I just bought a used 70cc BMX atv. I'm new to atv's but can follow instructions pretty well. I purchased a es5lbs walmart battery and installed it today (after charging). When I turned it over the starter was very slow. After about 5 turns all it did was click. Did I buy an underpowered battery? If the battery is powerful enough what should be my next step?

 

Take a meter and measure the DC voltage from the plus to minus terminals right on the battery while trying to crank the starter. What do you measure?

Do the same test, only this time measure the DC voltage from the starter motor input terminal to the case of the starter motor. What do you measure?

Jump the quad to your car battery. Crank the starter. Any change in cranking speed?

 

Checked the voltages on the battery and starter today. Both were 12.8 volts. I haven't tried jumping it off the car. For some reason that scares me. I can just see me making a mistake and melting the little quad into a puddle. Thanks so much for the quick reply. I'm going to try to jump it tomorrow.

 

Did you measure the voltages while the starter was turning? That part is important. The reason I ask is that you should have measured a slightly lower voltage at the starter due to the drop in the cables feeding the starter. Starters draw about 30-40 amps. Even big wires will have a voltage drop at those current levels.

One more question: When you measured the voltage at the starter motor (while the starter was turning), was your black meter lead on the starter motor case (and not the battery negative terminal)? This too is important in order to identify (or eliminate) any problems in the ground return path back to the battery.

If the starter voltage is indeed 12.8 volts right at the starter, while the starter is spinning slow, then is has to be a bad starter. Its getting voltage and its spinning slow. If the starter is spinning slow because the engine is too hard to turn, the starter would draw a lot more current and you would see a large voltage drop at the starter motor.

I can see why one might have reluctance to jump the little quad battery to a car. But they are both 12 volts. When you hook 12 volts to 12 volts nothing much happens. But if your little battery can't cut it, its voltage will start to drop, and the car battery props it up and provides all the necessary current. Just be sure to get the polarity right when you hook it up. As far as melting things, your wiring harness (other than the starter cables through the solenoid) is protected by a fuse.

 

I measured with the start button held in. The starter didn't want make a complete turn when I measured. It would only click. The battery was fresh off of the charger.

The black lead was on the engine block near the starter.

I'm going to try to jump it with the car today. Is that with the car running or not. When I usually jump something its with one vehicle running, but this is my first experience with quads.