Modern Vespa

20/20 carb?

Your sealed idle jet is for the older carbs, that had a separate/fixed air corrector.
The 20/20 uses a pilot jet with the air corrector, atomizer and fuel jet in one integrated bit.

What filter are you using?

The trick to finding the right main jet is *knowing* what's too rich. You want to be just lean from there for maximum power and coolest running.

120 might be adequate, but if you tried it, you might find that 122 or 125 were better.

If you're not going to ensure you know you're on the correct main (and even if you are), run a CHT so you'll have some warning before you seize it on the road.

You may find that even at extended WOT you never get into dangerous temps, but you may also see that your temps start creeping up and know it's time to cool things off a little.

Its a 20/20 [second hand no history but as new] with a stock air filter. the air/atomizer/main are seperate items. I will give it a run round the block today.

I have a 122 and a 124 coming in todays post...

The scoot won't tick over with the 40-100 idle jet. Seems to run rich with the 42 [sealed jet] you can see from the pic that the hole next to the idle jet is sealed with a brass bung.

What jets did you end up using on your b177 kt?

I'm surprised it runs with no air correction
Have you adjusted (retarded) ignition advance for the kit?
Should be 18 (maybe 20 with points) vs original 28.

Not something you want to hear, but that grade carb can frustrate the hell out of you. For one, they aren't cleaned/inspected at the factory. Put that in an ultrasonic bath and you'll be surprised what comes out of it.
The SI is also relies on precise channels and things fitting that that carb doesn't have.
Pinasco made/makes a PNP carb specifically for the 2 port Pinasco on a VBB. Let me look for one on Ebay...

Found one. It has a fixed 1mm (=100ac) air corrector
https://www.ebay.com/itm/145119810776?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&mkscid=101&itemid=145119810776&targetid=1645685073288&device=c&mktype=pla&googleloc=9030955&poi=&campaignid=20133407470&mkgroupid=147476396765&rlsatarget=pla-1645685073288&abcId=9312979&merchantid=131376593&gad_source=1&gclid=Cj0KCQiAz8GuBhCxARIsAOpzk8zR25UnFbkmOYRe_-M4z2V6dF3shEhJuWnlZRBJKvAWeF6_aLQcqTsaAmycEALw_wcB

My notes from when I was going to kit my 2 port VBC 150, 20/20 carb:
148/160, 55/160, 52/140 pilot jet.
160/BE3/105-115 mj set.
Piaggio (tan color mesh vs blue) un-drilled filter.

Ah...I'm in the UK...I've haven't tried altering the timing yet, I can look at that over the next few days. The main jet holder is the diffuser[BE3]/air bleed[140] with a 120 main jet. I'll have a look at it tomorrow.

I have the 2 port Pinasco177 kit. I've flowed the passage from the carb to the engine vase when I rebuilt it.

Below is the jetting sequence I went through...

I'm looking at main:120 diffuser:BE3/140 pilot:55/160 but the pilot seems too rich [the mixture screw in only 1/2 out], I'm gonna buy a 40/120 and try that. The weather is shit here in the UK so I can't get out for a good run!

Did you adjust the ignition advance?

Not yet. The Pinasco instructions do not mention timing changes.