That depends on your defenition of 'much'.
Is it a huge difference? Not really. Is it enough to warrant the small cost? I think so. I used a +2 in my engine, and it brought the power curve up all the way across. The +3 that worked well in the F2 engine didn't work as well in my F3 as the +2 - just a heads up. Peak difference was maybe a couple HP, but the power was stronger all the way there.
They are cheap, and a snap to install, so my opinion was it made enough difference to justify the small cost to me.
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