Hi there my ongoing issues with my dt400mx have resulted in my purchase of a Rex’s speed shop 12v conversion and ign upgrade  I have to say it all fits really well and the instructions spot on . But I now have another problem after fitting it all I turned the fuel on and it looks like the float needle stuck and it’s badly flooded the engine. How can I dry it out it refuses to start and the plug is soaking every time I try to start it. 

Just be sure there's no spark happening & push it around the yard with the plug out. It'll make a mess but will wash off. Maybe drop the exhaust but just a bit of a pain to do. Or could pull the reed valve & suction it out. I go for easy--plug out. Leave fuel off of course, right to the point of starting, or see if it will start then turn fuel on. These old girls need a drain bung on the case like I think Villiers had in the early days.

Another option I perfected as a kid (as my LT2 flooded regularly if I forgot to turn off the petcock) is to remove the fuel tank and spark plug, piston at BDC or very close to it, lay the bike on its side and then slowly flip the bike upside down.  

Best to lay your model down on the right side so any fuel the got into the pipe can also escape.

Important to put the piston at BDC *before* flipping it over.  Let it sit a bit.  If you were at BDC and flipped the bike slowly, 99% of the fuel will drain out the plug hole.

Fuel tank removal is optional, mostly to prevent damage and gas leakage from cap.

Last time i flipped my bike upsidedown during covid time i ended up in hospital with a broken back. Mind you i was riding it at the time haha. Sorry, had to write something stupid didn't i.
I guess you'd better address the cause of the flooding too, or turn the fuel off each stop in the mean time.