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8HP Briggs Engine Backfires

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Bob

04-18-2000 15:37:53

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Last year I bought A LAwn Boy tractor from a friend. It is from about 1988 or so. Ever sice I got it It has backfired when I whut it off. If you let it idle for about 2 minutes before you shut it off that sometimes helps, but what is causing this. Adjusting the carb seems to have no effect. Other than that it runs fine once warmed up.
After reading some of the other postings it seems like I should have got a honda.

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Mike

03-25-2004 12:25:25

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

I've been a small engine mechanic for 30 years.Your problem is not as tricky as it sounds. Get an in line fuel cut-off valve to put on your tractor.These newer lawnmowes has a silenoide under the carburetor,that's what this is for.
Ya see it's still pumping fuel into combustion chamber,an every time the engiene turns,the spark plug ignites the fuel.even when slowing down.No fuel - no backfire.

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BRYAN GREEN

04-26-2000 09:46:53

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

SOUNDS LIKE FLYWHEEL KEY PARTLY BENT OR SIDE CUT,8 HP BRIGGS ARE FAMOUS FOR THIS,IT RETARDS THE TIMING AND CAN CAUSE VALVE OR PISTON BURN.

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BoB

04-26-2000 17:35:21

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Re: Re: 8HP Briggs Engine Backfires in reply to BRYAN GREEN, 04-26-2000 09:46:53

Bryan
Also After It had been run for about an hour and a half-the time it takes to cut my lawn-and I disengage the blades it will start stalling out- revveing up stalling out and doing the whole cycle to the point where it backfires and a few times and dies. No Carb adjustment will help this either. It runs fine under load thow. Is this the same timing issue?

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Tyler

10-29-2001 16:10:53

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Re: Re: Re: 8HP Briggs Engine Backfires in reply to BoB, 04-26-2000 17:35:21

Do you have a fuel filter installed? If so you should replace this because a dirty filter can cause intermittant lagging or stalling even after the engine has run for a while.
Bad or old gas can be a culprit too.

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bryan

04-27-2000 07:11:04

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Re: Re: Re: 8HP Briggs Engine Backfires in reply to BoB, 04-26-2000 17:35:21

yes bob, the reason being under load all fuel is consumed,under no load and retarded it could over fuel and try to flood causing the govenor to hunt for a smooth speed.also check for a leaking in-take manifold gasket. good luck bob.

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Bob

04-27-2000 18:00:48

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Re: Re: Re: Re: 8HP Briggs Engine Backfires in reply to bryan, 04-27-2000 07:11:04

Bryan,
Thank you very much for finally arriving on an answer to my question. Now it a matter of changing the points, right? or is there something causing the pin to become damaged? By the way the first time I ran it this year I noticed fuel had leaked from the intake manafold to block seal and was burning off. But this MAY have been because I flodded it. I'll check the bolts thow. Thanks for the help and if you have any Ideas on how to fix it from happening again.

Bob

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BRYAN

04-28-2000 06:40:17

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Re: Re: Re: Re: Re: 8HP Briggs Engine Backfires in reply to Bob, 04-27-2000 18:00:48

HI BOB NOW THAT YOU TOLD ME THIS LETS INSTALL NEW INTAKE MANIFOLD GASKETS, THERE ARE 2 OF THEM ONE MATES TO THE BLOCK THE OTHER TO THE CARB.I THINK WERE GETTING A AIR INTAKE LEAK HERE WHICH EXPLAINS WHY YOU CANT ADJUST YOUR CARB.HANG IN THERE WE`LL FIX THIS PUPPY. BRYAN PS HOW OLD IS MOTOR ?

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Bob

04-28-2000 12:15:41

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Re: Re: Re: Re: Re: Re: 8HP Briggs Engine Backfires in reply to BRYAN, 04-28-2000 06:40:17

The mower dates from either '88 or '89. I dont know the repair history as I bought it the beginning of last summer. I'm guessing not much at all was done to it. All the guy said was he changed the deck belt and the blade- aside from the oil and air filter changes and spark plug. It worked fine then (with the exception of the backfire and a very slightly loping idle.) and it progressivly got worse to the point it is at now. I'll replace the gaskets. Both of them-either Sunday or Monday and let you know. Hopefully this will bring back my carb adjustments. I'm sure you know how frustrating it is to try to adjust a carb that won't listen! I'll let you know how it goes. I check this site 2-3 times a day so If you have any other hints let me know. I'll post back about the gaskets. Thanks for the help.

bob.

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Fred

05-01-2000 10:41:43

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Re: Re: Re: Re: Re: Re: Re: 8HP Briggs Engine Backfires in reply to Bob, 04-28-2000 12:15:41

I had a 8 or 10 hp Briggs that I tried everything I knew of to tune and nothing seemed to help. Till I got the high test gas out of it and it ran fine then. (on regular gas) Nobody mentioned this so I'll throw it in for good measure----Fred

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Bob

05-02-2000 12:45:07

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Re: Re: Re: Re: Re: Re: Re: Re: 8HP Briggs Engine Backfires in reply to Fred, 05-01-2000 10:41:43

Fred,
Thanks for the suggestion but with the gas prices these days i'd be insane to put anthing over 87 octane in my mowers. It is a good point thow. I knew A guy who ran out of gas half way through mowing his lawn and siphoned gas from his 1976 MG Miget(93 octane) and tried to run it in his mower. Needless to say it didn't work- it only ran if you primed it and you would have to keep hitting the prime button to keep it running.

Bryan- I am having an unexpectedly hard time locating a pair of gaskets for the engine. Could I use some silicon gasket material that I used to repair a leaking head gasket on one of my Tecsumseh mowers? It seens to work fine and it stopped the oil leak. Would this work? If not where would I get the gaskets... Thanks Bob

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BRYAN

05-03-2000 07:37:15

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Re: Re: Re: Re: Re: Re: Re: Re: Re: 8HP Briggs Engine Backfires in reply to Bob, 05-02-2000 12:45:07

YES BOB SILICON SHOULD WORK FINE,ANY BRIGGS DEALER SHOULD HAVE GASKETS IF YOU HAVE YOUR MODLE NUMBER. GOOD LUCK BRYAN

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BRYAN GREEN

04-26-2000 09:45:37

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

SOUNDS LIKE FLYWHEEL KEY PARTLY BENT OR SIDE CUT,8 HP BRIGGS ARE FAMOUS FOR THIS,IT RETARDS THE TIMING AND CAN CAUSE VALVE OR PISTON BURN.

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clooney

04-19-2000 14:50:11

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

Bob, I have the same problem on my 16hp briggs. trimming tractor. I just let it idle for a minute or so then choke it to stop it..no bang.

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Tyler(WA)

04-19-2000 08:44:45

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

The backfire won't hurt anything. Let it POP! I had a car that would do the same after I put a glass pack on it. Lot's of fun.

"Should'a bought a Honda?" I'm told from some experts that I greatly respect that the new INTEC line of engines from B&S are every bit as good as the Honda line but with parts available and at a reasonable price. Honda is a good engine and set the standard for small engine performance but they are really proud of their parts. Many think they should be painted green if they're going to charge that much. The INTEC engines from B&S are overhead valve engines with a feature to feature match with the Honda's. They are holding up as well under service and seem to be every bit as good at a much lower cost.

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Bob

04-19-2000 20:49:22

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Re: Re: 8HP Briggs Engine Backfires in reply to Tyler(WA), 04-19-2000 08:44:45

I wasn't aware of the intec's reliability. Thank you for the insight.
Bob

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Ned

04-27-2000 20:59:33

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Re: Re: Re: 8HP Briggs Engine Backfires in reply to Bob, 04-19-2000 20:49:22

The Intec line from Briggs is intermedite level of motors. The "vanguard" is the top of the line for Briggs and comparable to the Honda.

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Bill in Mich

04-18-2000 20:46:06

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

Its unburnt fuel mixture burning off in the hot muffler. Thats why it dosent do it so much after you let it idle a couple minuets,the muffler is cooler. I have a Simplicity 16 hp that does the same thing. It is a lot of fun scaring the pants off people when they arent expecting the bang!!!, Bill

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bob

04-18-2000 21:51:16

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Re: Re: 8HP Briggs Engine Backfires in reply to Bill in Mich, 04-18-2000 20:46:06

That sounds feasable to me. If it is dark out you can see the flame coming out of the exaust. At least I know it's nothing to worry about. Thanks
Bob

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werf

04-18-2000 17:11:29

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Re: 8HP Briggs Engine Backfires in reply to Bob, 04-18-2000 15:37:53

It could have a carbon build up in the head or on the piston. The carbon stays hot and ignites the gas after you shut it off. Just a thought.

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Bob

04-18-2000 21:48:54

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Re: Re: 8HP Briggs Engine Backfires in reply to werf, 04-18-2000 17:11:29

If it was carbon is it worth taking the head off to decarbonize it? Anyway I like the idea of just leaving it and giving people a good scare, or at least keeping the neighborhood on it's toes.

Thanks bob

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