B&S running with no exhaust, bad?


Old 05-18-06, 06:53 AM
michaeljp86's Avatar
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Join Date: May 2005
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B&S running with no exhaust, bad?

A friend has this mower with a 3.5hp briggs. It doesnt run anymore and asking if I know anything about it. I played with it a little and it would start. But it ran OK but only at low throttle, on high it would spit and sputter and this all started in the past 2 or 3 days. One thing I noticed is the muffler is rotted off, or got ripped off. All thats left is a tube that was in the inside of the muffler that screwed into the block. I was told a engine needs back pressure in the exhasut or the exhaust valve will get hot and burn up. Is this what happened? I seen it run last week and it ran fine so did no muffler finally catch up with it?
Thanks for the help
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Old 05-18-06, 04:07 PM
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,728

To check the exhaust valve you need to check the compression. If low put a small amount of oil through the plug opening, spin over the motor a few times to settle the oil and blow out any over fill, then check the compression again. If still low the valves would be suspect.

If you aren't getting any blowback through the carburetor, the intake valve is probably O.K. and the exhaust valve would be suspect.

I have heard something similar about the muffler on a four stroke; with the muffler missing, the exhaust valve would cool too quickly after shutoff. This was to lead to crystalization or warpage which would lead to burning or breaking of the valve.

I can't say I ever saw a case of it which you could definitely say it was caused by that, but it was always considered a possibility.

Hope this helps

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