Modern Vespa

I have A 1960 VBB with a 1980 PX125E engine swap. Engine was running fine, carb was cleaned and rebuilt, and there was even power throughout the RPM range, while riding around on some backroads, I ran out of gas and had my friend come to the rescue, he showed up with a can of 50:1 trufuel gas from home depot, it got the scoot home, but now, even on 87oct 50:1, the engine has a dip in power around 1/4 throttle, and if I hold the throttle there then it kills the engine; It is currently running a SI 20/20 carb, and a Simoni exhaust. I'm wondering if a carb upgrade (either a 24/24 or a 20/20 upjet) may fix the issue?
Inspecting the sparkplug shows a dark-mid brown, and there is no power loss when the choke is at 1/2 or more.

Carb prob pulled some junk in from the bottom of the tank. Try a quick carb clean by cleaning the bowl and screen and then clean out the jets and passage ways. Don't really need to remove carb to do that but need a can of carb cleaner. Try that and let us know what results you get.

Gunk in jets

So i took the carb off and cleaned out the bowl and all the jets, and replaced all the gaskets, but it still has the same problem when the engine is warmed up, is there anything else it could be? I don't know how to tell if its because the engine is leaning out or flooding, still new to carbs.

Gunk in jets.
If you look in the end of the pilot jet, there is a very tiny hole. Poke a fine wire through it.

Just took the jets out and shined a light through them to see any debris, they were all clean so i put them back in and took the scoot out for a short stint, there was wired power loss under load still but when i had the choke pulled out it ran just fine. I should also mention that I read somewhere that there are "default" adjustments to the idle mixture screw and was wondering if that could be a part of the issue.

If it ran fine prior to running out of gas, then I would assume the settings on the carb are fine. I suspect you have a fuel restriction in the fuel delivery system caused by sucking in debris when you ran out of gas. Find yourself an old plastic lawnmower or snow blower fuel tank and rig it up on the back rack and run the fuel line to the carb. Fill the mower tank with 2% mixed fuel and take a ride on a level road. If it runs good with that set up then its your fuel delivery system. If it runs the same then its in the carb (Jets Clogged).

My two cents.

Hec

Not sure you understand. The pilot jet end hole can't be shone through with a light. Need to poke it.

^^^^^^^

$10, problem solved.

https://www.amazon.com/HIFROM-Carburetor-Cleaner-cleaning-Motorcycle/dp/B06XXSVGBW

Of spray Start-Ya-Bastard into the end of it & check it comes evenly out the holes at side.
Holdingthem up to the sun is a great way to look thru the jet hole

Tried poking a wire through the jets to clean them, then I used cotton swabs and gasoline to clean the crap out of the carb bowl and the float chamber, I also replaced the float and needle. After messing with the idle mixture screw, nothing changed. After messing around on the bike to try and see what's wrong, I noticed that it just gets bogged down around 1/8 throttle and even does it when there isn't any load on the engine, just holding it at 1/8 will kill the engine. Still works just fine when the choke is pulled out.

Blast these channels(in yellow) using the red tube of your carb cleaner.

In that diagram, the filter screen above the sediment bowl is doing nothing. The mix actually goes up through it and down the tube into the bowl.

If had to clean crap in the carb bowl, maybe stuff in your tank and in fuel line, too. May need to do more then just the clean carb.

It's a schematic.