"Our factory manufacture various of carburetor"
Runtong is a Dellorto SHA "shaped" carburetor (the word clone would be insulting). It features a 15mm bore and a lever choke. The float bowl and top cap are both made of fairly low grade plastic. These can be found on eBay for as low as $11 shipped from Hong Kong. It uses a single brass jet which is un-marked. The carb does not come with any air cleaner, or air box.
First off, the choke might not work (mine was defective). Remove and throw away the bent up auto-release. Stretch out the choke return spring a bit and re-install it on the choke pivot screw (do not hook it to the choke lever) to create an interference fit. This will allow you to set the choke lever in any position you like.
The main jet is a mysterious beast. At first glance, it looks like a typical Dellorto 5mm, but it isn't. It's 6 x 1.00mm. This is not the same as Dellorto 6mm jets which are a finer thread. You will need a large Bing jet of your choice, the Bing jets will screw right in. You can also run an M6-1.00 die over a 6mm Dellorto jet. Clamp the die gently into a vice and find a short handle screwdriver that fits the jet snugly. Carefully twist the jet into the die to cut the correct threads in it. It comes out looking surprisingly clean considering you are cutting threads into other threads. Twist it in and out of the die a few times to clean it up then use a brush and carb cleaner to remove the brass filings.
In general the seals are the weakest part of this carburetor. The float bowl has a flat seal rather than an O-ring, what's worse is that it tends to shrink. The banjo screen is badly distorted from the factory and uses two flat rubber seals to fill the gaps, these seals will tear if the banjo is moved too many times, they may also crack on there own, so watch for leaks. Lastly, the rubber tip on the float needle may not hold up well under vibration and can wear quickly causing more fuel leaks.
Yes, you got what you paid for. But, you can make it work!
Link to the large bing jets, as I dont know how to link it straight into the words "large Bing jets" If someone can do that for me... Link: http://www.treatland.tv/large-bing-jets-p/bing-jets-large.htm