Briggs and Stratton 12 hp engine

[vhgmcbuddy]

Hi,Just got this engine in a snapper mower which is old but hardly used condition. afraid to say no spark so cleaned the outer fly wheel and also the coil{removed stop wire also} still no go so removed fly wheel and cleaned the coil field and blew out the dirt from the inner part of the fly wheel still no go fly wheel key is good so no timing issues Any ideas gents Regards ROB

[stuart]

Presuming the engine is equipped with the “Magnetron” ignition coil simply remove the thin,black ignition ground wire (stop wire) from the coil and try again.If it now sparks then you have a safety switch problem.If it still don’t spark then a new coil is required.

[wristpin]

The coil under the flywheel will be the battery charging coil for an electric start machine and does not affect the ignition but if its a points ignition engine there will be a circular “tin” cover within the inner circumference of that coil with the crankshaft protruding in its centre. Within that cover will be contact breaker points and a condenser. the points may need to be cleaned.
If no points, you have an engine with Magnetron electronic ignition which is all contained within the external ignition coil. With the kill wire removed from the coil (eliminates the effect of any safety switches) and the engine rotated at more than 350 rpm you should get a spark off the end of the plug lead that will jump 1/4″. No spark probably indicates a failed coil.
Be aware that on an electric start machine a faulty ignition switch can send battery voltage down the kill wire and into the coil, killing it for good!

[vhgmcbuddy]

Thank you all it a magnestron and ive also found a safety switch at the blade drive so its work in progress when the rain stops. Can you get the ignition coil off the engine tested at a briggs and stratton agent Regards Rob

[stuart]

No point it getting it tested as they will (or should) only tell you what we have already stated (if it don’t spark with the stop wire removed the coil is dead).

[wristpin]

Before you lay out for a new coil there is one thing worth trying. Remove the coil and make sure that the face of the two supporting pillars is clean and free from corrosion and the same for the area on the coil armature (laminations) that sits on the pillars. then reinstall the coil with the necessary 10-14 thou air gap between it and the flywheel.
Best way to set the air gap is to turn the flywheel so that the magnet is at six o’clock, refit the coil pulled as far from the flywheel as it will go and tighten one retaining screw, leave the other just loose. Rotate the flywheel so that the magnet is under the coil, insert your non magnetic air gap gauge (double thickness of old micro fiche or brown luggage label!) between the coil and flywheel and slacken the screw. The magnet will pull the coil down onto the gauge. Tighten both screws and rotate the flywheel to extract the gauge.
Note that the coil must be installed so that the flywheel magnet rotating in a clockwise direction passes the “lump” of the magnetron module first. Genuine Briggs coils are marked inside or outside (can’t remember which!!)
Then do the spark test again and if no spark feel safe to spend forty quid!

[Author]

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