How to have the cleanest running two stroke

You over looked the most important aspect of a clean crisp running bike, jetting. You don’t have to do any of that other stuff you mentioned, like literally none of it.

I would agree 99% of the time…except for 02-07 CR250s. You’re chasing your tail unless you fix the squish, at a minimum.

I agree with both post above. Depending on which bike you have sometimes it takes some engine mods before jetting but in most cases if you dial in your jetting you’ll have a bike that rips bone stock. As with any two stroke make sure you have no air leaks, good reeds, good compression, and fresh packing before you start chasing the crisp running bike you’re after. If any of those are not up to par you are wasting time and money chasing something you’ll never get. 

Jetting is always a good idea, and it will run better, but the "secret sauce" to getting "apple excellent" is getting the head right to go along with the jetting. 

These guys nailed it. Get your head setup for the fuel you’re going to run and then jet accordingly. Way cheaper than all that stuff. 

Vforce 3 with a spacer to smooth out the powerband.
Heavier flywheel.

PNWMX and the other posters discussing squish are absolutely correct.  The stock squish on the 05-07 engines with dome top piston is 0.084"- extremely large and needs to be corrected.  But tightening the squish clearance alone is not enough.  The squish taper angle, squish width, dome shape, resulting head volume etc, etc are also very important.  Take squish measurements and send your head with test solders to a competent builder.  The result will be substantially improved jetting stability, and a better running engine.

Jetting I hv a tackle box full of jets. Pilots, 1/2 leaner,richer needles with clips in the middle slot, a few mains. A 04 cr125 has very finicky jetting. I usually do 2 rejects a day but could do 3. The cr250 is finicky also. Wore out reeds make a bike run crappy also. Pc did the head when they ported I,m sure. Run race fuel or a 50/50 mix. IKat helps with throttle response & under a ld pulling hills. Cuts down on rejets it might be a little off but not as bad without the iKat.  Run a gear higher to lessen the hit or drag the rear brake. 

Maybe try a Flywheel weight on the CR250,  that should tone it down ....spending some cash on training and practice doesn't hurt either . 

Ride a 2023 KtM 300SX…. And never look back👍