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Author Topic: Briggs and Stratton Auto Choke Problem  (Read 3428 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.

Edit:  Just want to add, that even if your engine suffers from this problem, it might not happen every time you go to start it, or when you look and check for the issue.  What I'm saying is, by the time you've trundled the machine from your shed to the lawn the vibration might have just been enough to release the choke and it'll start.  So you'll need to actually check it as shown in the video.

« Last Edit: November 30, 2019, 02:06:56 PM by Mick »



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. 

Offline PAULS LAWNS

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Re: Briggs and Stratton Auto Choke Problem
« Reply #6 on: February 01, 2020, 06:01:13 PM »
I had similar problem with two Hayter R53s that I bought a year apart. I ended up getting them converted back to primer carb ... Never had a problem after that

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #7 on: February 01, 2020, 07:13:07 PM »
Hi Paul, and welcome to TGMF.

Converting back to primer sounds a bit drastic, but glad that worked out for you.  Always going to be compromise these auto choke systems, some engines like a bit of choke to start even when warm, some don't.  Not every engine is exactly the same, which is why auto choke are so troublesome.

I do have to say though, the modern auto chokes are much closer to working now than they several years ago when they tried to do it.  ;)

Offline PAULS LAWNS

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Re: Briggs and Stratton Auto Choke Problem
« Reply #8 on: February 02, 2020, 11:48:00 AM »
Thanks for the welcome  :)

Drastic it was but after 2 dealers looking and claiming they never came across the problem (I find hard to believe) and could not offer a solution ... After a season of problems I felt I had little choice.  ... I've gone over to the Toro Super Bagger because it comes with the Honda engine. I've never had a problem with the GCV160 and will stick that or higher spec Honda when possible.
« Last Edit: February 02, 2020, 11:49:46 AM by PAULS LAWNS »

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #9 on: February 02, 2020, 01:05:26 PM »
The only real issues we've had with the Briggs & Stratton auto choke system, is when someone shuts the engine off between hot and cold, they can be a bit fussy then.

Other issues,
When warm: choke is held off by thermal device, and the engine won't start. Caused by engine running too lean. Carb needs cleaning, or float level too low, due to swollen rubber seat for float needle. (engines with metal carb).

Thermal device not working, thus choke is being applied to a hot engine, and it'll cough and splutter to a halt when trying to start. (engines with metal carb).

When Cold: Choke air vane spring missing, which is a common thing (engines with metal carb).

Then we have the latest engines with plastic carb.

Not many issues with these, other than some came over to the UK with the wrong jet module in them.  linkage is plastic and flimsy, and can jump out of position.  And had several where the choke sticks in the off position, as per fist post above. ;)

Offline NOMIS

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Re: Briggs and Stratton Auto Choke Problem
« Reply #10 on: February 02, 2020, 01:43:01 PM »
Thanks for the welcome  :)

Drastic it was but after 2 dealers looking and claiming they never came across the problem (I find hard to believe) and could not offer a solution ... After a season of problems I felt I had little choice.  ... I've gone over to the Toro Super Bagger because it comes with the Honda engine. I've never had a problem with the GCV160 and will stick that or higher spec Honda when possible.
Just as future info if needed. Its not unknown for the "Thermo Wax" auto choke device to stop working correctly on "some".. Honda engines to. Iv replaced some that ether held the choke Off when cold...and some that stayed partly ON giving partial choke when hot .

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #11 on: February 02, 2020, 02:20:36 PM »
NOMIS, thanks.  Honda have gone through a few variants of that thermo wax over the last four years, in fact they've gone through several different carb configurations as well.  Choke control plate was also replaced with a modified on on later models, that was to cure the choke staying on problem you mentioned.

They have got the choke fairly reliable now,  but the amount new machines (Mainly Honda IZY's) coming back with hunting issues is quite frankly shocking.  Let's see what 2020 and the new GCVx is like.

Offline NOMIS

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Re: Briggs and Stratton Auto Choke Problem
« Reply #12 on: February 02, 2020, 02:32:33 PM »
NOMIS, thanks.  Honda have gone through a few variants of that thermo wax over the last four years, in fact they've gone through several different carb configurations as well.  Choke control plate was also replaced with a modified on on later models, that was to cure the choke staying on problem you mentioned.

They have got the choke fairly reliable now,  but the amount new machines (Mainly Honda IZY's) coming back with hunting issues is quite frankly shocking.  Let's see what 2020 and the new GCVx is like.
Iv not had to sort the hunting issue you mention yet (other than the normal fuel starvation ) on any IZY' so far Mick. Wasn't there a different governor spring as a sub?  but im not sure if that was targeted at hunting only.

Offline PAULS LAWNS

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Re: Briggs and Stratton Auto Choke Problem
« Reply #13 on: February 02, 2020, 02:49:38 PM »
I'm running three 16" Izys (love these machines. Fast enough once sped up rpm, lightweight, reliable and cheap enough to renew one every year) and I have so far had no issues engine wise

Offline Mick

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Re: Briggs and Stratton Auto Choke Problem
« Reply #14 on: February 02, 2020, 02:58:05 PM »
I'm running three 16" Izys (love these machines. Fast enough once sped up rpm, lightweight, reliable and cheap enough to renew one every year) and I have so far had no issues engine wise

Good to hear that Paul.  Surprised you've not had an issue with at least one of them, you're obviously using good fuel and looking after it, which is a downside with modern machines, they're not so forgiving with fuel like the old engines.  They all run so lean nowadays for emissions etc.  There's also one particular carb fitted to these IZY's that plays up more than the others.  You haven't got one of those is my bet. ;)