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I was beginning to wonder if the problem wasn't the pilot jetting but a function of porting, pipes, compression, the way it had been tuned.
The best pilot jet still doesn't make it run very well, it doesn't sound or feel right until the throttle is opened to just past quarter, probably of little concern on the racetrack.
I have ridden it "on or off" no throttle or quarter throttle. Any danger of starving the top end of oil riding it like this?
I'll look into those UFO inserts,

Well, I tried a whole variety of pilot jets from 17.5 to 45 and throttle slides 2.5 and 2.0.
I tested it on an incline right outside my house and all at less than quarter throttle, the zone where it does not run well.
I think I could hear it knocking on the 17.5 and the 45 was super smoky and bogged down maybe 27.5 was the best, but none of these settings, cured it of its unhappiness at less than quarter throttle.
I don't think it's pilot jet size. I've thoroughly cleaned the carburetor and there are two orifices that are fed by the jet and they are clear.
Once I'm past quarter throttle (I calibrated the twist grip) it seems to be running fine (there may well be some fine adjustment to be made there but nothing like below quarter)
I have posted Engine and carburetor details elsewhere but as a quick recap, it's an aggressively ported 350 with 34 mm mikunis, 152lbs compression and 100 octane gasoline. It was a race bike that came to me, and I saw fit too resurrect it and put it on the road. Steep learning curve in regards to jetting and tuning and I really appreciate this forum!

Ok, a couple of things,
I asked AI about what's going on with my carburetion and it suggested that my slide at 2.5 was a little big and that 2.0 might be more appropriate. The idea being too much air was flowing initially and a smaller pilot jet couldn't keep up. If you didn't want to buy two new slides go up pilot jet size.
Again that's what AI said, what do you think?
I'm about to make a trip over to a bike shop and see if they have any larger pilots. If not, I have to buy them online. Can I buy Chinese? I can certainly get a large selection for a lot less money.
I see online that correct float height is 24 mm from the body of the carburetor to the top of the brass pivot that the floats engage on. Is that correct?
The afore mentioned brass pivot is held in with a pin that is peened over on one end. I've tried tapping it out to remove the float needle assembly but it doesn't want to move. Is there a trick?

Well, maybe I do?
I switched to a 32.5 pilot and dropped the needle one (now all the way down)
and experimented with the air screw.
I also adjusted the throttle slides and idle stops as best as I could. It's best at 1 3/4 out (air screw)
It starts right up and idles fine but put a load on it as you pull away (and (I'm going to try to use words) it sounds like it's four stroking (?) the exhaust tone is sharper, almost a clack sound (way too lean?)in the chamber. That scenario when pulling away on an incline. A lighter load less severe.
Perhaps the idle circuits are slightly gummed up but would it start and idle the way it does if they were)
I did blast brake cleaner through them. Perhaps I should put them in a ultrasonic cleaner?

Main jets  300
Pilot jets 32.5
Needle jet .158 P-8
Slide      2.5
Needle     6F8 (clip in top groove)

Appreciate your consideration!

I'll make some adjustments and report back. Thanks guys.

Pictures of round mirror, square mirror and no mirror, the latter looking the best for sure but I can hardly turn my neck these days and so need a mirror of some kind. Can you actually see anything in those little bar end mirrors?

I tried screwing the idle screws in, it bogged the motor down and no improvement.
Not sure how to measure what needle I have or needle jet or slide cut out?
I included a picture of the carburetor, main jet removed, next piece of brass in is slotted and engages on a pin to prevent rotating, I'm going to guess that is access to the needle jet, but not sure how it removes.   
Also a picture of the spark plugs. That's 10 minutes, running up and down the road at idle throttle setting adjusting the air screw.
There's about 10 miles in total on those plugs. They're very oily.
Running 36 to 1 premix.
The reason for the 100 octane Ave gas is 155 pounds per square inch pressure in the cylinders and lots of porting and squish band. M in sc says use 93 and as I gain courage and confidence, I might well do that but for now, I'm not too confident.

Ok, i'll try that today.
And for a point of reference, I'll find out what needles and needle jets I have. Is the needle marked in someway or measured?
Thanks for all your replies, I really appreciate it.

I'll try one turn out or even less. It's always been in my head that you started one and a half turns out and anything less would be too lean.
I'll try 93 octane too, if it knocks will I hear it above all the other noise? Is there some other way to check for pre ignition?

So I've just about finished this RD 350 project which I've spoken about here a couple of times and just put some pictures in the project section.
It starts up first kick and idles nicely but at a small throttle opening as you pull away, the Engine sounds to my non-expert ear, lean, As you open the throttle, there is a definite switch to running properly (?)
This is all happening with the air screws one and a half turns out. If I increase that to 2 1/2 turns out it improves it slightly, but that transition as the throttle is opened, isn't as smooth.
The carburetors which are 34mm Mikunis have,
300 main jets
35 pilot jets
The needle is in the second groove from the top.
I have a large selection of main jets, but only 35 and 32.5 pilots.
I'm tempted as a first measure to put the carburetors in the ultrasonic cleaner as the circuits maybe gummed up but the fact it starts so well and idles makes me think that's not it.
Suggestions?

After mini an hour, it's just about done, save a little carburetor, tuning, and getting the electric speedo working.
As I had posted here before, it was a race bike and it had been ported, 34mm carbs, high compression, etc., etc.
It's got 100 octane aviation gas in it and I've set the timing at 1.7mm btdc.
I was expecting it to be rather unmanageable, but it idles and goes through the gears quite nicely below 6000 RPM, certainly keeps up with traffic. Above six grand however it's a beast! can't really define its performance scientifically but anxiety to shit eating grin might cover it.
I was told it had ran on 110 octane race gas, but I didn't want to go there hence the aviation gas and the slight retard in timing. I can't detect it knocking but everything is so metallic and loud I'm not sure I could. I did get some wrong gas in a Buell one time and you could make that knock and it was quite apparent.
I am having some issues with the idle circuit in the carbs, I'll bring that up in the turning wrenches section.
Here's some pictures, perhaps not the best from a Cell Phone, a couple from before.

Probably a UK gallon as well :)

Ok, that's what I'll do, 93 and keep an ear out,
Thanks

So to recap, this Engine has an extreme porting job and a rather unusual squish band? It probably won't make any power until 6000 or so and I will quickly tire of it on the street and I'll be looking for another top end suitable for the street? I can lower the cylinder pressure with new heads, but that still doesn't deal with the aggressive porting.

But I do have the bike with the engine that it has for now. I didn't build it as it is, it just came to me and I couldn't say no, always regretted having sold my RD 400 a few years ago. I've been working hard, cleaning it up and changing a few details, it had been sitting for about 10 years collecting dust and light oxidation and I am going to ride it as it is even if it's just once or twice. I'd rather not buy a 5 gallon pail of race gas, but I will if I have to. I guess I feel a little nervous putting 93 octane in it, if I were to then would the only way to tell if it was OK was the audible sound of pre ignition, right around without my helmet on with my good ear turned towards the bike, or is there a better way?

How about some 100 octane low lead Av gas. I can get it locally and it wouldn't be a permanent solution to the aggressive tune of the bike, that would be a new top end which would be a project for the coming winter.

Thanks for your replies, I appreciate your help and admire your accumulated knowledge

I've collected some measurements of this motor of mine for your consideration. I drew the exhaust ports out the same way as vintagewannabe's clymer modification post and included them as a photo, which I hope is legible.
I've also included a picture of the carbon deposits on the piston crowns, which I thought looked interesting, something to do with the way the fuel burns and the squish band?
There's also pictures of the cylinder heads showing tiny pits which are perhaps something to do with preignition? They are on the forward half of the head on the centerline closer to the exhaust port on one side and closer to the plug on the other. These pictures also show what might be someone's initials? And some information about volume?
When I cleaned the pistons, there was only one pit on one and about five on the other again closer to the exhaust board.
There are oversize read cages with a spacer to fit them and greenish FRP read valves, Boyson's?
32mm Mikuni carburetors with a 300 main jet.
Moto Carrera millennial expansion chambers.
Ignition timing set at 1.8mm btdc.
The Squish band clearance measures 1.47mm at the outer edge and 1.74mm at the inner (measured with lead solder over the gudgeon pin)
I measured cylinder pressure with two gauges and a cold engine,
161lbs left and 155lbs right. The other gauge read 10lbs less. Both gauges were older, Taiwanese, and had schrader valves in the plug adapter.

This all started with me wondering whether I needed to run this on 110 octane and I think I know the answer, but I would be interested in what you have to say.