/fuel mix accordingly.
I'm at 6000' and I solder and redrill all my jets. You might need to do the same. That said, I'd still put some miles on that little engine before worrying too much about performance.
You have a good carburetor in the NT. It can be made to give you all the performance you can expect from a stock engine. It simply needs to be tuned for your altitude.
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