Modern Vespa

Hi guys! I need your help with a problem that is driving me crazy. After investing multiple hours, I'm able to provide a good description of the problem.

- The engine starts nice
- Idle is good and it doesn't stall
- Full power is good, nice speed, no problem

- The problem is when I use the throttle anywhere between 1/4 and 3/4 of the power. I immediately lose 100% of power, it feels like the engine is not getting enough fuel

- Situation 1: I'm at a traffic light, and if I start at full gas, everything works perfect
- Situation 2: I'm at a traffic light, and if I start at 30%/50% of gas, the engine loses all it's power and stalls (I immediately release the throttle to avoid stalling)
- Situation 3: I'm at full throttle, everything works fine. I want to reduce speed and let's say I go to 60% throttle. The engine works fine for 3 seconds, then it loses all its power (almost no sound) for 3 seconds, then it catches power again for another 3 seconds and so on.

Note that when I say that the engine loses it's power, it really does. Absolutely no power to move it 1 inch forward. You can barely hear the engine... super weird.

These are the checks I did:
- Fuel tap works fine
- Remove the carb and cleaned it (maybe I didn't clean it enough)
- Adjusted throttle needle
- Checked air filter/air intake for obstructions

I know there is a fuel jet that is responsible exactly from 1/4 to 3/4 of throttle. Could this be the problem?

This situation is driving me really crazy. Do you have any hypothesis on what could be driving such a weird situation?

Your help is highly appreciated!

My ET2 carburetor knowledge is pretty rusty. Its been years since I've cleaned one. I'm going off of basic CV carb theory here. Normally theres a starting jet (on the outside of the carburetor), the idle (in the bowl off to a side) and the main jet stack/ needle (in the bowl, dead center). Does this theory match what you saw?

Did you remove all 3 jets and clean the jets and the passages with carb cleaner/ compressed air?

You said you adjusted the needle. What did you do? Raise the clip or lower the clip on the needle?

I adjusted it down, to make mix richer. Counting from the top, I moved it from the 2nd to the 3rd position (now it's in the middle... 3 out of 5)

Do you recall any changes to the carb/ engine that happened before you lost power? Engine seize? Strange noise? Scooter sat for a while? Main jet changed? Weather was extremely cold? Anything?

Did raising the needle make things better or worse? If it made it better, youre running lean and it needs the extra fuel to compensate. Compensate for what? Youre going to have to poke around and tell us.

Since its a two stroke, did you look for air leaks? Is the paper gasket in the top of the carb where the throttle cable attaches to the needle? Did you remove all 3 jets and confirm theres nothing clogging them? Did you clean out the passages with carb cleaner/ compressed air? Whats the condition of your reed petals?

Lots of questions.

I've seen this a few times. They're old and they do wear out.
Make sure you still have an air filter, and it hasn't been partially sucked into the engine.
If it's a Weber carb, about all you can do that works is switch to the DellOrto. After you are about 1/4 throttle, you are into the main jet.

any solutions? I have the same problem. I know the best thing is to swap carbs. that's not an option for me. im gonna try and clean carb again and make sure im getting good fuel.

thanks