OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S Vanguard 20hp V Twin - Backfiring on Shutdown

I have been having issues with the engine backfiring when I turn the motor off, so after some research, I thought it may have been the "Anti Afterfire Solenoid" sticking.

After pulling off the carby I discovered that it doesn't have one, but according to the B&S manual it should.

Model: 351777 - Type: 1121-E1 - Code: 05040111

I am assuming Model 351777 refers to 351700 Family and it has a Nikki carby and in Fig 60 it definitely shows it as having one.

Is it possible that the anti afterfire solenoid is an optional addition.

Hello Buckets

That's a great question.
It may be that it was recommended in hotter climes where backfiring
might occur in hotter ambient temperatures.

Hopefully, a Briggs expert will be able to shed some light (heat)

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Jack

i know when i was working at my old job , had a real honda 15hp? i think on a compressor for air , in summer it almost blew the muffler off !! but winter seemed ok , anything over maybe 28c and it sut down with a bang . ok but not at face level ! and took maybe 1 1/2 seconds , just enough time to sneak one out while closing the door , scared the #%!* out of anyone was so loud ,
changed the idle a little and richened it a tad and seemed better . then they seviced it and back to backfiring it went

Thanks for the reply CyberJack,

Yes it's a bit of a mystery to me, also now I have to find another cause for the problem, although the manual does state that a backfire will not cause damage to the motor but I'm not too sure about that in regards to the baffles in the muffler.

ps: thanks for clarifying the topic heading, I've never been any good with headings

vccomm, yes it does go off with a bang especially when you don't expect it.

I will see what comes up in any further replies before I start fiddling with the settings.

Hello Buckets and vccomm

Yes, if it happens a lot the baffles will be blasted

All we can do is wait and see if a member can offer a solution.
It may be, in the meantime, that a procedure could be to let the
machine idle for a minute or so, and then kill the engine on idle.

Is this engine fitted to an imported machine?

Cheers
------------------
Jack

1/ Yes, if it happens a lot the baffles will be blasted

Thought as much

2/ All we can do is wait and see if a member can offer a solution.
It may be, in the meantime, that a procedure could be to let the
machine idle for a minute or so, and then kill the engine on idle.

I do let it idle for a couple of minutes but when it idles, it will then idle up slightly then die down, then rinse and repeat.

3/ Is this engine fitted to an imported machine?

No, a Greenfield Evolution 2000 Mk 11 34", it originally had a smaller engine but was upgraded to this engine in 2005 by the previous owner.

Interestingly I have never had to use more than 1/2 throttle and I cut 5 acres on pretty rough terrain so it's ridiculously overpowered, but I love it.

Hi Buckets,

That's great information for the experts!
That the engine is a replacement is telling ...

It may be that the bonnet / cowling is affecting this.
I wonder whether the backfiring occurs with the bonnet removed.

Just a thought.

Cheers
------------------
Jack

I've had the mower since 2006 and the problem only started in the last couple of weeks.

Here's a link to a thread with pics of it:

https://www.outdoorking.com.au/forum/ubbthreads.php?ubb=showflat&Number=68855#Post68855

Thanks Buckets

I'm only trying to help.

The problem you have is a recent one, with a configuration
you have been using for some time - without any problem at all.

So let's see what expert members can suggest and advise.
Sorry I could be of no assistance here.

Cheers.
---------------
Jack

could it be possible that the fitter of the engine didn't fit the shut off solenoid??
if has backfired a number of times , it will have blown a head gasket, which is a very common problem on those engines.
a crook coil is the other possibility.

Hi CyberJack,

I am sorry if I have offended you in some way, it was certainly not my intention if I have especially to another Taswegian .

squizzy, thanks for the reply.

I would have thought that the new engine would have come complete and thus the solenoid would have been part of the carby?? plus it was fitted professionally so one would hope they knew what they were doing.

It only backfires once when you switch it off, and does not happen every time.

I'm pretty sure the head gasket is fine but will check out the coil.

Many Thanks

check your wiring harness to see if there is two unused plugs, most likely grey and either white or black, and if there arnt then the old motor would not have had a a fuel cut off, which would mean the fitter would have to wire it in or take it out because the engine want run if it's fitted and not wired...
just some of the issues faced in an engine transplant
get an inline spark tester, there pretty cheap, and make sure both coils are firing, you'll find a build up of oil around the bottom of the dip stick if the head gasket is blown.

Thanks squizzy, that info is very interesting, I will check it out and get back.

squizzy, there are no extra plugs, so I am leaning towards your idea that it was removed by the fitter rather than my idea of it being an optional part for the engine.

There is no build up of oil on the dipstick, so I am confident the head gasket is fine.

I might just turn the petrol tap off each time for shut down until I have more info

many thanks.

sounds like a plan....