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Why does my B&S Quantum 6.0 engine keep stopping?


StewartD's Avatar
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03-27-09, 01:10 AM   #1  
Why does my B&S Quantum 6.0 engine keep stopping?

Greetings from New Zealand.

I have a B&S Quantum 6.0 motor 125H02-0122-B1 02041B56. Did some research at our local library and believe from the numbers that this engine was manufactured in 2002. It's fitted to a Grillo HWT 550 line trimmer (strimmer) which I might say is a wonderful machine for taming grass.

The problem is that the engine won't keep going. It starts fine, the same way it always has, but stops after a couple of minutes running. It won't restart immediately but will do so after just a few minutes, but stops again after another couple of minutes. If you restart it sooner rather than later it seems that it also stops sooner. That's my impression anyway. I haven't actually timed it. Sometimes when you restart it quite soon it will give one backfire. Compression is fine when you pull the cord. When it first started doing this the engine cutout quite quickly, but now it sometimes cuts out more slowly, even occasionally recovering some revs but never continues running for long. I've tried pressing the prime button during this time but that doesn't help.

I have an ordinary motor mower with a Quantum 5.0 engine which uses the same spark plug so changed them over but that didn't help. I then decided to clean the carburetor. On the way to it I found that the air cleaner was pretty blocked so replaced the folded paper cleaner and cleaned the gauze cleaner. Also cleaned the carburetor but it didn't fix the problem. When I went to the small engine shop to buy the new air cleaner the man told me that the problem would be gunk in the carburetor so came home and cleaned it again but still no luck. A mechanic friend of mine also reckoned it would be the carburetor so I took the carburetor off the Quantum 5.0 and put that on it. They appear to be identical, but that didn't fix the problem either.

I've also changed from 95 to 91 octane fuel but that hasn't made any difference.

Any suggestions would be greatly appreciated. Thank you.

 
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geogrubb's Avatar
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03-27-09, 09:16 AM   #2  
It is possible the fuel cap isn't venting properly, try running it with the fuel cap loose to see if there is any improvement. Have a good one. Geo

 
Airman's Avatar
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03-27-09, 11:44 AM   #3  
Possibly the ignition module is failing. It is fairly common for ignition modules fail and later work again after cooling down.

Place an inline spark tester between the plug wire and the plug and operate the engine. When the engine shuts down attempt to restart while checking the inline spark tester for spark. If no spark the coil is bad. Wait until the engine cools and attempt to start again. If the spark returns it is an indication of an electrical breakdown when heated.


The engine does not appear to be producing spark. Should the Magnetron <i>Ignition</i> Armature be replaced?

How do I replace the <i>ignition</i>?

Inline spark testers are relatively inexpensive and available in auto parts stores for as little as $6.00 here in the U.S.

YouTube - 20610 Inline Spark Tester

Jerry's Small Engine 1299 Inline Spark Tester

 
cheese's Avatar
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03-27-09, 07:07 PM   #4  
I agree with all the above. Try loosening the gas cap, or swap the one from the other machine. If that doesn't do it, you need to check for spark when it dies.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
StewartD's Avatar
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03-30-09, 09:44 PM   #5  
Many thanks Geo for your suggestion. Tried running it with the fuel cap loose and even used fuel cap from my other mower but unfortunately this didn't fix the problem. Thanks again, StewartD.

 
StewartD's Avatar
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03-30-09, 09:48 PM   #6  
Many thanks Cheese for your suggestion. Tried running it with the fuel cap loose and swapped the fuel cap from my other mower but unfortunately this didn't fix the problem. Looks like I will have to get an in line spark tester and check out Airman's suggestion. Thanks again, StewartD.

 
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