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Converting 70s Briggs & Stratton to Electronic ignition

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Mogsy Tue, 28/04/2020

Hi

I have recently been given a (late 70s?) Mountfield M4 Deluxe with a (presumably 3hp? or 3.5hp?) Briggs and Stratton engine with no spark. The engine has a side-mounted starter, which I am not really experienced with working on, I'll post some photos tomorrow of what I'm talking about.

I have taken the engine apart and the coil wiring is extremely tatty and unusable. I have had no luck trying to find a new coil for it so I am wondering if removing the points altogether and installing a newer "Magnetron" type coil would work. 
 

If so, which coil should work? 
 

Thanks

Forums

hortimech Tue, 28/04/2020

It will be a 3.5HP engine and you should be able to identify your engine from the numbers stamped into the airshroud. This will be in the format of three groups of numbers: model, type and code, the first two numbers of the code are the year the engine was made.

There used to be a kit available to upgrade a points based engine to electronic ignition, but I doubt if you would find one, so your best option will be to find a coil from a later magnetron 3.5HP engine (one built after 1982) .

 

Mogsy Tue, 28/04/2020

Here’s some photos of the machine in question

I have included photos of the side of the shroud and the old coil, which is unusable.

Also, will any 3.5hp engine made after 1982 work? Because I have found a newer (early 2000s) 3.5hp Briggs classic engine, breaking for spares that has a Magnetron coil.

Would I have to worry about timing issues?

hortimech Tue, 28/04/2020

Not sure if the coil from the later engine will fit, but if the crankshaft extension on the the later engine is the same as the original engine, it should fit.

Looking at the original coil, it could possibly be salvaged by soldering a new wire to it. If you can find a later magnetron coil, it should just bolt on and provide you set the coil to flywheel gap correctly, the timing should be correct.

wristpin Tue, 28/04/2020

The timing will be ok but just make sure that as well as setting the air gap you fit the coil the right way round. The trigger “ lump” should be at the 9 o’clock position. Most genuine coils have “ engine side “ embossed on them.

Mogsy Tue, 28/04/2020

Thanks 

How would I go about finding an older 3.5 engine with a Magnetron coil and other spare parts other than eBay, as all I can find is spares for larger (5hp+) engines. I'm also after an air filter that fits, as newer Briggs filters are a different shape.

 

Partly, the reason I'm asking is regarding the Flymo CL4 deck in the background of the first photo, which is complete, except that it is missing an engine.

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