Briggs & Stratton possible coil fault?

[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.

 

[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.

 

[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?

 

[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.

 

[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.

 

[bertsmobile1]

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.

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

 

[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.

 

[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.

 

[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.

 

[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.