Hi there. I just discovered this forum and hope I can get help with a 4-years-old problem!!!

I bought a used 1988 Columbia lawn tractor 4 years ago, equipped with a Briggs&Stratton 14hp engine model 400707. Maybe 1 year after I got it, it stopped charging the battery while running. I replaced the battery with a new one, but it lasted for a few starts and died. If battery is fully charged, it could starts. But if I miss the start, battery will just go out of energy after a few starting attempts. Engine is starting and running fine if I boost it with my car... but if I stop the engine, it won't restart.

At magneto's connector near the engine, I measure 13.8V with engine running. As I remember from last summer, I measured 12.8V at battery (should be 13.8V, no?). Does anyone have any idea? I guess the electrical schematic would help alot...

have you checked all your connections and fuses good.

I would say that I've checked most of the connections. I've removed the bulbs in the rear lights in case of a short. Didn't check the headlight because battery was dead.

As for the fuses, I don't know where to find them. There's a module with a big wire coming from the battery (+) and another big one going to the starter. Also on this module, two smaller wires. One of them is going to one side of a little black box and the other side of this box is connected to a wire coming from the magneto. Checking each pin, they are short. So if this little black box is a fuse, then it is good. If it's a diode, then it's bad... If only anyone could find the electrical schematic :( ...

I'm new to small engines (but not to electric and electronic) and was asking to myself: what's the purpose of the magneto?

Is it supposed to work like a car alternator where the battery is there to start the car, then the alternator will recharge the battery while running so electric components used during travel won't drain battery's energy? OR the magneto is there (on my lawn tractor) only to give electricity to components that need it, like the lights, and the battery is used to start the engine without being recharged (needing an external charger when not in use)?

I really need to understand the functions of the magneto and how it works, what is used when starting my engine (note that engine turns each time so safeties are ok), and then how the battery is recharged while engine is running...

Waiting for anybody's help, explanations or schematics... Thanks!

Look what I found on Briggs&Stratton website in the FAQ section: "Typically, for an engine equipped with an alternator to properly charge the battery, it would have to be run at full throttle for more than 15 minutes at a time." That could be my problem: since I have it, I run engine at full throttle for about 3 minutes to warm up, then I always reduce engine speed, like 2 clicks lower on throttle stick, and then cut the grass. What do you think? I guess it worth a try...

If not, it could be the DC diode (found also on the site the electrical schematic for charging). The search function is useless on their site but FAQ section is full of FREE infos, manuals and schematics...