Hi folks. just picked up a nice 74 DT360. 2200 miles and nearly survivor condition. cleaned the carb and petcock and she fired right up. idle is high with idle screw all the way out and carb barrel bottomed out. with it running a partial block of the air and it idles down. I sprayed carb cleaner around the intake boot with nor discernible charge. Im thinking mag side crank seal. any opinions? I’d love to hear them. 
 

Mag seal possibly but theyre pretty robust on those.
My thoughts are is the choke jet in the bowl blocked & if you have the choke open which opens an airway bypassing the slide it'll take the revs up.
Bowl jet is fixed & a poke clean jobby with something small & it gets dirt gets under there too from how it feeds from the bowl to under the jet.
Think there's a small hole in the extended tube that reaches down there but never had that blockup but worth looking at.
Idle mixture on the angle is screwed in for rich.
But even if the idle jet was blocked it's still shut down--& stop.
I might be wrong of course.
One more, i've been making up carbs out of bits n pieces & had occasions where the emulsion tube extension sat too high & stops the slide hitting fully down--could see air under it looking through in the light & was all it took.

Make sure front motor mount bolt is tight...  if not, tighten it and see if it gets better.  If tight, loosen it and see if it gets worse.

I've worked on 2 DT360's with air leaks and on both it was the cases leaking into the front mount.  Both had loose mount bolts.

Both of those leaks were found by pressure testing.  Especially with the price and availability of the correct seals, I would pressure test and not guess.

Thanks Mark, I’ll try your suggestion. Amazing the difference between the DT and the RT. I took both for a short ride yesterday. the RT is definitely louder and feels quicker but the DT seems like it has more range. The exhaust also smells different like you can smell the gas in one and the oil in the other. I might like  riding the RT a little better. 

thanks RT. all great suggestions. I did the berryman dip and sonic clean with all passages confirmed clear. the slide was pretty mangled and may be letting more air slip around it. almost looks looks like someone sanded it…poorly or put it on a grinder. I don’t know how critical the tolerances are but perhaps I’ll replace it just to be certain, 

The slide fit is pretty important and if there's significant air passing by the slide it's the same as if it was raised up with the idle adjust screw. I think I'd look at that as my #1 suspect then work on the others suggested.

Has some clever guy machined the carb larger & gone too far leaving a slight gap at the sides of the slide.

If you don't have the air filter/cleaner attached it will run lean/idle high..