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Garden Tractors and Mowers Vintage lawn and garden tractors, mowers, snow blowers, snowmobiles and other old machinery that is driven by small air cooled engines.

Garden Tractors and Mowers

Briggs and Stratton Intermittent Problem


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  #1  
Old 05-09-2019, 03:54:06 PM
EddyC EddyC is offline
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Default Briggs and Stratton Intermittent Problem

We have a 20 HP B&S Intek engine (407777) in our Craftsman riding mower, from the date code seems to have been manufactured in 2002. For the last number of years we've been having an intermittent issue where it will be running along fine and then starts to run rough and usually stalls out. Sometimes it will restart right away and run fine, but usually it won't and needs to sit. After sitting it will restart and run normally. Sometimes we can get the lawn done without it happening once and other times it will happen between 1-3 times during one mow.

I've replaced the fuel pump and bypassed the fuel cutoff solenoid to no avail and do the usual maintenance at the start of every season (new plugs, air and fuel filter, etc).

My thought is to rebuild the carburetor, but before diving in wanted to see if there may be something else I could check? There were a couple of mentions about valve guides and seats with this engine, but given it starts right back up sometimes I'm not sure if that could be the cause?

Intermittent problems can be tough so any thoughts or input would be appreciated!
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  #2  
Old 05-09-2019, 04:50:02 PM
Pat Barrett Pat Barrett is offline
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Default Re: Briggs and Stratton Intermittent Problem

Those pedal, seat and lever safety switches will do exactly what you describe. Figure out if the wires to them need to be up plugged to work, or conected away from the plug. Try that first.
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Old 05-09-2019, 08:01:15 PM
EddyC EddyC is offline
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Default Re: Briggs and Stratton Intermittent Problem

Thanks for the reply. Had no idea those switches could do that as sometimes it will stumble for a while before it quits vs cutting off right away if you stand up while mowing. Maybe the wire in that circuit is occasionally chafing to ground?
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Old 05-09-2019, 08:10:17 PM
Pat Barrett Pat Barrett is offline
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Default Re: Briggs and Stratton Intermittent Problem

Those darn things all need to be done away with. It was the blade engage lever switch that would cause mine to just shut off. Leave it set for a while and it would start back up. HIGHLY aggravating
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Old 05-09-2019, 08:27:27 PM
EddyC EddyC is offline
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Default Re: Briggs and Stratton Intermittent Problem

Good to know. How intermittent was yours?

Looks like these switches all run through one wire to the same terminal on the ignition switch that then runs to the ignition module to ground it out and turn the engine off, so easy enough to disconnect the switches from the circuit as a diagnostic test.

---------- Post added at 08:27:27 PM ---------- Previous post was at 08:25:59 PM ----------

And yes, VERY aggravating!
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Old 05-09-2019, 09:02:43 PM
Pat Barrett Pat Barrett is offline
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Default Re: Briggs and Stratton Intermittent Problem

Mine would be running fine, and all of the sudden go ka put. Might mow half an hour, 45 min, and then poof die in a ditch far away from the house.
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Old 05-09-2019, 09:09:25 PM
FlJim FlJim is offline
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Default Re: Briggs and Stratton Intermittent Problem

The next time it quits and won't restart, remove the air cleaner and spray some carb cleaner in the intake. This should help steer you toward either fuel or ignition.
The symptoms are somewhat characteristic of an overheating coil. If you have never given the engine under the blower housing a good cleaning, now might be a good time because built up dirt and grass clippings can prevent an air cooled engine from cooling properly.
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Old 05-09-2019, 10:03:23 PM
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Motormowers Motormowers is offline
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Default Re: Briggs and Stratton Intermittent Problem

Check the vent in the gas cap that it isnt clogged with white gunk
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Old 05-09-2019, 10:55:22 PM
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ulgydog56 ulgydog56 is offline
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Default Re: Briggs and Stratton Intermittent Problem

if its that old, it won't hurt to rebuild the carb, you can't beleave the crap the new gas does to a carb...
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Old 05-09-2019, 11:24:41 PM
K-Tron K-Tron is online now
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Default Re: Briggs and Stratton Intermittent Problem

It sounds to me like the valve lash is not correct and as the engine operates and warms up the valve lash becomes zero, resulting in a dead engine until it cools down. This could also coincide with a bad coil. Do you have a spark tester? You should test for spark when it fails to start. It could be as simple as a plugged gas cap, but chances are it has to do with valves or ignition.

Chris
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Old 05-10-2019, 12:24:57 AM
Turbo-T Turbo-T is offline
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Default Re: Briggs and Stratton Intermittent Problem

They usually use a 90 degree fitting to attach the fuel line to the carburetor. Grass clippings can pile up there and not make the turn causing fuel starvation problems.
I got a butt chewing for spending 2hr watching the old guy mow until it happened again.
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Old 05-10-2019, 06:24:22 AM
I like oldstuff I like oldstuff is offline
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Default Re: Briggs and Stratton Intermittent Problem

Be careful with those safety interlock switches. I's a liability issue if you loan it to someone. When in the biz and someone had disabled them we wouldn't work on it. Our insurance company were nazis on that subject. Yes they're a troublesome pain in the arse but...
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Old 05-10-2019, 09:36:02 PM
Yukon Yukon is offline
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Default Re: Briggs and Stratton Intermittent Problem

Like Motormowers said . Check gas cap vent.
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Old 05-13-2019, 12:13:55 PM
EddyC EddyC is offline
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Default Re: Briggs and Stratton Intermittent Problem

Thanks for the replies. When this first started happening I did check the gas cap vent valve and it seemed OK, we also leave the cap a little loose too just in case.

Also always clean the engine at the start of the season and make sure the cooling fins are clear and can radiate, so I don't think it's overheating.

Would it restart right away sometimes if it were a valve lash issue?

For a carb rebuild, I've seen some guys reuse the old gaskets, and others just get a new aftermarket carb. The rebuild kit from B&S goes for around 75 or so and there are aftermarket kits that are significantly cheaper as are the aftermarket carbs oddly at around 45. Open to suggestions on what's the best way to go for the carb.

Seems easy enough to put in a switch that will momentarily bypass those safety switches when it starts to act up and that would be a good way to either confirm or eliminate them as the cause of the problem.
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Old 05-13-2019, 12:37:26 PM
Tracy T Tracy T is offline
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Default Re: Briggs and Stratton Intermittent Problem

its often cheaper to just replace the carb, I found this out on a stihl weed eater, the kit cost more than the carb and both prices were from the stihl dealer so not aftermarket in my case.
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Old 05-13-2019, 05:52:08 PM
FlJim FlJim is offline
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Default Re: Briggs and Stratton Intermittent Problem

Your engine has solid lifters which would lead me to rule out valve lash causing intermittent issues.
I have seen trash in the fuel tank intermittently blocking the pick up tube cause this problem.
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Old 06-13-2019, 06:13:08 PM
EddyC EddyC is offline
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Default Re: Briggs and Stratton Intermittent Problem

Well I wired in a switch that would eliminate all 3 safety switches from grounding the coils when it started to run rough, but it didn't correct the problem when it started so I don't think any of those switches is the culprit.

Figure I'll take the carb off next, disassemble and clean to see if there's anything obvious going on there. Can I reuse the old gaskets when I reassemble? I think this model has the rubber o-rings that sit in a groove in the end of the intake manifold that attaches to the heads, vs the flat paper type gasket.
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Old 06-15-2019, 12:58:49 PM
NorCalEngines NorCalEngines is offline
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Default Re: Briggs and Stratton Intermittent Problem

Check for loose or corroded ground wire. Possibly ground at safety switch junction.
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Old 06-15-2019, 01:29:11 PM
uglyblue66 uglyblue66 is offline
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Default Re: Briggs and Stratton Intermittent Problem

Hot coils can do that. CHECK and recheck valve lash.I had a issue with my similar engine and it was valva lash.
Some of the briggs twins of that era had a cam shaft issue on 1 cylinder,the lope at the top of the cam got less oil and would cause a skip.
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Old 06-15-2019, 03:13:27 PM
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Default Re: Briggs and Stratton Intermittent Problem

Quote:
Originally Posted by FlJim View Post
Your engine has solid lifters which would lead me to rule out valve lash causing intermittent issues.
I have seen trash in the fuel tank intermittently blocking the pick up tube cause this problem.
I second the restriction in the fuel supply.
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