Thread: Lawnmower won't start when hot!

change the spark plug with a new one. I used to keep a spare cold plug in my pocket.

Sounds like a problem cars used to have when I was young. We called it vapour lock. Car would get hot, turn it off, wouldn't start back. Something to do with the carburettor (sp?). Wait 5 minutes and it would start right up. Mow one lawn, go have a pint and then start her up again.

Originally Posted by les88

change the spark plug with a new one. I used to keep a spare cold plug in my pocket.

My thought too. Plug that is fitted is probably the wrong one so check with the dealer.

Plugs have different heat settings.

good luck

The plug, yes, I have had that on a Honda motor.

Also try pulling the air filter out, if it starts, get a new one.
I had that on my 4 stroke mower a couple of months ago, a blocked air filter acts like you have the choke on.

Cheers guys.

At least now I have a few places to start.

1. New spark plug
2. Clean air filter
3. have pint

I am errrr 'receiving' a Briggs and Stratton repair manual on-line at the moment, so I will have a read of that and see if it refers to tuning the carburettor at all.

I have also downloaded the engine manual from the B & S website, but it was not very helpful, it contained mostly instructions on changing the oil, fuel to use, etc, not really useful when something actually goes wrong!

Cheers for the help so far, keep the suggestions coming.

Originally Posted by Spelunx

I have to idle the mower all the way down the side of the house to the front lawn.

so what's wrong with that

If changing the plug & cleaning the air filter doesn't fix it try a dose of "start Ya Bastard". If that doesn't do the job its likely to be a defective magneto coil suffering heat induced insulation breakdown.

I've got a chainsaw that does exactly the same thing so I just have smoko between logs.

11 years old... is it meant to run on leaded or un-leaded ? Wouldn't mind betting you're getting a build-up in the plug gap that shorts it out.

Originally Posted by Gumby

so what's wrong with that

Nothing, really, it's just a riteous PITA. I was concerned that it may stall or run out of petrol, and then I would have a long wait before I can restart.

Originally Posted by rod1949

11 years old... is it meant to run on leaded or un-leaded ? Wouldn't mind betting you're getting a build-up in the plug gap that shorts it out.

It is meant to run on unleaded.

How would I diagnose this? Take the plug out and look for a good clean blue spark?

Originally Posted by Spelunx

I am errrr 'receiving' a Briggs and Stratton repair manual

Briggs and Stratton dont usually get repaired, they get thrown away.

Make sure there is enough oil in the sump, some stationery engines have a dry start feature which means they wont start when the oil level is low. They will start first off because all the oil has drained back into the sump and the sensor reads that the sump has sufficient oil for it to start, when you run the motor and switch it off it takes a while for the oil to drain back into the sump so the sensor is telling the motor the oil level is too low to start. Keeping your oil level up to the "full" mark will overcome this problem. Failing that, as suggested, you may be using the wrong spark plug causing it to overheat.

Originally Posted by Spelunx

It is meant to run on unleaded.

How would I diagnose this? Take the plug out and look for a good clean blue spark?

If you're using un-leaded then it should be right.

I'd take the plug out whilst still hot to see if its got a build-up in the point gap that is actually connecting both to gether.

My reason for suggeting this is that I use to use leaded fuel in the mower and was getting this build-up in the gap. I changed to un-leaded and the problem solvered.

My simple solution to this is to whip the air filter off and tip a small amount of fuel down it's neck. Start it, and then screw the filter back on while it's idling.

Originally Posted by echnidna

If changing the plug & cleaning the air filter doesn't fix it try a dose of "start Ya Bastard". If that doesn't do the job its likely to be a defective magneto coil suffering heat induced insulation breakdown.

I've got a chainsaw that does exactly the same thing so I just have smoko between logs.

Echnidna could be right here, to check the coil pull the spark plug lead off and see if you get a spark when you pull the starter by holding the terminal close to the frame, if not let it cool down for half an hour and check for spark again if it has come back the chances are the coil is faulty. If you don't want to hold the spark plug lead attach the spark plug and sit it on the metal frame.