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I got a 49cc taotao, used. When I try to start it, the armature spins, but it doesn't have enough umph to get the full start unless it is connected to a RUNNING car battery.
If the car is not running, it just backfires.
Once I've had it running and warmed up, it will start right up, but give it a half hour to cool down, and it needs another jump. All this added up makes me feel like it's not a (lone) battery issue. Thoughts?
 

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Welcome! So you're saying that a car battery at rest isn't even enough to get it started? I wonder if the starter itself is weak and thus needs more motivation to turn the engine over.
 

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Welcome! So you're saying that a car battery at rest isn't even enough to get it started? I wonder if the starter itself is weak and thus needs more motivation to turn the engine over.
Yea, unless the car is running, it just doesn't seem to be enough. Starter is brand new. Less than 2 weeks old. Was having the same issue before replacing.
 

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Oh I love Chinese scooter troubleshooting. How quickly does it start with the running car? This is quite the puzzler. My original assumption would be a bad connection somewhere or maybe it doesn't get enough fuel when cold. My last Chinese scoots (a Jinlun and a CFMoto, respectively) would start even with a weak battery.
 

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Check for corrosion on the battery terminals and also check to see if your battery is good. The battery may be just good enough to get a warm bike running but not a cold bike. Batteries are more energetic as well when they are warm.
 

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A Running car will have something like a 1.0 to 1.5 more volts on the system than a non-running car. I'd suspect a high resistance connection somewhere, terminals, ground connection, fusible link, etc.

Next suspect might be a solenoid or starter that is going bad and drawing too much power. It's voltmeter time! See what kind of voltage the solenoid and starter motor are pulling the system down to. Test one then the other. Too little voltage available and the engine control or ignition can go on strike.
 

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Discussion Starter #7
Oh I love Chinese scooter troubleshooting. How quickly does it start with the running car? This is quite the puzzler. My original assumption would be a bad connection somewhere or maybe it doesn't get enough fuel when cold. My last Chinese scoots (a Jinlun and a CFMoto, respectively) would start even with a weak battery.
It was starting right up a week ago, but I played with the throttle cable a bit and now itsa big slow to start
 

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Discussion Starter #9
It does have upgraded cdi, Coil, plug, and aftermarket carb. Not sure if any of this could have an impact
 

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But at least the parts are all $20 overnight from Amazon when they break! ...And in my experience it's frequently. Ha.

Right now I'm leaning towards what @johnnyvee is suggesting. Something is likely drawing way too much power and thus robbing the little thing of juice when it needs it most. The problem is likely present when the engine is warm too, but as the engine is already warm it doesn't need much to get it going again. I'd probably next check the starter solenoid. See if maybe any wires are corroded or loose. Heck, it could just be on its way out.

Short it out with a screwdriver. If the scoot starts you've narrowed the issue down to the solenoid or perhaps the start button.
 
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I would think a running car battery is causing more damage than good. Way too much power going to the scooter.
 
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I would think a running car battery is causing more damage than good. Way too much power going to the scooter.
I disagree. The power will be voltage times current, and the current will be voltage divided by resistance. The system doesn't know if it's being powered by a 12V motorcycle battery with 16 A*h, 12V car battery with 160 A*h, or a 12V forklift battery with 6,000 A*h and that system's resistance will be the same regardless of the voltage source. The system will draw the same power from any source of the same voltage, provided it doesn't exceed the ability of the power supply to provide power. The clue that it starts with a RUNNING car, but not a non-running car, strongly suggests that the Taotao has a high resistance somewhere in the high current circuit.

Something is pulling the voltage down to an unusable low level or something in the system has resistance that is changing with operating temperature.

One suspect is the heavy gauge lead(s) that connects the starter to the battery via the starter relay or solenoid. I've seen a cable that turned into copper oxide inside its insulation, and as part of that process it's resistance goes up. If the battery ground wire, for example, triples from .05 ohm to .15 ohm, it starts dissipating substantial power and drops the available voltage to the rest of the system. Given that chinese wire is known to often be marginally sized and of marginal quality, the wires and connections, ( like ground connection to frame, #1) would be my first suspects.

I wouldn't try to measure these with an ohmmeter, doing voltage drop measurements is much more likely to reveal issues. Here's an article on how: https://drivcat.com/docs/1519.pdf

I've suggested various meters in the past, but now I'm recommending this meter:

Kelvin is a US company based in Farmingdale NY. I've been using a Kelvin 200LE meter that I bought direct from an ad in Radio Electronics magazine over 30 years ago, and it's never failed or let me down. For $5, I think the 50LE is a lot better than the similarly priced but admittedly cheap Harbor Freight meter, and good enough to get this man's job and many other jobs done.
 

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Discussion Starter #18
Actually, it's the best advice anyone can give. Your Chinese bike will never be dependable.
I don't need dependability. I need a running scooter, or I'm stuck walking. Thanks for telling me my only method of transportation is trash, I didn't already know...
 
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