too rich - float level?

not really the right plan

after weening it off the 16:1 break-in mix, one still has 2 or 3 hundred miles to go before the rings get a good seat - it will stay rich until they seat

once that is over, it may still be a bit rich, so then is the time to start tuning

if curious, one can pull the muffler to look at the rings and see if the black coating has worn off yet (they'll look like shiny steel once the coating is gone and they've seated)

My motors don't get much of a run in.
But I do notice they run a little better after a tank or so. I would never run them 16 to 1?
Mabee 30 to 1 of synthetic for the first tank and 40 to 1 after that.
Did you lift the needle or lift the clip on the needle (lowering needle) I find 2nd notch from top of needle usually right.
Standard Jet is sometimes a little rich, probably depends on the pipe/ port work, but .65 for a standard set up is usually good. It also depends on your terrain, keep it a little richer for hill climbing and longer life of motor. Leaner usually means faster but also hotter.
Adjusting the float level a little is good for idle mix adjust. Sometimes the main jet isn't tightened properly and will unscrew it self?
I find em much easier to tune with a less restrictive pipe, that gives a more audiable 4 stroking sound and you want it to 4 stroke a little when it's cold, and when you back off.
But yes get a better plug.

Plug should be chocolate and stick to the 7 , hotter plug means hotter motor.
Some motors take longer for the rings to wear in, I always strip a motor before running it, sometimes the rings don't 'look right' in the bore ( put them in the barrel without the piston and check for 'light' between ring and bore, and check gap. If not good, throw away, a new set is $5. Throw away the Chinese 6202 Bearings while your in there, a new set of 4 might cost $30. If you want it to fly, check the Squish make sure you have max compression, and adjust to .7 - 1mm, Clean up the transfer ports!, and match port the exhaust (this makes a huge difference to a standard pipe).Try tuning the motor with the bottom off the exhaust, and no air filter, then put them back on one at a time and see the difference.

HT motors need at least 3-400 miles to be fully broken in. Tuning before break in is a waste of time as the engine is still not consistent. I run 40;1 in all my engines from day one and break it in by riding normally.
Wait till you run 3 or 4 tanks of fuel through it before trying to tune.

I don't mean t be argumentative, and I'm sure others here have far more experience in these things than me. If my motors won't tune within an hour or so run time, I strip it down and find out why.
I havn't done 300 miles on any of my 3 Ht motors, nor any of my pocket bike motors, If any of them had done 300 miles, I'd probably pull it down anyway just to see how things are looking in there. Sorry I find this 200 to 300 mile thing a mystery, it works or it don't?
But I have had to throw away a new set of rings! and a pile of 'new' Chinese 6202 bearings. I've had to replace brand new Mags, Twice, on 3 motors! I've also had to replace the clutch on two motors, Not even use one crank!, Totally change all ports on all motors an go through other teething issues, trying to find the carb that works best, ect. Not to mention remove foreign soil, woodchip and 'precious metals'.
But that's what you get shopping on E bay?
Two of my motors are reaching 9000 and plus after only a coupe of hours run. They may not go 2000 miles with out a rebuild? but do I care?
I want you all to look deep inside that little Two stroke of yours, and realize it's full potential.
I may be new to these Ht's but I've been a mechanic for over 25 years, and if it don't run right after a tank of gas I'd be looking for something wrong?
Hope I havn't offended.

I agree, how ever I was trying to point out that none of my motors were assembled correctly in china, and if you want a 'Good ' China girl you may have to work on it.
If you want 2000 miles of good performance out of her, get a 'built' motor, build it your self, or maybe get lucky.
Maybe you guys get better motors in the States than what we get here on E bay?
But I encourage those around me to learn.
Not say too hard, there is nothing hard about pulling these motors down, getting them back together and working right can take a bit of learning, but if your not up to it, get a better motor!

As an example, if a motor had a gut full of metal shavings and foreign soil, as 2 of mine did out of 3, wouldn't it be better to strip that motor and reassemble it, cleaning and lubricating things correctly, and 'checking over it' as you put it back together, than hoping that it helps bed the rings in?
Sorry but I feel for those that take on a Ht with little mechanical experience.

You must be getting the good ones,
the one motor that wasn't full of metal shavings, had to have the clutch basket replaced due to poor casting/ care of selection/ assembly,... At least they honored their 30 day warranty.
Another came with no grease on clutch mechanism or gears, and a crank that turns into a Masseuse above 6000 Rpm
The other came with a Bushed big end, and missing bearings from clutch basket.
2 had engine seals that had not been put in straight.
One had rings that would have taken 300 miles to bed in.
I had a Mag fail after an hour or so, a good couple of mile from home.
One set of cases had to be relieved so that the mag and magnet wouldn't hit.
...

Bore and Stroke 40 x 38?
sounds like a 50cc to me?
45x 40 is my '70cc' which has been taken to 47mm bore.
47 x 40 is my rebuilt RockSolid motor
47 x 38 is my crap motor, GT5? weird piston and rod, unbalanced crank!
And I have the 'leftover' bushed crank, that I'm still deciding is even worth assembling a motor from.

One of the things I've realized is timing makes a big difference, and as does all the different motor configurations 40x38, 45x40 47x 38 47x40, and then there's the GT5.
I bet there are even more possible timing locations! and no real way to vary the timing easily from stock, or even put a timing light on it.
A Compression tester is handy when working with these, a few spares to swap parts to isolate a problem is really good ( plug, Mag, Cdi, Carb.)
If it was me, I'd at least take the head off, measure piston so you know what you have.
I would then get a $2 Kids Protractor from where ever, and find TDC.
This is usually best achieved whilst doing a squish test with a piece of solder.
Set your protractor mounted under the Mag nut to 0 deg relative to an engine case bolt left 1/2 unscrewed, I could take a photo but .
And check your port timings, I'll probably get all sorts of coments if I tell you what your port timing should be, but It's not that hard to do. Inlet I belive should be as close to 60 deg BBDC as possible. Transfers can be anywhere between 115 to 125 deg before TDC, but usually close to 120 deg is better.
Exhaust can usualy be lifted a little, and widened I'd be aiming somewhere between 95 and 105 deg before TDC.
A little resurch will tell you which side of centre you want.
The transfer ports are YUK! A couple of Dremel Burs at $10 each and a Rotary Tool are all you need to make these flow better, And it ain't rocket science.
Again Match port the standard exhaust to the barrel, You will need the more expensive burs for that, slow hard work with a stone!This has made a big difference for me.
While you have Head and piston off you can also check that the Crank spins freely, and the seals have been put in straight. That's what I recommend.