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Author Topic: Briggs and Stratton Auto Choke Problem  (Read 871 times)

Offline Mick

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Briggs and Stratton Auto Choke Problem
« on: July 07, 2019, 11:32:57 AM »
An issue I've come across on several occasions with the later Briggs and Stratton auto choke system.  This is on the later engines fitted to the new Hayter Harrier mowers, and other machines.  I just happened to have four of these over a period of two weeks.

This engine uses the thermal device found on many of the Briggs and Stratton engines nowadays.  Here's roughly how it works.

When the engine starts, and the governor cuts in, that pulls the throttle down so the engine revs at a safe and comfortable speed.  This action on the throttle shaft also nudges the choke off enough to keep the engine running comfortably.

As the engine heats up, the thermal device pushes a little plastic arm, which then leans on the choke shaft to open it fully, and continues to hold it open while the engine is hot, so it's ready for a hot restart.

What's happening is when the engine cools down, and the thermal device backs away, but the choke shaft is getting stuck, and therefore leaving the choke in the off position.  This leaves you with a engine that won't start when it's cold, or at least it will be extremely difficult to start.

The cause:  The arm on the top of the choke shaft is binding against the carburettor mounting bracket.   Now They should really press a dimple in the bracket so it clears the arm, or make the arm a few thou shorter.  I have got around this by shaving a very tiny amount of plastic off the end of the arm, or even a few passes with a bit of emery paper is enough to cure it.  Hopefully Briggs and Stratton will address this issue soon, if they haven't already.

Anyway, thought I'd share my findings.  Check out the video below, it'll help to see what I'm talking about. This was one I had on the bench recently.




Offline GardenKit

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Re: Briggs and Stratton Auto Choke Problem
« Reply #1 on: July 09, 2019, 06:41:38 AM »
Thanks for sharing that Mick and for the very clear video.

Its funny how we can get a run of these things in the workshop. This problem is one I have had a few times but not for a while now, so your post has been a good 'memory jogger' as I do tend to forget some of these things as time passes and end up reinventing the cure!

I have to admit to still being a bit of a Briggs fan and generally prefer them over the Honda GCV series, although the new Honda GCVx series seems to be a game changer and I have not yet managed to 'confuse' the auto choke into giving a hot start issue like the old models suffer from.

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #2 on: July 09, 2019, 07:16:20 AM »
Must admit they have made good progress with the auto choke stuff, but I still maintain it can't cater for every situation all engines are slightly different in their own ways.  I would personally like a manual choke control even if the throttle remains fixed, but that's just a personal preference. ;)

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #3 on: July 09, 2019, 05:36:54 PM »
Had two more machines this week with the choke stuck in the off position, One on a Harrier 41 yesterday, and one on a Toro today.   :'(

Offline GardenKit

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Re: Briggs and Stratton Auto Choke Problem
« Reply #4 on: July 10, 2019, 06:26:08 AM »
Must admit they have made good progress with the auto choke stuff, but I still maintain it can't cater for every situation all engines are slightly different in their own ways.  I would personally like a manual choke control even if the throttle remains fixed, but that's just a personal preference. ;)

I have similar thoughts Mick. "Bring back the choke cable" I often say, then I remember all those Briggs choke mechanisms on Quantum and Intek, that will not quite flip the choke arm over when the brackets get slightly bent. (don't even think about the ones on an 827 rider!) And those Honda GCV choke cables that simply will not push the choke linkage up without pushing the cable back.
I then ask myself if these auto chokes are really that bad after all.

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #5 on: July 10, 2019, 06:57:02 AM »
I agree regarding the Honda's, cable clamp just isn't good enough.  Honda though much like Stihl do appear to over complicate their throttle and choke linkages for some reason, and the simple ones work better. 

The early Briggs flippy chokes were a mare, because the arm was too short to take the spring over center enough, as you know they sorted that later on.  Then came the OHV which had a bendy control bracket which would, and still does entertain you for a good half hour trying to get it to flip the choke. lol..

Yes those problems I wouldn't miss at all.  But just to operate the choke is a simple thing, no complicated linkage as proven by some of the Chinese engines out there. So simple.

Just a shame they then go and fit a 10p cable on them, and that fails.