Old Briggs & Stratton sparks

I'm looking at a 1972 4hp B&S where the previous owner has diagnosed 'no spark' and got a replacement magneto coil, and the old one is still attached by a black wire.
There are now two wires going into the circuit points unit. One to the old coil and one bare ended. I'm not sure if the bare one was put on to go to the new coil but not connected.
My question is - how do these work? Does the breaker keep the coil shorted until TDC? Should I just test continuity as I rotate the engine. Do you think this extra wire was put on by the PO or is there normally two wires.? If so where does it go?

I found a really good strip down video on youtube which shows me I am missing at least the speed control vanes in the airflow.

Is one wire the alternator wire for those engines that have a battery / electric starter ??

On old Ford escorts the coil is active until the points open

The points open and as the magnetic field collapses it induces a high voltage which travels through the insulated lead into and across the spark plug gap

You probbly know this but I'm just saying

Are you sure its 4Hp not 3.5Hp ? The modern ie 80s onwards models had a electronic ignition and NO points. They were interchangeable ! one wire went to ground the other to the stop button/control. I dont think the points version has been available for decades. There were many models the numbers were stamped on the air duct over the head. If you need more info I will find my briggs manual ? Noel.

Edited By noel shelley on 18/07/2023 11:09:49

Electronic ignition is a massive improvement if you can fit it

Thanks. It is '72 as the serial number is date specific. The machine it is from was advertised as 4hp. I'll check the model no later.

I too have a manual but will need full details to get any further, also B & S spares suppliers have full diagrams of engine/ignition components.

Tony

The loose wire is likely to a kill switch that shorts the coil primary to shut off the engine.

It might say 4HP but B&S rated their engines on a ‘flash’ basis, not what the engine would provide when running continuously under power.

They continued in that way until people noticed that a 3HP engine from Honda out-performed a 5HP `B&S.

Bazyl

All genuine Briggs & Stratton ignition/carburation parts come with fitting instructions. The points system has been obsolete for years. The replacement converts the old points system to electronic ignition with minimal fuss. The spare lead is for the sop start or emergency stop start. I note the cost has risen significantly since replacing the ignition for a friend a few years ago. However, much like Myford who else would be supporting 40 - 50 year old machnes or engines.

If you require fitting instructions send me a PM with your email address and I can forward a copy to you.

Robert Butler

Edited By Robert Butler on 18/07/2023 17:54:37

It does make sense that the spare wire is for a stop switch though I have not seen this mentioned on other sources wrt the engine so well done this forum.
Testing so far did not seem to have the wire short to ground anywhere round the engine's rotation so I will have to look at taking it apart to get at the contacts.

The model number is 100232-0036-01 and they seem to be quite common. The go-to engine before Honda appeared on the scene.

If the coil is of the points type there will be a gap both sides between the coil and the laminations ! If it's electronic there will only be a gap on one side. it is switched by the action of the flywheel magnet. To set it up put 2 or 3 sheets of paper between the magnet and the laminations, this will pull the mag onto the flywheel and then do up the 2 small fixing bolts and remove the paper. That will set the air gap. IF electronic you DO NOT need the points - remove them. Do NOT loose the flywheel key ! It is aluminium do not use a steel one ! If the key has even the smallest step in it replace it. Noel.

Ah, the Dreaded Honda !, seems to have put the skids under many an engine.