23jay is right...if jetting hasn't been changed, of course it is an issue.
For a few bucks you can put a 12T on the front. Works with the 108link chain. If you don't like it, you can change back to the 13T in a minute.
IMO and all, but getting the head milled is a great big mistake! There are tons of things that will improve your bottom end without increasing the static compression ratio. Detonation is enough a spectre as is without TRYing to make the situation worse.
What's 'gnarly' mean? 30 or 35? If it's bottom end you want, you should have a -35. If 'on the pipe' happens at 1/2 throttle, I'd guess you have a -30. Wrong pipe for you, then.
It's pretty simple to get your bike to be a stump puller. Other riders talk of pulling the front wheel with a flick in 1, 2, 3 AND 4 at times.
Jet it right. Gear it down. Run a pipe that fits what you wanna do. Change to either boyesen 607 reeds or get a DeltaForceII reed setup. The 220 is a torque monster.
If you're trying to make it into a 426...that's a different story.....