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wristpin
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You don't specify whether electronic ignition (not to be confused with electric /key start) or older points and condenser system. If it's the latter the trouble is far more likely to be the points or the condenser and involves removing the flywheel to have a look.
Both systems use an externally mounted ignition coil/armature assembly. If it's electronic you may find the word Magnetron on a sticker in the centre of the recoil starter cover. The other tell tail for identifying electronic is a "lump" with a trigger contact between one leg of the armature and the coil.
If electronic and no spark with the kill wire disconnected from the coil it is dud - new coil time.
Older points systems can be converted to electronic by cutting the wires that disappear under the flywheel and fitting a Magnetron trigger to a good coil or replacing a dud one with an "electronic" coil with a built in trigger.
Both systems use an externally mounted ignition coil/armature assembly. If it's electronic you may find the word Magnetron on a sticker in the centre of the recoil starter cover. The other tell tail for identifying electronic is a "lump" with a trigger contact between one leg of the armature and the coil.
If electronic and no spark with the kill wire disconnected from the coil it is dud - new coil time.
Older points systems can be converted to electronic by cutting the wires that disappear under the flywheel and fitting a Magnetron trigger to a good coil or replacing a dud one with an "electronic" coil with a built in trigger.
Wendelspanswick
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Obvious question I Know but have you tried a new plug?
DrNik
Heath Robinsons long lost son
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Ive have had the same issues, either a very poor spark or none at all, so i slacken off the coil and put a layer of masking tape across the laminated face, i then wind the engine over till the magnets (on the flywheel) line up and it sticks fast to the flywheel, then tighten up the coil, wind the engine over and peel off the tape, this gives a very very small gap, which helps when the magnets in the flywheel get weak, ive also used a piece of writing paper as a feeler gauge
wristpin
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That is more or less how BS recommend setting the air gap but masking tape is a bit thin. On the engines found on many domestic mowers the recommended gap is 6 - 10 thou and on the larger ones 10-14.
Briggs have never recommended any fancy ignition testing kit or given values for the coil primary or secondary but just said that a good coil will spark 1/4" in free air from a bare lead with a minimum of 350 rpm rotation. If you need a new coil make sure that you have the Model, Type and Code numbers that are stamped in the engine blower housing/shroud.
the snooper
getting older by the day
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make sure the kill wire hasn't rubbed through anywhere causing the problem
Pull the kill wire spade off at the coil then test for spark ,I have change an old points system on a genny to a Magnetron coil off an old lawn mower and it worked a treat.
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Pete.
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I've had three Briggs & Stratton vertical-shaft mowers and all had the same problem causing them to not run - closed up valve clearances. Two of them had no spark too but only because the plug was badly fouled from repeated attempts at starting or from misfiring. I cooked the plug end on my gas ring until it was glowing hot and that cured the sparking, though they were still very hard to start and ran poorly, because of the problem mentioned above.
Now the valve clearances are easy to do. Remove the exhaust and underneath you'll find a small plate. Remove that plate and you'll see a small chamber with two valve tops and pushrod ends. Watch them as you turn the engine over and see when they are fully closed and check the clearances with a feeler gauge. Chances are that one or both are closed up to nothing.
To fix it, take a thin flat fine-tooth file and grind a chisel point on the end. Use this point to wiggle the file between the valve top and pushrod (the valve will move against the valve spring) then once you have it in there just file a gap of about 15 thou using just the valve spring pressure to file against. It takes just a minute or two each valve.
One more thing - if you tip one of these mowers onto it's side, the exhaust ante-chamber fills up with engine oil and it'll smoke out the whole neighbourhood for 20 minutes.
KemppiFrog
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I was just given a rotorvator that had been in a shed for several years, sort of trade for a favour. B&S 5hp. from 70s. Stripped it to find that the clutch and drive system were water logged and needed serious work. But the engine was in good nick. Problem? Points. A quick clean, and it gave a good spark. The unit had little use, judging by the blades, the owner, now dead, had shelved it after it quit.. Makes me wonder..
drivewasher
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If its got points under the flywheel. There is a plastic/fibre pin that operates the points as a pushrod off the cam on the crankshaft. It's prone to sticking in it's hole if engine has been stood. Twist it out clean it with a scotch cloth, oil it n put it back.
wristpin
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Briggs valve clearances
You may have got away with that method but it's all wrong! Correct clearance is achieved by removing metal from the end of the valve stem, not the stem and follower at the same time and not 15 thou!
Briggs side valve (L head) clearances should be done with the piston 1/4inch down on the power stroke or you will upset the automatic decompression which is achieved by the cam profile. Also the correct clearances for the smaller side valve engines are 5 - 7thou for the inlet and 7-9 for the exhaust.
You may have got away with that method but it's all wrong! Correct clearance is achieved by removing metal from the end of the valve stem, not the stem and follower at the same time and not 15 thou!
Briggs side valve (L head) clearances should be done with the piston 1/4inch down on the power stroke or you will upset the automatic decompression which is achieved by the cam profile. Also the correct clearances for the smaller side valve engines are 5 - 7thou for the inlet and 7-9 for the exhaust.
Pete.
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What's to 'get away' with? This is a garden mower! Most people when they won't start just call them junk and take them to the tip so it's not like you have to worry about how long it'll last when you've just given it a new lease of life. You could spend half a day stripping the head off and flatting the valve stem then re-assembling it with new gaskets or you could spend 15 minutes removing a handful of bolts, a quick once-over with a file and be back in business before your tea is cold.
As for where to file the clearance - all that matters for such a crude engine is that there is a gap, pretty much ANY gap. How it's created is largely immaterial. The pushrod certainly won't care if it's 7 thou shorter today than it was yesterday.
wristpin
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the snooper
getting older by the day
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why should it kick back ? the timing is not being altered.
engines with cranking handles are the ones that break thumbs
pull start engines will only pull the chord out of your hand if it did kick back
wristpin
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Too big a valve gap = decompressor not working, cord snatched and thumb injured . Seen it happen, acquaintance ended up with his hand strapped up for a fortnight!
I joined this forum to benefit from the expertise and best practice of those who know far more about welding than I will ever know not how to bodge. It's a bit sad that others want to "rubbish" information given in good faith by someone who for the last 30 years has made a decent living selling and servicing small engines. - just saying!
