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Briggs & Stratton possible coil fault?

#1

C

CWatters

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?


#2

I

ILENGINE

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.


#3

C

CWatters

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


#4

C

CWatters

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.


#5

B

bertsmobile1

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.


#6

C

CWatters

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.


#7

B

bertsmobile1

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.


#8

C

CWatters

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.


#9

B

bertsmobile1

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


#10

C

CWatters

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.


#11

B

bertsmobile1

The chips are just a Hall effect bridge,
You seem to know your way around electrics so it should make sense to you.
They used to be in a stand alone unit but now they are on a chip hard wired into the coil which now becomes a "Module" at 4 times the price.
Some also have a delay so the same crank & flywheel can be used on a lot of different mowers.


#12

C

CWatters

Thanks that's interesting. I'd never really thought much about how the spark timing was done on a B&S engine. Mines been very good to me for the past 10 years so never needed to take the top cover off until last week.


#13

C

CWatters

Humm...

I've taken the diodes out for replacement and they aren't connected as I expected.

I thought the kill wire was either open (run) or grounded (kill) and the diodes were to prevent the coils "talking" to each other. So I was expecting to find the cathodes of the diodes connected together as per the attached image. Yet it seems the anodes are connected together. I'll copy what's there but would like to understand how it's meant to work?

B&S Diodes.png


#14

C

CWatters

Ah I think I see. When running the coils must produce a negative voltage so the kill switch and diodes clamp it "up to 0V" rather then "down to 0V". If that's how it works the diode orientation makes sense.


#15

C

CWatters

Replaced the diodes with new yesterday and mower seem to run slightly better. Can't be 100% sure I've fixed it until we get some hot weather and a lot of grass.


#16

B

bertsmobile1

CWatters said:
Replaced the diodes with new yesterday and mower seem to run slightly better. Can't be 100% sure I've fixed it until we get some hot weather and a lot of grass.
Click to expand...

You mean like the chilly 20 C we had yesterday ( middle of winter down here ) :laughing: :laughing: :laughing:


#17

C

CWatters

Had to put jeans on today instead of the shorts. The heatwave we had in the UK two weeks back seems long gone. Annoying as I have lots of outside painting to do.


#18

C

CWatters

Almost a year later and I still have this problem. In the mean time I've replaced..

The diodes
The coils
The plugs
The fuel pump
The fuel filter

I've also checked to see if the valve guides have moved in the head as I read that over heating can cause them to move - but they all look the same.

Given that most of the ignition system is new I'm beginning to think it must be a fuel or governor issue?

I've noticed that the fuel filter always has a lot of air in it so I tried filling it with fuel using a syringe but after one session there was a lot of air in it again. I checked the pipe from fuel tank to filter but it looks ok and not blocked. Can't find any fuel leaks anywhere. I'm wondering if I should just replace all the fuel lines to rule them out as they aren't expensive.


#19

L

Luffydog

Does this Briggs have the double barrel carb on it. Read Thur the post haven't seen any engine numbers unless I just over looked them.


#20

B

bertsmobile1

I wish you had kept this thread running cause we could possibly have saved you a lot of money on replacing good parts.
Fuel lines are always suspect.
Down here we get just about every waste product solvent added to what is sold as "fuel" ( cause it is not petrol ) .
Thus fuel lines take a beating, and this is before ethanol damage.
So yes replace the fuel lines , use good ones from a mower shop, not cheap off ebay, a lot of it is stuff that failed the mower companies QC and was rejected.
Also get some sort of spare tank, one off an old push mower will be fine.
When the mower plays up, quickly hook up the alternative tank , even if you have to hold it up in the air with your hand.
If the problem goes away then you have loose or floating debris in the fuel tank that gets sucked into the outlet and partially plugs it so the mower is just not getting quite enough fuel.
If there are any leaks in the fuel lines then the pump will pull air into the lines ( bubbles in the filter )
When you take the old filter off, cut it in 1/2 lengthways so you can see the position of the outlet.
I often fit them backwards to prevent air locks.
They work exactly the same either way except the right way around the debris will be visible on the outside of the element and backwards the debris will be hidden inside the element.
Filters are cheap so they should get replaced every season or so thus it does not really matter and the flow from them is easily tested.


#21

Boobala

Boobala

WHY are you posting the SAME issue several times ........ it makes for confusion !!


#22

C

CWatters

Luffydog said:
Does this Briggs have the double barrel carb on it. Read Thur the post haven't seen any engine numbers unless I just over looked them.
Click to expand...

The engine is a 441677 type 0136 E1. Not sure if it's a double barrel carb, don't think so. The B&S parts list for this engine say it's an 699807 which Google finds all over the web but no obvious mention of it being a double.


#23

C

CWatters

bertsmobile1 said:
I wish you had kept this thread running cause we could possibly have saved you a lot of money on replacing good parts.
Fuel lines are always suspect.
Down here we get just about every waste product solvent added to what is sold as "fuel" ( cause it is not petrol ) .
Thus fuel lines take a beating, and this is before ethanol damage.
So yes replace the fuel lines , use good ones from a mower shop, not cheap off ebay, a lot of it is stuff that failed the mower companies QC and was rejected.
Also get some sort of spare tank, one off an old push mower will be fine.
When the mower plays up, quickly hook up the alternative tank , even if you have to hold it up in the air with your hand.
If the problem goes away then you have loose or floating debris in the fuel tank that gets sucked into the outlet and partially plugs it so the mower is just not getting quite enough fuel.
If there are any leaks in the fuel lines then the pump will pull air into the lines ( bubbles in the filter )
When you take the old filter off, cut it in 1/2 lengthways so you can see the position of the outlet.
I often fit them backwards to prevent air locks.
They work exactly the same either way except the right way around the debris will be visible on the outside of the element and backwards the debris will be hidden inside the element.
Filters are cheap so they should get replaced every season or so thus it does not really matter and the flow from them is easily tested.
Click to expand...

The filters I've been using have an arrow on them to indicate the intended flow direction. Installed that way the dirt would be visible through the outer casing of the filter which is transparent. I've never seen anything in the filter but have replaced them regularly. Had to replace it again a month back when I broke it in my frustration trying to get the fuel line off quickly.

If I pull it off before the filter fuel flows out under gravity rapidly so pretty sure nothing in the tank causing a blockage.

Generally the fuel here in the UK seems pretty good. I use the same fuel in my car and fill cans at the same time.

Think if there is a fuel system issue it's probably nearer the engine but I have new pipe on order and will work through the system starting at the tank again just to be sure.


#24

C

CWatters

Possibly solved...

Ok so yesterday I drained the tank and replaced all the fuel lines from tank to carb. Some of the lines looked like they might have tiny cracks/splits near where they connected to things like the tank or fuel switch. I don't think any went right through and no fuel leaks detected.

I let the tank dry out with the filler cap off and had a look inside before vacuuming out the inside. There was some debris in there but I couldn't say anything was a definite candidate to block the outlet.

However I was surprised how small the fuel outlet was. I didn't measure it but it was slightly under 3mm (<1/8") so I can see how a blockage might occur. There is also no "upstand" so if you do run out of gas anything in there could go down the fuel pipe.

Anyway I filtered the gas and put that back in. Today I spent nearly two hours cutting grass and it didn't cut out on me! It did hiccup but that was when I was going over some rather bumpy ground.

It's a bit early to say it's solved/fixed because the grass was quite short but I will post back here to confirm.


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