I am the proud owner of a 77 dt250. Ground up. All seals replaced in the engine. Wiesco 1mm over piston and rings. Boyensen reed valves. New points and condensor. Spent countless hours getting the timing right. It has a horrible mid range miss. Plug is dark black carbon. Stock jetting in carb. Float is set correctly. Starts like a champ first kick. Excellent compression. Dialed the injection pump back a little from factory recommended. Using Mobil 1 synthetic 2 cycle. Any thoughts? Some smoking at idle. Not a fogging but noticeable. Just sputters at a steady throttle.

Did you have trouble with the points that it took a while? Maybe the gap is out?

Jets ok in the carby as well as the jet needle on the right notch?

If you changed the reeds that might have something to do with it.

Exhaust is clear?

Miss always makes me thunk ignition - coil, lead, plug, points

Hope that helps

carb jet needle set too high?

Took a long time to get the opening point of the points just right. Made a wire with a horseshoe connected. Disconnected the wire at the points. Connected it there and the other lead for the test light to ground. This eliminated the light dimming thing. It was either on or off. Turned the magneto with a ratchet. That way no flex on the mag. I noticed that doing it by hand could change the reading significantly. Been reading up on the Mobil 2t. Thinking the injection level is too high.

JR