Thanks Msavitt, still hoping to get the surging issue sorted out. I'm gonna keep pecking away at it. Call me an old fool but I'm not convinced it's not fixable. I have a wild hunch it's starving for fuel at low to no load conditions and if that's the problem then there should be a work-around, or not, but it won't hurt to try a few things before giving up.

I'm gonna pull the carb again and reclean everything, (for the third time), paying particular attention to the pilot jet and tunnels that feed into it. Those are mighty small passageways and wouldn't take more than a speck of dust to clog things up. Worth a try anyway.

If cleaning doesn't do any good my next plan is to go up one size on the pilot jet and see what happens. I love riding this bike more than any other that I have now or have ever had and I just want it right, stubborn streak in me won't let me quit on it.

Jack - I will try to record my chug chug chug and post it.

Mine idles nice, runs strong, buzzes like mad at 6K, doesn't knock or ping, but does that chug chug thing at light and steady loads. 

Getting everything dialed in and air tight certainly helped to minimize this phenomena and a 2nd meltdown, but based on what several experts have stated I have accepted this as an inherent characteristic of this now ancient bike and have learned to enjoy the sound and associated jerking.  I weight in at a svelte 250# and even when riding hard on a 100F day I have no issues, so I am at peace!

Jack, just curious if you found OEM crank seals or went with aftermarket ebay ones?

If you went with aftermarket, might try a pressure and vacuum test to make sure seals aren't leaking under vacuum.

Look forward to your video to see if we are even talking about the same thing. I think we are but a video would verify it.
I pulled the carb this morning, went all through it one more time and everythings clean as a whistle, already was it turns out, just wanted to totally rule that out. Took a good long ride right afterwards and couldn't see any changes from yesterday.

Just ordered a 52.5 pilot jet just for fun and will stick that in there when it gets here. Probably won't make a bit of difference but it's only 8 bucks. Will post my results whatever they are.

I'm having a great time riding it quirks and all and I'm not argueing with the experts, just satisfying my own curiosity. I find it so hard to believe I wouldn't remember this bike acting up like this back then, or that I wouldn't have noticed it. All my memories of this bike are positive up until the day I parked it. Anyway, I'm having fun piddling with it and getting quite an education in the process so it's all good!

Mark, I got OEM seals from Enduronut so hopefully it's not them.

The jerkiness is at it's worst when I close the throttle completely, almost violent at that time, and the only way to make it stop is to either pull in the clutch lever or get back on the throttle. 

A question for you; would the vacuum or negative pressure, whatever you want to call it, would that increase, decrease, or stay the same when closing the throttle at speed? 

I think we rebuilt the motors about the same time.  I am having the same problem and I don't remember it being this bad back in the day but I don't ride it like I did.  The temperature on my bike is like yours the highest it has been is about 360 degrees and the bike runs the best when temp gets above 300 degrees.    I have 90 miles on the new motor.

"I am having the same problem and I don't remember it being this bad back in the day but I don't ride it like I did."

Exactly the same here. I could have written your entire post except for the milage. You're a bit ahead of me on miles. I was only running it for very short periods for quite awhile cause I thought it was overheating, But I finally got a trail tech temp gauge and have been riding it for longer periods now so will be putting more miles on from here on out.

I'm pretty sure I remember reading about a few DT 360s that didn't have this problem but can't remember where I read it or even if I really did. But definitly seems to be pretty common with them even if it doesn't effect every single one. For all I know maybe what's left of my brain is blocking out the quirky jerky thing from years gone by and only remembering the good parts. ( :

I'm gonna keep experimenting anyway, ya never know, might get lucky.

I got a shock when I got my MG1T running a few years ago.  I had one just like it as a kid.  I remember it as being a rocketship that went really, really fast!

Yeah.  Not so much.  It's kinda quick but not very fast at all by modern standards.

I also was looking for an old El Camino because I thought they were the coolest vehicle ever made...  Who wouldn't love a nice little car/truck?  (Or ute as I think they call them down under.)  Perfect vehicle! 

The old Chevys are stupid expensive for junk so I got a nice Ranchero a couple years ago that is an older show car that needs some TLC.  OMG did I forget what a pain carbs and chokes are on a cold day!   We are so spoiled by fuel injection and computer controls.  I kinda remember having to warm up the engine before driving off on a cold morning when I was a kid.  The Ranchero is actually in pretty good shape but I just forgot about pumping the pedal just right before turning the key and having to drive careful until it was warm or it might cough and stall.  It seems to run like crap when cold but we've forgotten that's "normal" for a 70's car.

So it very well could be a combo of your original bike not having as much an issue and forgetting bikes and engines didn't run like sewing machines back then.

Yes Jack the water base paint is hard work. It's funny as no matter how good you get the finish there's always something . A man on a flying horse isn't going to notice it anyhow Jack . It's only you that's noticing it .
Main thing is your up and out on it .
I'm having trouble with my 360. Actually it's never been right and i've just started looking into it. Mine is misfiring when you open the throttle quick and only happy when your accelerating smoothly up to around 50 MPH . I think modern fuel isn't helping neither is the shape of the combustion chamber or plug position.
All been interesting reading so far Jack. Glad to see you've sort of got there in the long run. 

Jack -
here’s hopefully a link to the worst video ever. I cannot be responsible if you stare too long and have a seizure.  The voice over sucks once I get rolling. Besides the local fauna the only think I am commenting on is the chug chug four stroking on the no load steady speed sections.