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Briggs 500 158cc hard to start

Started by scmowertrouble, October 15, 2021, 06:04:50 PM

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Hi all,

I've been given a mower which is a pain to start. Once it's going it seems OK.
I don't know of its history, other than I was told it has apparently had the head gasket changed at some point before its previous owner gave it to me.

I've installed a new champion plug and a brand new genuine Briggs carb with new, fresh E5 fuel as I suspected it had old fuel or E10 in it. Neither of these have changed the symptoms. The air filter is also new and clean.

Set the throttle to the hare, prime 3 times and pulling the cord it will fire and pop/smoke. Keeping going through this with an occasional re-prime it'll slowly start to cough and splutter into life more until it eventually ticks over and dies. Keep going and it will eventually wind up to life. No smoke once it's running.

Is this previous head gasket "issue" likely to be the root cause and I'm wasting my time?


Hi, and welcome to TGMF.

I would check a couple of things.  One being the tappet clearances, especially if someone has had the head off.  Make sure they have the correct clearance because if they are too tight then you're going to have issues.

Secondly, make sure the flywheel key hasn't partially sheared which will alter the ignition timing.


Hi Mick,

Thanks for your helpful reply.

I took to YouTube to learn how to adjust the tappet clearances and bought a feeler gauge, another head gasket and a flywheel key just in case.

I went out today to start disassembling the mower and when taking off the exhaust guard found I had two 10mm sockets and was missing my 8mm. I decided to check I had the right size sockets for the head bolts and found a bolt that was less than finger tight - almost all of the head bolts were loose!
I tightened the head bolts all up, primed it and pulled the cord once, it burst straight into life!

Pulling the cord was sometimes more difficult than it should be and I thought you were onto a winner with the valve clearances but it seems a loose head will do the same. This also explains why I felt like it had low compression and the previous head gasket issue was the reason it wasn't going to end well.

Thank you for pointing me in the right direction before it ended up for spares on eBay!