Carb Issues 1978 SR

Recently rebuilt my carbs, with new manifold boots. Only OEM replacement parts, ultrasonically cleaned with K&N Filters. The bike was initially sync'd, and settled down to an idle pretty well. The problem I am having is that once rev'd up, it does not want to return to idle. It lingers for a long period of time at high RPM, and very very slowly over time returns to idle. I tried a number of different fuel mixture settings with no improvement. Any idea what could be happening here?

That means lean.  Either base jetting, or the intake boots are leaking false air.

Pod filters totally mess up the jetting.  There are thousands of posts here detailing out this situation.  

Thanks, I will try a richer fuel adjustment setting
 

First question I have is it a D1 or a D1a, as they have different size carbs on basically the same bike. The D1 came stock with vm24ss carbs and the D1a with vm22ss carbs. They have different jetting and slide cutaways, The 24s have only an air screw and the 22s have only a pilot screw (sometimes called a fuel screw). Tell us some more about your machine, 

Also be sure that the throttle cables are properly lubricated, adjusted, routed and not frayed or damaged. Any drag in them can cause the carburetors to return to idle slowly or not at all.

Yes, I am sure the throttle cables are working correctly.

Again tell us more about your machine. You indicate you have new filters. Does this indicate more than one, as in pods? If it has had pods in the post how did it run?

The bike is a 1978 D1 SR, 26mm slide carbs, with the air adjustment screws easily accessible on the side of the carb bodies. All 4 carbs have a separate K&N Pad filter. I purchased this D1 from Washington state and it did not come with the airbox. Stock Jetting which is 102.5.

Based on feedback for the runaway RPM condition, I took the crab set off and inspected the new intake boots. It was clearly leaking fuel thru the interface on the #3 and #4 carbs. I found that my cylinder head was not completely flat at that interface, so I took care of that. The boots look like they needed a bit of care to enure they were flat across the rubber surface.

I will provide an update once I have the carbs mounted up and run the system again.

I got everything back together and running stable. It idles really smooth now, but still has the runaway RPM issue? Not sure what is going on here.

Still searching a solution to this issue. Clearly there is an air leak in the carbs somewhere. I have ordered some new (again) chock circuit o-rings and rubber plunger cap. I understand there are a couple different length fuel air mixture screws, 13 vs a 16mm? I had a suggestion to RTV the base of the sync nipple ports just to make sure they are not leaking there. There is a gremlin here lurking.
 

I pretty much guarantee your issue is you have an air leak on the carb to head rubbers. Both the seal to the head, the clips on the carbs and the vacuum takeoff tubes have to be air tight. 
If you've already sorted the rubber to head joints you need to make sure the carb to rubber head intake clips are tight. Nipped up is not tight enough. 
You also need to ensure the vacuum ports on the intake rubbers are capped and airtight. If they are repop or old cap rubbers you may need to add clips to get them to seal. 
Lastly if you have a vacuum fuel tap ensure that both ends of the vacuum pipe is also airtight on their spigots. Add clips if nessescary. If you have a gravity fuel tap which doesn't require vacuum to operate but you do have a carb rack that has a vac tap spigot this MUST be capped and air tight.

I do have a vacuum actuated petcock. It is possible that they air leak is there. I had not thought of that possibility. Thanks for that input.

I have new OEM Air boots to carbs and clamps. Seems like they are all snugging down well, but it is possible that this also the issue. I sprayed carb cleaner around the boots, but the idle did not increase. I have the old boots and clamps, so I could refit to see if they resolve the issue.

Thanks for that feedback.