Briggs & Stratton possible coil fault?

CWatters

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I have a B&S V twin in a Toro ride on. Starts and run but occasionally after 30-60mins running it will sometimes loose power and will/would stall if I kept it loaded. Typically it recovers if left to stand for as little as 2-3 mins and might then be ok for another 30-60 mins.

First time it happened I thought the fuel tank air vent had become blocked but it's fine.

Replaced fuel filter, pump and vacuum hose as they aren't very expensive.

Today when it was misbehaving I noticed the engine wasn't running smoothly either when idling or running fast. It appears to run normal and slow alternating 2 seconds. Playing with the choke doesn't really make a difference so I'm beginning to think it's not fuel related.

Does this sound like a possible coil problem when hot?

Any idea how I might narrow down the fault before buying a pair of new coils?
 

ILENGINE

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The easiest thing to do is get one of those inline spark testers and check for spark on both cylinders. Could be a bad module that doesn't work at all or shuts down due to heat issues, or could possibly be that one of the diode in the wiring harness between the modules has went bad and is causing problems.
 

CWatters

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That's a good idea. Have ordered one from Amazon.
 

CWatters

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Spark tester arrived today.

Nice bright light both sides but it flickers on both cylinders. Hard to tell if this is coincident with the engine rpm changes.

Right hand side seems to flicker a bit more than the left.
If I run the engine with the right hand spark disconnected (so just the left firing) it runs reasonably smoothly.
If I run it with the left hand spark disconnected (so just the right firing) it's less smooth.

Will have another go with the tester when I can get the engine really hot.
 

bertsmobile1

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Diodes are heat sensitive so try removing the bridge wire between the coils to eliminate that as a cause.
The wire simply grounds out the coils to stop the engine, without the wire on the mower will only stop if the fuel solenoid is doing a good job so test it first,
then go for a mow
Please remember this is a touch on the unsafe side and is used purely for diagnosing the problem and should not be considered as a fix.
 

CWatters

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Thanks again. I will try that when our thunderstorms clear away.

Meanwhile in case anyone else finds this thread, I found the engine wiring harness showing the diodes in the cable here..

https://www.briggsandstratton.com/eu/en_gb/support/faqs/browse/engine-diagram.html
specifically
https://www.briggsandstratton.com/c...s/Files/FAQs/ignition_wiring_6_pin_ms5301.pdf

On my model (2007 Toro DH220, B&S V-Twin 441677) the part number for this bit of the harness is 698330. However that's £45 ($57) in the UK so if the diodes do turn out to be the problem I'll be getting the soldering iron out and replacing just those.
 

bertsmobile1

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you noticed they were a tad on the expensive side for 6" of wire a couple of plugs and $ 2 worth of diodes.I see a trip to Tascos in your future.
If you are not familar with soldering diodes , do it quick and clamp the wires together on the diode side with a pair of lockjaws to act as a heat sink, diodes are heat sensitive and can be damaged by slow soldering with a small iron that is too hot.
 

CWatters

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Jury still out. Cut all my grass today and mower seemed to run smoothly with the shut off disconnected but it was a fair bit cooler here today so the problem may not have occurred anyway. Think I will see how it goes for the next few cuts then reconnect for comparison.

Soldering not a problem for me, done everything from small smd to lead sheets.

Found a link suggesting B&S use 1N4007 diodes which are 1000V..

http://www.lawnmowerforum.com/showthread.php/7349-Briggs-diode-wire-harness-part-844547

Those are pretty cheap so might just replace anyway.
 

bertsmobile1

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Thats good.
the bottom end B & S engines just run a single diode on the AC output from the stator.
Nearly every mower that a customer has "fixed" either has it in circuit backwards or they used a 60W soldering iron on the cable for 20 minutes and fried the diode.
Never measured the voltage on the primary, but it would not be small so 1000V sounds reasonable.
When I took over the business I inherited a 1/2 full box of B & S plugs & terminals but for the life of me I can not get my hands on replacements so some of my latter rewires are a tad on the untidy side.
Google B & S repower guide, I think it is on the USA B & S web site and there was a direct link to it on here a while back.
That has a few typical circuit diagrams and except for a few variations like reverse cut outs and neutral cut outs , most mowers are wired up fairly well the same
Seat + brake > kill wire
and
Seat + PTO > kill wire
Two loops wired in parallel.

Just be wary as the PTO & Brake switches also get 12 V during the start sequence and cross wire the kill wire & start wires and the chip in the coils will be toasted
 

CWatters

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Thanks for that. Have seen a youtube vid where someone mentioned you can damage the coil by accidentally putting 12V on the kill terminal.

Have ordered some BY2000 diodes which have a 3A 2000V spec and possible a slightly higher temperature rating then the 1N4007. More expensive but still cheaper than the postage.
 
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