Cold starting a QMB139

[kbeckwith]

Apologies not sure if this belongs here or in performance.

Is there a way to get a 49cc TaoTao to not take a full 3 minutes of cranking the starter to run on a cold start? It seems like ever Taotao I've ever owned does this.

Manual choke maybe? High performance starter? Better petcock? Bigger fuel lines? Has anyone ever found a way to solve this?

[FrankenMech]

Better tuning perhaps, my 50cc scoot always started with just a single ~3 second crank. I don't even run a choke or enrichment circuit of any sort.

[GrumpyUnk]

If this occurs after sitting for several days, you likely have low fuel in the float bowl. Two methods to get fuel into the bowl are to apply vacuum to the petcock diaphragm, which would allow fuel to flow into the bowl. A second possible action is to twist the throttle open(and closed) several times. If there is some fuel in the bowl, this would operate the accelerator pump and squirt a dash of fuel directly into the intake. That would provide a mixture that is easier to burn as a cold engine won't vaporize fuel as readily as one that is hot.
You could replace the vacuum petcock with a manual valve, which would let you supply fuel to the carb float bowl with no need to crank the engine. The vacuum petcock uses the intake vacuum pulses from cranking(and running) to open the fuel valve by pulling on one side of the diaphragm. Without vacuum, the valve is spring loaded to close.
tom

Added:  If you don't get a high idle when you start the engine, your 'byvalve' is likely not functional.  You may have a faulty part or a clogged port in the side of the float bowl that restricts fuel flow to the byvalve inlet.
tom

[FrankenMech]

Note: Some carbs do not have an accelerator pump so twisting the throttle will not help.

[GrumpyUnk]

Frank is right on the money. But, I have seen 'late model' carbs that have 'something' higher up in the carb that is diddled with by the throttle being opened. It has a cover & diaphragm in there, but I did not figure out what it does. Maybe some sort of enricher operated by vacuum or something covering or opening a 'port' when the throttle is first opened?
Old SU carbs had an adjustment you did at idle. Push up on this 'button' and if the engine rpm bumped a bit, then settled, you had the movable jet in the bottom of the venturi set properly. If it stumbled, you'd open(unscrew) the adjustment and pop it again until you got a short, quick bump in rpms.
These CV carbs are related, though distantly, to SU's of pre-emissions days. Either way, there is some sort of gizmo built into the ones I have seen that are not 'accelerator pump' equipped.
Got any ideas?
tom

[scooterpimp]

Twist throttle 2-3 times and try , if no start still another 2-3 blips of throttle works for me