Briggs & Stratton engine looses power when hot


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Old 03-09-19, 12:44 AM
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Briggs & Stratton engine looses power when hot

Hoping someone can help with some good advice....

I have a ride on mower with a B&S 400000 engine (656 cc). After about 30 mins when it seems to get hot it starts to sputter a bit then eventually loses power and cuts out.

I've changed the spark plugs, air filter, oil, fuel filter and cleaned the carburetor - which was quite clean needless to say. Engine starts fine.

I'm thinking possibly the fuel pump - else I can't figure out what else to replace.

Any ideas from those much more mechanical than I would be greatly appreciated!
 
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Old 03-09-19, 05:35 AM
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If it dies when it gets good and hot but works again after it cools I would look at the ignition coil. The next time you're mowing and it's hot and the engine dies. As soon as it dies remove the spark plug. Put the wire back on the spark plug and hold the tip of the spark plug to bare metal on the engine. Turn the key and watch the spark plug for a spark. If there is no spark then it's a good chance it's the coil.
 
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Old 03-09-19, 08:25 PM
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Try loosening the fuel cap when it starts to show signs of sputtering and see if the problem goes away.
 
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Old 03-12-19, 03:06 PM
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Thanks guys for the suggestions.

I'll try the fuel cap idea first - have read about this on other blogs - and then test to see if the ignition coil is the problem.

Weekend is coming up so I'll get back either way.
 
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Old 03-12-19, 10:51 PM
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Cheese - I tried the fuel cap suggestion and that didn't make a difference.

Guys - I noticed that when the engine starts to sputter I can see that the speed regulator on the engine block is moving - but I wasn't shifting the throttle.

I will check the ignition coil over the weekend - but any other suggestions are worth a try.

Thanks!
 
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Old 03-13-19, 05:37 AM
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That's perfectly normal. The speed regulator (governor) is a mechanical device that adjusts the throttle to help keep the engine at a constant rpm. When the engine sputters it slows down and the governor opens the throttle to try and get it back up to speed.
 
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Old 03-13-19, 11:56 AM
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Pull the fuel line to the carb when it starts to sputter and see if it is pumping fuel at a rapid pace. It sounds like it's running out of fuel. Be aware that fuel will at least dribble out and likely will shoot out, so make sure it's done safely and not towards the exhaust. Maybe put a clamp on the fuel line and put it in a bottle, then unclamp it to let it flow into a bottle.
 
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Old 03-14-19, 11:38 PM
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Sorry Cheese - don't quite follow you.

Are you saying I disconnect the fuel line to the carb while its running to check if it is pumping? Surely the engine will stop and then that will stop it pumping?

BTW - I did check the fuel line when I cleaned the carb to make sure that fuel was flowing. I've also changed the fuel filter.....but not the pump (yet).
 
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Old 03-15-19, 06:37 AM
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There is fuel in the bowl of the carburetor that will keep it running for a while.
 
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Old 03-15-19, 08:49 AM
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Just spinning it over, even if not started, will operate the fuel pump.
 
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Old 03-15-19, 02:19 PM
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OK thanks! will give this a go this weekend.
 
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Old 03-15-19, 04:43 PM
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Does it smoke at all? You could visually check the head gasket without taking it apart. Disconnect the spark plug wires and squirt a little soapy water around the perimeter of the head... then have someone crank it a little while you watch for any spray.
 
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Old 03-17-19, 10:20 PM
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Hi XSleeper
No it doesn't smoke - it's only done 120 hrs, and when I cleaned the carb it was quite clean.
 
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Old 03-18-19, 12:01 AM
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My Kohler would do the same, run for 30 min then start missing, losing power, ended up being a bad coil pack!
 
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Old 04-11-19, 07:20 PM
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Hey all
I've tested the ignition coil and fuel pump and both are working fine

I'm stuck.....thinking that I need to replace the carb as I didn't take it completely apart.

Any other ideas would be greatly appreciated.
 
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Old 04-12-19, 08:04 PM
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If it's running fine for a while until it warms up, it's not the carb. It's starving for fuel. That's either blocked or collapsing fuel lines, fuel filter, something in the tank blocking the flow, vapor lock, loss of fuel pump performance, air leak, etc...
 
 

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