Rotax SR – Keeps killing battery

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    I took the kart out again and again it did not have any mid throttle response and after about 5 minutes it died and had killed the battery again. It seems like there is something killing the battery when it is running. Any ideas? I put in a new battery and it did the same thing.


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    Doug Welch

    If you are using the cheap batteries that are designed for stationary use, its entirely possible to kill them in just a few minutes. These batteries are designed for use in UPS and alarm systems and will not hold up to banging about in a race kart.

    If you are using a quality motorcycle built battery, there has to be a short in your system. I would completely remove the wiring loom from the kart and check every inch of it for a bare wire.

    Garrick Mitchell

    If you have an ammeter or 12V test light and know how to use it, check for current when the engine isn’t running. Any current indicates a short somewhere in the system. It could be a failed switch or other device, or (heaven forbid) damage within your wiring harness.

    Be patient and methodical in trying to track down a short. You can Google “tracking down short in wiring harness” and come up with descriptions like this:

    Let us know what you find!

    Doug Welch

    The wiring on the Rotax is very simple. The hot lead goes first to the starter button and then directly to the starter. That is why it will crank without the ignition switch on. From the starter button, there is a secondary lead to the ignition switch. This switch energizes the coil so that the engine will run. I have seen this switch go bad but if it is mounted in fairing like most of us, it will not short the system. If they go bad, usually the motor won’t start.

    If the battery stays charged will the ignition switch is off, the problem is not in the starter side but in the ignition side. Look very carfully for an exposed wire in this part of the loom. Peal off the sheathing if you have to as the break could be hidden. (Not likely but possible)

    When you say it kills the battery, will the battery take a charge after being completely discharged? If not, I have to ask what type of batterys are you using.

    George Durdin

    It sounds as though you may have a short in the starter brush wires, The wires will fray from vibration and then short out against the starter housing and completely drain even the best of batteries.

    Rotax service bulletin 2005-30 recommends filling in the terminal area where the wires are soldered to the positive pole with silicon to stabilize the brushes and reduce the fraying of the brushes. DO NOT use an acetate containing silicon because this could lead to rust at the terminal.

    This repair and preventive maintenance of the brushes should also work on the Parilla Leopard starter as they are the same part used by Rotax.

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