[Broken] Scooter starts after carb drained but lurches and stops on test run

Hey helpful people,

I've got a Chinese scoot which used to work. It started lurching when I rode it. By that I mean as soon as I hit a certain speed the engine would hick-up causing the bike to slow down and then lurch forward. I would also have to release the throttle a little bit to avoid it hiccuping.

Fast forward a little, the scooter won't start. I cleaned out the carburetor and the scooter started and idled fine. When I took it on a test ride the lurching started about a minute in, at a very low speed, and then the engine turned off completely and it wouldn't start up. I drained the fuel from the carburetor and got the scooter to start again but had the same problem again. I thought the carburetor might be flooding or something because whenever I drained the fuel out it owed start up again. I tried adjusting the float, but still had the same problem. I bought a new carburetor in hopes that would fix it, but nope still same problem.

Any suggestions are much appreciated.

 

An air leak on the inlet manifold would be my guess. At higher speeds the leak will weaken the mixture causing the 'hiccuping'. It could also be ignition timing being off or wrong valve clearances (I'm assuming that this is a four stroke bike).

 

Oiled up plug?

 

I looked for an air leak and didn't find one. I tried using some water to see possible small holes I was missing. Would an air leak on the inlet manifold cause the scooter to no longer start until the carburetor was drained?

 

What colour is the centre insulator of the spark plug? Does this carburettor have an automatic choke fitted? Also, is this bike a 2-stroke or a 4-stroke?

If it's a 4-stroke, the clone Keihin diaphragm carburettors are troublesome.

 

Has it got the std airbox on it? water ingress is a problem on some Chinese scooters, water being denser than petrol it all way's lay's on the bottom of tank then into carb, drain petrol off and see if there's water droplets in the petrol. Petrol just soak's away where water stay's in droplets so easy to see.