Small Engines (Lawn Mowers, etc.): no charge, stator coil, briggs and stratton

Question
QUESTION: Hello,

10+ yr old Yard machine by MTD rider mower/hydrostatic. 16.5 hp briggs and stratton ohv engine. I've had no luck figuring out the no charge issue. It was near dead, battery very slowly cranking, not enough to start engine, but barely turn it over. I jumped it, runs well, works well. Turn it off, starts right back up. Wait 10 mins, no start again. I thought it could be a stator, bought one and put it in, no difference. So, I pulled it out and put the old one back in. I got a battery since the old one was dead-ish and recharging didn't help. Now it has a new battery, I adjusted the valves and when I hook up my battery load tester, it reads in the 12-13 volts range same as before. I can jump it, mow, run as long as it has gas and after a little while shut off, it won't start again. I checked the fuse, could coil be bad? I removed the battery neg cable last night after running it, to see if it will start or not. My guess is if it won't start after 5-10 mins then it's not charging. Any ideas? Thanks.

ANSWER: With a voltmeter, test the battery voltage with the key off.  It should be about 12 volts.  Then with the engine running, test it agan, it should jump by one-two volts.  If there's no jump then it's not charging.  If there is, then you have a different problem.  

How did you adjust the valves and what's the engine model and type number?  Thanks, PK.

---------- FOLLOW-UP ----------

QUESTION: Hi,
It's model# 313777. Let's assume there is no change in volts, what then? It has new battery, newer stator(I put it back in) and valves were adjusted to .005". I adjusted coil on crank to .005" as well. Plug is cleaned and good. The fuse is good. Only thing I can think is possibly a bad coil, would a bad coil do this? I may have to search again, but I don't think there are any bad wires in there, it all looked very solid.

Answer
The magneto coil has nothing to do with battery charging.  The stator coil is what does the charging.  When adjusting the valves the piston has to be 1/4" past TDC.  You probably won't see a bad wire, you have to do continuity tests on them to find shorts.  You also have to establish if the rectifier is working and you have DC voltage from the DC circuit.  Also, you have to find what AC voltage you have coming from the stator.

This forum isn't really someplace I can give all the directions to diagnosing a charging problem.  Your best bet at this point would be to get the Briggs manual for your engine and go through all the possibilities.  Thanks, PK.