Author Topic: lawn mower will not start when hot? (Read 7869 times)

srob

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lawn mower will not start when hot?
« on: May 17, 2016, 11:12:39 AM »
Hi everyone!
I have a push lawn mower that is a couple of years old. It has a briggs and stratton engine. it starts fine the first time and will run as long as I keep it going, but then after turning it off and emptying the grass bag, it will not start until it sits for a while and cools down.

Does anyone know what is causing this?

pjm123a

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Re: lawn mower will not start when hot?
« Reply #1 on: May 17, 2016, 11:49:07 AM »
Something like this happened to me with a SCAG zero turn riding mower. It had a kawasaki engine. Would start when cold and run fine. Shut it off hot and it would crank and crank and not start until it got cold. The problem ended up being the ignition coils. There were 2 of them on the side of the flywheel. This was for a twin cylinder engine. You probably only have one for a single cylinder engine. This contains the wire that runs to your spark plug. I replaced the coils in my case. If I had to do it again I would probably try to use an emery cloth or sandpaper to clean the face of the ignition coil first before replacing it.

Hope this helps

HipGnosis

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Re: lawn mower will not start when hot?
« Reply #2 on: May 17, 2016, 11:59:15 AM »
Might be a dirty air filter.
A dirty air filter flows less air causing a rich condition (more than normal amount of fuel in the fuel/air mixture going into the engine). A cold engine needs a rich mixture to start. A hot engine needs a lean condition.
Some mower air filters are cleanable, so you just replace.
I'd also clean or replace the spark plug.

Oh, and... are you putting the mower on pavement to re-start it? The grass puts a bit of drag on the blade making it a bit harder to start.

WSUCoug1994

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Re: lawn mower will not start when hot?
« Reply #3 on: May 17, 2016, 04:39:09 PM »
I had this problem on my old mower - I believe they referred to it as vapor lock. The fuel line would get hot would turn the fuel from liquid to gas. Seem to run fine when it was cold but as it heated up the vapor lock would prevent the motor from starting until the temperature dropped.

BlueMR2

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Re: lawn mower will not start when hot?
« Reply #4 on: May 19, 2016, 05:04:33 PM »
I had this problem. Low oil level. It wouldn't start after a hot shut off. Turns out it was seizing up (couldn't even pull the cord when it was hot). Topped off the oil and it was good to go. Briggs & Stratton engines are extremely durable!

Syonyk

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Re: lawn mower will not start when hot?
« Reply #5 on: May 19, 2016, 09:59:41 PM »
Check the plug gap - coils get weaker as they get hot and may not fire a worn plug.

Most mowers have gravity fed carburetors, so vapor lock isn't a real problem.

Fuel, compression, spark. One of those is missing when hot.
My random project blog - ebikes, DIY, fans, and more: http://syonyk.blogspot.com

guitar_stitch

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Re: lawn mower will not start when hot?
« Reply #6 on: May 20, 2016, 02:53:43 PM »
1) A heat soaked coil is a possibility. They absorb heat after the engine shuts off due to the stoppage of cooling air from the flywheel. You can pull the plug and with the wire on the plug, hold the hex head against something non-painted and metal on the mower. Have someone else pull the rope (it won't take much effort with the plug out) and check for a spark.

2) You could have a loose carburetor seating. Depending on the B&S motor you have, it could be a bowl type affixed to the side of the motor, or it could be screwed to the top of a metal fuel tank. Check screw/bolt tightness.

3) Carburetor could have a dirty jet. This is not very likely.

You could shoot a short burst of ether into the carb to see if it will fire off for a few seconds. If it starts and runs for a few seconds, then you know you have a fuel/airflow problem.

How fresh is your gas? Over the course of a couple years, it starts to break down and become much less useful in a gasoline engine. It may also absorb water with the ethanol content in modern fuels.

phred

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Re: lawn mower will not start when hot?
« Reply #7 on: May 23, 2016, 01:03:46 PM »
change the spark plug and gap it to correct, change the oil and bring it up to correct level, clean the cooling fins. If this doesn't do it a mechanic will need to check the flywheel key, and the condition of the spark.
Yes, many mowers are difficult to start when over a lawn. The grass blades create too much drag.
Why are you using a grassbag? Recycle those clippings back into the soil

BudgetSlasher

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Re: lawn mower will not start when hot?
« Reply #8 on: May 24, 2016, 09:36:50 PM »
I would try everything mentioned hear already first (clean air filter, start off the grass, properly gapped spark plug, and so forth first) because I have seen several of those before, but I had one where what appear to be balls of mineral scale had formed in the gas tank and would obstruct the gas line if allowed to settle, in hind sight it explained why the mower was so had to start initially as well.

srob

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Re: lawn mower will not start when hot?
« Reply #9 on: May 25, 2016, 12:45:34 PM »
Great thanks for all of the tips guys! I am headed over there this sat to check it out and try the things you suggested--I'll let you know what I find...

srob

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Re: lawn mower will not start when hot?
« Reply #10 on: June 29, 2016, 09:34:51 AM »
just a quick follow-up...a new spark plug did the trick, even though the old one looked ok. Maybe it was not properly gapped...