carburetor question?

on my Qingqi QM50QT-6A
which is a 49cc moped...
-the carburetor is got me stomped.
-i know that the throttle controls the air-flow via butter-fly.
-but there is a vacuum diaphragm in the center of the carburetor that controls the needle/fuel flow.

-on the filter side of the carb is a port that controls the lift on the needle and diaphragm.

-however this port needs positive pressure to lift the needle but i cant see how any pressure could build up to lift the needle being that there is only negative pressure or vacuum throughout the intake system?
kinda hard to explain but i hope that paints a picture...

can someone please explain how this carb works....thanks

from this pdf , the doemstic QM50QT-6 series comes w/ PD18J carb (a carb that commonly on Kymco 50cc)

Ahhh.. the mysteries of carbs never ends! Check out the following site for a good walk through on how CV Carbs work. The section called "Main System - The Meat" near the bottom of the page discusses how the diaphragm and pressure balances work.
http://faq.ninja250.org/wiki/How_a_c...arbs_explained

Also, along with Humanbeing's suggestion, if your carb is old, broken or worn out, you may be able to replace the whole thing for not too much money. Doesn't hurt to have two carbs, one so you can ride, and the other so you can clean and explore how it works.

CC

hi guys apology for making this thread alive again had a problem with my carb I got myself a new service kit for my toyota carburetor, and did everything by the book, I serviced the carburetor, replaced needles, seals, ball, jet, valve and so on, till the time I was about to install it back on the engine. The gasket appears to be wrong. Have a look at the picture. and tell me what you think. engine does not start when I install it. I am thinking the gasket is blocking something. anyone seen this before? please help. thanks a lot!


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