6.75 B&S Quits running after 20 minutes, why? - Lawn Mower Forums : Lawnmower Reviews, Repair, Pricing and Discussion Forum
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post #1 of 12 (permalink) Old 07-31-2019, 11:15 AM Thread Starter
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6.75 B&S Quits running after 20 minutes, why?

Changed almost everything - coil, carburetor, gas cap, spring for automatic choke. ONLY thing I did not change was spark plug.


Here is problem - the engine starts fine and runs for about 20 minutes then shuts down and will not start again until it cools, then the process continues.


HELP!!!!!!!!!!!!!
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post #2 of 12 (permalink) Old 08-02-2019, 04:11 PM
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Has to be a fuel delivery issue. The float bowl is using more gas than it is getting. Possibilities: plugged fuel line, leaky fuel line, plugged fuel tank or gas cap not venting properly. IMHO
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post #3 of 12 (permalink) Old 08-02-2019, 06:32 PM
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Do you have an inline spark checker to see if the coil is overheating and losing spark when it dies? Even NEW coils can go bad.


Could also be a fuel problem as suggested OR a faulty gas cap vent.

Experience is something you don't get until just after you need it.
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post #4 of 12 (permalink) Old 08-07-2019, 03:05 PM Thread Starter
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fuel delivery is fine, new carburetor new fuel lines, bowl is fine, remember this happens after about 20 minutes after it has been running. I think it is related to heat. Remember I have change the following, with NEW - coil, carburetor, gas cap, spring for automatic choke. I have yet to try the spark plug.

I have yet to check with a spark tester.
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post #5 of 12 (permalink) Old 08-10-2019, 10:24 PM
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Just for the **** of it, crack the gas cap and see if the problem goes away. As far as heat is concerned - unless the fins of your machine is clogged with grass and whatnot, should not be an issue. I'm still not convinced it's not fuel related but......
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post #6 of 12 (permalink) Old 11-14-2019, 11:39 AM Thread Starter
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Update - tried everything suggested and more.
After shutting down then pulling pull cord at least 6 times, NO START.
pulled spark plug and it was dry as a bone.
WTH?
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post #7 of 12 (permalink) Old 11-20-2019, 09:49 AM
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At least now you know it's a fuel shortage. So now you can trace back through the fuel system and see if you can find the issue. Stay the course. The learning from these types of persistent issues is huge. You'll get it.

Last edited by Joe Kuhn; 11-20-2019 at 10:21 AM.
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post #8 of 12 (permalink) Old 11-20-2019, 10:28 AM
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One thing you didn't mention that I've found after a lot of tries is a smashed o-ring gasket between the carb and intake manifold (pipe). It's a simple o-ring, but if it's not right it can cause surging which isn't the same issue you're having, but it's fuel related too. Harbor Freight sells some nice o-ring kits for cheap - metric as well as regular. Good luck.
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post #9 of 12 (permalink) Old 11-20-2019, 10:42 AM Thread Starter
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Thanks - I will look at the o-ring. Got lots of those in the shop.
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post #10 of 12 (permalink) Old 11-20-2019, 04:44 PM
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Remember, you want it to die. That's when you can find this rascal. I've not had this problem so it's hard for me to help you, except to say, when it does die, troubleshooting can commence.

I've changed a lot of parts just like you've done and had it work. Parts changing is just one way. Troubleshooting is another. You're now left with troubleshooting as you've done quite a few parts changes. Wish I lived next door to you. I'd be over. I love this part of the process because the gain can be huge in terms of learning.
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