so I bought my first two stroke - an RM 250 twostroke that was blown up, and rebuilt it just for fun.

Runs/idles good, but the power delivery is not consistent at all, particularly at partial throttle. Is this just the nature of the two stroke bikes or do I need to play with the jetting? It's basically slightly richer than stock jetting that I believe the previous owner richened up after he put the aftermarket exhaust on.

Carb is clean and freshly rebuilt, brand new throttle cable so it's not hanging up at all.

Any thoughts? Just got done with break-in so trying to figure it out

First thing to do with any 2 stroke is put a new plug in it. JMHO

Brand new plug and wire. Gapped to OEM specs

u got an old school motorcross bike
they we made for wide open throttle at high rpms
very doggish rolling throttle loading motor,,,,,,
when they get to the powerband u hold on,,,,lol
I still have my old honda cr250 sitting in my garage from when I used to motorcross
till I broke my collar bone on it ,,,,so sat it up in the corner for time out been there since

That is my opinion and I am sticking with it.

My first dirt bike was in 1960

Could be you so you will need someone that nows dirt bikes to drive it and see if an issue or not.

2 strokes have an extremely narrow power band. Especially motocross engines. If you are in the wrong gear it ill be a dog.
Correct gear and you punch it...hold on and keep shifting

Pretend you have a 302cid smallblock with 270/280 at .050" cam and 102 LSA.

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woo hoo

I like the 69 Z28 # matching 350 car.............

I owned an RM250 for several years.
Mine ran just fine at part throttle. A 250 should pull well even if it's not in the ideal gear. Not like a 125 that will fall on its face if you're a gear to high.

I'd replace the reeds. Also, check to see if the power valve is carboned up.

Reeds are between the carb and jug.
power valve is in the jug in the exhaust port.

Haha ! Bringing out the crazy frog Axle huh ? The original :
https://www.youtube.com/watch?v=Vju2pyqXBLg&feature=youtu.be