Briggs & Stratton magneto

[Robotstar5]

I've got no spark on the old ride-on mower. Tried holding the HT lead a few mm from the engine while turning it over and no spark, HT coil measures 2.6K ohm. I understand how a points driven system works, but this one has a magnet in the flywheel to induce current in the coil and I can't get my head round how it's wired. One end of the HT coil is connected to the frame with a ring terminal and the frame is bolted to the engine to complete the circuit, the bit I don't understand is a second ring terminal under the same bolt goes to a wire on the ignition switch which grounds it to stop the engine, how does grounding an already grounded wire stop the engine???

I must have my stupid head on today as there can't be a much simpler ignition system

 

[angellonewolf]

i dont know the way they work but know as the fly wheel spins it passses the coil what causes a spark

 

[angellonewolf]

how old is the mower is it electrinic or do you have points on it under the fly wheel ?

have you hit any thing when last used eg hit the blades on a tree root and it poss could have sheared the key under the fly wheel

is fairly easy to cheak this loosen the big nut jam a 2/3 screw drivers under the fly wheel and give a good tap on the large nut this should loosen the fly wheel and cheak the key

those coils do give up with out no or little warning and are sealed units but there are plenty of them on ebay for around £10

 

[angellonewolf]

ops forgot cheak all the saftety cut out switches if one fails it shuts off the electics

if a sit on one there are a few

 

[Bsmith]

I've got no spark on the old ride-on mower. Tried holding the HT lead a few mm from the engine while turning it over and no spark, HT coil measures 2.6K ohm. I understand how a points driven system works, but this one has a magnet in the flywheel to induce current in the coil and I can't get my head round how it's wired. One end of the HT coil is connected to the frame with a ring terminal and the frame is bolted to the engine to complete the circuit, the bit I don't understand is a second ring terminal under the same bolt goes to a wire on the ignition switch which grounds it to stop the engine, how does grounding an already grounded wire stop the engine???

I must have my stupid head on today as there can't be a much simpler ignition system

View attachment 116981

2 of us with stupid heads on then. My grandsons little moto bike packed in, due to lack of spark. I took the flywheel off cleaned everything and put it together, still no good. It had been standing out in the rain. I spoke to a mech who said if water gets in the coil it's impossible to get it dry and working again, got a kit off ebay, coil flywheel even casing and starter recoil came with it, that lot sorted it, but,, the part of the coil that pics up the magnetism from the flywheel is bolted to the engine with no insulation. how the devil does that work? Head scratched for a while, still can't come up with the answer. Yes the cut out wires run from the frame to the ign switch then to the same bolt that holds the coil to the engine.

When replacing it is critical to have the correct space between the coil and flywheel magnets. This can be done with a piece of cardboard the right thickness held on the coil contacts and the flywheel turned so the magnets pull the coil into place, tighten the holding bolts, turn flywheel then remove the cardboard.

 

[angellonewolf]

When replacing it is critical to have the correct space between the coil and flywheel magnets. This can be done with a piece of cardboard the right thickness held on the coil contacts and the flywheel turned so the magnets pull the coil into place, tighten the holding bolts, turn flywheel then remove the cardboard.

yes corn flake packet cardboard let the magnets attach them selves tighten up the nuts and just spin the fly wheel and remove the cardboard

im sure there is a ideal gap but as its hard to get a feeler gauge to bend round and been using cardboard for years never had a problem but allways spin the fly wheel by hand to make sure it does not touch the coil or parts can come a flying

 

[the snooper]

No connection to the spade terminal should give you a spark

 

[Robotstar5]

No connection to the spade terminal should give you a spark

Tried that and still no spark

 

[gordon stephenson]

Cant remember now, but the coil wiring Was strange,Not what i would have thought,It was on a cricket pitch roller withe the engine in the ctr of the roller, Took it to a specialist in Preston, One of the wires had to go to ground which i expected would have shorted it out, But no, It worked, I m not sure if there isn't a thread on here.

 

[Robotstar5]

I'll have a look for it.

 

[BarrieJ]

yes corn flake packet cardboard let the magnets attach them selves tighten up the nuts and just spin the fly wheel and remove the cardboard

im sure there is a ideal gap but as its hard to get a feeler gauge to bend round and been using cardboard for years never had a problem but allways spin the fly wheel by hand to make sure it does not touch the coil or parts can come a flying

Generally about 12 thou I think, a business card used to suffice (other cardboards are available)!

 

[gordon stephenson]

Hi, I found it under Wipac flywheel magneto, But can't remember how to link
Wipac flywheel magneto,

http://www.mig-welding.co.uk/forum/threads/wipac-flywheel-magneto.55156/

 

[nginmu]

how old is the mower is it electrinic or do you have points on it under the fly wheel ?

I do remember being fooled once by a briggs and stratton, thinking it had no points, they were well hidden under the flywheel and then another thin aluminium-looking cover