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Discussion Starter · #1 ·
Gentlemen and wisecrackers:

I've got a 1999 MTD riding mower with a 15.5 Briggs and Stratton OHV Engine.

After cutting grass for a couple of hours the battery seems mostly depleted.

It doesn't appear to be charging properly and I'm an electrical dumdum.

It never stops running while working but the next restart is very dicey.

The battery is about a year old and it still seems to be O.K.

The only volt meter I have is a load tester so it's not graduated very fine.

It shows about 12 Volts running or not and I expected 13-14 Volts running?

The thing is I can remove a battery cable with it running and it keeps running.

I'm guessing it's charging just barely enough to run but not enough to charge?

Should there be around 13-14 Volts at the battery with the Engine running??

With it running and the battery unhooked does this point to something?

I've been reading about stators, diodes, rectifiers and voltage regulators.

I assume the stator is good if the Engine runs without the battery??

Haven't found mine yet but do they all have voltage regulators??

As mentioned, I'm an electrical dumdum and looking for guidance.

Any info would be greatly appreciated !!
 

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as far as I know the things charge of the mag, maybe it is just not enought to charge the battery if the battery is a beat beat down, and by that I mean left in the machine over the winter, let die down over the winter, that kind of thing can make a new battery suck. but Im no riding expert and am just giving my two cents worth
 

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The engine runs off of its magneto, once the engine starts (via the battery), the battery is done and should only be receiving a charge. It definately sounds like the charging circuit is no longer working. There should be a rectifier box with a wire going to battery, if it’s available and cheap (should be), replace it.

you might also buy a cheap harbor freight VOM!
 

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You have magneto ignition with a separate stator coil behind the flywheel for charging. Probably the rectifier/regulator is bad. Some have a fuse in line. Check the voltage at the stator 28 volts ac minimum going in to the regulator usually 2 yellow wires. The regulator has a red wire that is the charge output to the battery that needs to be 13 or more volts.
 

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Discussion Starter · #7 ·
Appreciate the great explanation friend!!

The fuse is good and I'm guessing it's between the battery and regulator?

Check for a broken wire each way and then the regulator or rectifier?

Can the regulator be bypassed for checking purposes??

I still have a regulator bypass tool for checking 1960's cars.

Naturally the tool wouldn't work on a mower just remembering.

I don't yet even know where the rectifier or regulator is located.

This has been the most trouble free Engine that I've ever had!!

Never had to look at anything but the dipstick over the past 20+ years.

Replaced the battery a few times and the sparkplug at the same time.

Are Briggs and Stratton normally this good or am I just lucky??

I have a brand new in the package voltmeter that's a dud.

That's why I grabbed the load tester on the way to trashing the voltmeter.

I don't do much electrical so never even opened it up until this situation.


You have magneto ignition with a separate stator coil behind the flywheel for charging. Probably the rectifier/regulator is bad. Some have a fuse in line. Check the voltage at the stator 28 volts ac minimum going in to the regulator usually 2 yellow wires. The regulator has a red wire that is the charge output to the battery that needs to be 13 or more volts.
 

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When you say: "the next start is very dicey", are we talking that day...within an hour or so or are we talking you need to jump it sometimes to get it going the next time you want to cut grass? Lorne
 

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I'm going off memory here, but I think the regulator is by the oil filter and has yellow and red wires. The red should end up on the + side of the battery and the yellow wires connect to the generator coils under the flywheel and will have AC voltage while the engine is running. Key on and engine not running, the red wire at the regulator should have about the same voltage as the battery and slightly above static battery voltage while running. If the regulator is mounted to anything plastic (like my Cub), it has to be connected to a ground from the metal housing of the regulator to the engine or frame. My ground wire fell off and it stopped charging.
 

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take a chance and put on a new reg/rectifier might fix the problem and you won't have to figure out a voltmeter! the motor will run without the charging system but the pto clutch needs power to stay energized eventually it will drain the bat.
 

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I have had this issue, believe it or not, check your valve lash.
Ate a few starter motors before finding that the decompression for starting comes from valve timing at cranking speed.
It gives you the impression its electrical.

Rick
 

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I have had this issue, believe it or not, check your valve lash.
Ate a few starter motors before finding that the decompression for starting comes from valve timing at cranking speed.
It gives you the impression its electrical.

Rick
Ding, Ding, Ding! THAT is where I was heading with my question. Starts slow, but usually starts cold...once it warms up it gets worse. Lorne
 

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Discussion Starter · #14 ·
Fair question but no definitive answer yet as I've only mowed a couple of times this year.

I normally don't restart hot but the 1rd time I tried the battery was very low ind it got me thinking.

A few minutes with a 4 amp charger and it's back to life.

When you say: "the next start is very dicey", are we talking that day...within an hour or so or are we talking you need to jump it sometimes to get it going the next time you want to cut grass? Lorne
 

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Discussion Starter · #15 ·
Ding, Ding, Ding.. LOL !!!

I just remembered, before my stroke 3 yrs ago, the valve lash deal.

It slowly developed hard starting and I checked grounds, battery etc.

Jumping with a car didn't help so I was thinking it must be the starter.

It always started but just barely, grunting like an old 396 on a hot day.

Finally, I noticed there were some youtube videos with the same issue.

Guys were adjusting the valves and the hard starting problem was fixed.

Funny was none of them could explain how a valve adjustment could fix it.

Funnier, was me asking everyone I knew, how could valve adjustment matter.

No one I asked even took the question seriously until I posted on Speed Talk.

I got the usual battery, ground comments then a guy from Sweden explained it.

Finally, I took the valve cover off for the first time and they were a slight bit loose.

Tightening the lash solved that issue and I forgot about it until you guys mentioned it.

Appreciate the reminder, it might help someone else this lawn mowing season.

I'm fortunate to be even mowing and fixing it after a stroke!

This time though it's just a typical low battery issue.

Trying to figure out the charging system.

Hopefully I'm getting close.

I have had this issue, believe it or not, check your valve lash.
Ate a few starter motors before finding that the decompression for starting comes from valve timing at cranking speed.
It gives you the impression its electrical.

Rick
Ding, Ding, Ding! THAT is where I was heading with my question. Starts slow, but usually starts cold...once it warms up it gets worse. Lorne
 

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If the mower has an electrically engaged deck there is a voltage regulator on the side of the fan cover. These go bad, but also have seen the magnets come off the flywheel or the stator fail. If the deck is manually engaged they do not have a regulator - they charge at a very low rate and use a capacitor on one wire to turn the current into DC. There is a second wire to operate the lights, which actually run on AC.
 

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They’re very sensitive to valve lashing some models. But you need to isolate the issue. They should charge through the regulator/Rectifier to keep voltage well above 12V while running. But I believe they still put a slight compression relief on the intake lobe to bleed off a little compression while cranking. On the pull start engines they called it easy start. Figure out what you battery voltage is and set the lash.
 

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Discussion Starter · #18 ·
Appreciate the info, is the capacitor/diode under the flywheel or somewhere visible??

If the deck is manually engaged they do not have a regulator - they charge at a very low rate and use a capacitor on one wire to turn the current into DC. There is a second wire to operate the lights, which actually run on AC.

I already tightened up the valve lash and that fixed the hard starting issue.

The intake lobe compression release is a genius idea, whoever thought it up!,

This is a very basic mower no PTO clutch or oil filter and totally manual deck.

My only issue is the battery and or the charging system and I'm still puzzled.

It runs fine with the battery disconnected so it must be charging some??

Battery voltage is 12 Volts whether the Engine is running or not.

Trying to locate the rectifier, regulator, diode whatever it has??

They’re very sensitive to valve lashing some models. But you need to isolate the issue. They should charge through the regulator/Rectifier to keep voltage well above 12V while running. But I believe they still put a slight compression relief on the intake lobe to bleed off a little compression while cranking. On the pull start engines they called it easy start. Figure out what you battery voltage is and set the lash.
 

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The engine doesn't need the battery to run, the spark comes from the magneto. The battery's only purpose is starting the engine and lights if so equipped. When running you should see 13.5 volts at the battery. If not, it isn't charging.
 

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Most of the wiring is going to be in the back sorta under the seat. Check all that to be sure first. But as stated good possibility its the valves! Starter could be going bad too... Id bet your battery is the problem myself!
 
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