fuel-vacuum hose diagrams for QMB139 By dubyajayes (Read 26,907 times)

[dubyajayes]

I have a 2008 Shanghai-Shenke 50cc scooter that I can't get to run. I've replaced the carburetor (CVK type), ignition coil and spark plug, still no go. The spark appears weak but there is spark. Fuel flow to the carb is good, yet the spark plug appears dry. I've blocked the plug hole with my finger, tried to start and my finger tip is dry.  It seems that vacuum is an important component, but I don't have a vacuum flow diagram. There is a ?vacuum canister?, why? A PDF flow diagram would be real helpful along with any other ideas.
thanks
dubyajayes

[jerryscript]

There are vacuum line diagrams in the tech section. You should have one vacuum line going from the fuel petcock usually to the intake manifold. This is what allows the fuel to flow through the petcock. One way to test it all out is to put a bowl under the carb drain tube and open it up. Then take the vacuum line comming off the center of the fuel petcock and suck on it. A couple of pulls on it and you should have fuel going into the bowl, if not your fuel petcock is bad, or the fuel line is clogged somewhere.

There are a couple of canisters you may have, one for a PAIR system, and one for an EVAP system. The PAIR system would have a tube going up and down on the outside of the valve cover, and a large hose connecting to the canister, and a smaller hose connecting to either the air box or carb intake tube. The EVAP system has a charcoal canister connected to the gas tank.

One other thing to make sure of, when you put your finger over the spark plug hole and crank it, does it blow your finger out of the hole? If not, you may have a compression issue.

[dubyajayes]

Thanks for the info, I'll check the Tech section for the diagrams.  I apparently have an EVAP system according to a tag I found.  Yes, when I put my finger over the spark plug hole it does get blown out when I crank the engine.  I think I have good compression but the plug hole is smaller than the adapters I have for my cars.  I also have very weak (and sometimes no) spark at the plug so I'll chase that around.  I installed a new coil w/plug wire but get the same result as the old coil.  Could it be my CDI?  I don't understand what that is or does.
dubyajayes

[Alleyoop]

Here is a good Video on what to test and how for a NO SPARK.
About the only thing not mentioned in the Video is CHECK FOR A GOOD GROUND FROM MOTOR TO FRAME.
Alleyoop

scooterdoc.proboards.com/thread/9349/great-spark-video-tests

[Bashan]

Here's a diagram for the hoses. This is a general guideline. You may not have a PAIR or an EVAP pollution system. You may not have an ACV valve. Your tank petcock may be different and you might have a vac fuel pump rather than a vac valve. Just use your head and adapt, that's the nature of scooters.

[jct842]

ADAPT, thats what the chinese factory does when they get a pile of new parts in....they make it work.