the cylinder appears to have the cross hatch pattern from being honed. the piston however does not look good. you can pull the cylinder and polish the scoring out but if the grooves are too deep,it would be better if the piston was replaced with a new one of the same size.

What is the white 90 for, above the idle screw. Its broken. Is it just a vent?
And after cleaning the float needle and seat real good it still pours fuel out wtf!

I am pretty sure it is just the vent. Does the carb overflow out the overflow tube at bottom of carb.

Yup out that brown hose you see

that broken elbow is just a vent,it is usually the vent that's lower on the carb on the other side that leaks fuel when flooding.

So its no problem that white vent is broken off?
Ya it wont stop pouring out the vent 9n the other side and out that brown hose on bottom of picture

you measure the float arm on the carb,the distance between the float arm and carb body with the float arm at rest when setting the float height.

not a real problem as far as functionality goes on the vent.

I did. To 22mm carb upside down straight edge on gasket surfaceto where the floats contact arm. Is that right

it sounds right,I am not so sure on the specs for the 1977 DT400.

on some of the older carbs,that is the spec.

at this point,if you replaced the needle and seat in the carb,I would suspect the floats themselves no longer float in the fuel. this will cause flooding.

you can see if the needle and seat leaks. remove the float bowl and attach the fuel line,then turn the fuel on,raise up on the float arm with light pressure,it should stop the fuel flowing and not even drip.

another question I must ask,are you turning off the fuel when parking the bike with the engine off? they will flood for sure if sitting for a very long period with the fuel left on and with the engine off.