# Bad Diode or Stater ?



## GS4231 (May 2, 2014)

Hi all, I've got a Huskee 18.5 hp, with a Briggs & Stratton 2 cylinder, model # 42A707 engine. 
Has some kind of electrical problem that's making it hard to start. The charging indicator is reading zero. I tested voltage at the battery with the engine running and it's only 12.4 v dc. I checked the voltage coming from the twin lead near the diode; the diode side reads 12 v ac, 12.5 v dc. The ac side of the twin lead reads 10 v ac. The engine cranks over a few times with the ignition switch, but it's sluggish and won't start. But if I put a battery charger on, at 6 amps, it'll turn right over. I cleaned off the spark plugs, but still no good. 
Any ideas on what to test next to narrow down the problem ? Stater ? Valve adjustment ? Diode ?


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## Mickey (Aug 14, 2010)

By the info given, you have a charging problem. Fully charged 12V LA battery should read 12.7V. At 12V the battery is nearly discharged. Charging voltage should be a min of 13.25 and up to ~14.25V.


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## GS4231 (May 2, 2014)

I took a look at the B&S service manual. It says the first thing to check when the charging system isn't working is the engine RPM's. How are the rpm's checked on these engines ? If I get a tach to measure the sparks from 1 spark plug, is that equal to the rpm's or do I double the sparks to get the rpm's ? 2 cylinder, 4 cycle engine.


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## Mickey (Aug 14, 2010)

I wouldn't worry about RPM's, just get engine up to normal speed you use when mowing. There is nothing special about engine speed.

On these simple systems where spark is developed via the flywheel, you will have a spark for each revolution. How your tac interprets that is dependent on the make/model of the tac.


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## jhngardner367 (Apr 5, 2011)

Just curious,...but when you tested it,was the engine at full throttle (3200-3600 RPM )?
I've made service calls where the owner says it wasn't charging,and he tested it,and it was low....only to find that he was testing at just above idle!
Also,if the diode were bad,it would read ac voltage on both wires. They are both AC,but the diode converts one to DC for charging,and the AC side runs the lights.If you check the DC side,with the engine OFF,Key ON,and you have voltage on BOTH sides of the diode,the diode is bad.
Ive had one fella here ,that kept calling for service,because his tractor didn't mow with out stalling. Found out he was at too low of RPMs to keep it running with the PTO on (Said it was too loud at WOT ).
I would check the battery,too,to make sure it doesn't have a dead cell.


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## Bill Kapaun (May 8, 2007)

Are you testing the stator output with the diode disconnected?

Is this a system with 2 diodes?

Possibly if you add the *type #* of the motor, one might be able to figure out exactly which charging system you have.


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