The PURGE bulb draws air , then fuel out of the carb and returns it to the fuel tank, which is pressurised to around 7 psi.
In order to do this it has a check valve ( some times 2 ) so the air & fuel can only go one way, from the carb to the tank.
If yours is blowing bubbles then chances are the check valve is not working and air is being pushed back from the tank through the purge bulb and then most likely through the carb.
Some carbs also have check valves in them some don't.When you take the bulb off that little brass bit is a check valve.
When I first started the carb rebuild kits would have check valves in them and the repair tool kit came with punches to remove & replace them.
Now day the carb gets tossed.
You can order in the base ( metering chamber housing ) that has the check valve in it but generally it is more expensive than the replacement carb
Walbro have a wonderful web site with pretty pictures & diagram showing exactly how carb cabs work & where all the bits are so if you really want to know then search for it.
The manuals & even videos have a link in the bottom right hand corner of the page where they are hard to notice .
And before you tell me it is a Zama / Ruixing or Wing Foo, they all work exactly the same regardless of the brand and in fact, a lot of parts are interchangable between brands.
Two types of cube carbs, butterfly throttle & rotary throttle, the brand name means nothing.
