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Grrrr! 18 hp B&S With a Mind of Its Own

422437 briggs b&s flat twin carburetor troubleshooting

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#1 Utah Smitty OFFLINE  

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Posted February 08, 2015 - 01:07 AM

I have a B&S 18 hp flat twin in my Dayton 3ZK (MTD 995). 
 

It ran great when I first bought it... I used it to till my garden spot this spring, and helped some neighbors till theirs as well.  Then, when I took it over to dethatch a neighbor's lawn, it started losing power, and it was all I could do to nurse it the 2 blocks back home... I had to keep the choke out for it to even run

 

It sat in my shed all year, until I decided to try and get it running to day.

 

I pulled the top off the carb... what you see is what it looked like when I opened it up...

 

IMG_20150207_172350_568.jpg

 

I pulled the idle and high speed mixture screws all the way out and sprayed carb cleaner into all the orifices, including the needle for the float.

 

The float was slightly low, so I pressed the tab and level it with the underside of the top casting, per the owner's manual.

 

The engine is a Briggs 18 hp flat twin with horizontal shaft. Model number is 422437 1101... built in 1981.  I can't find a points cover, so I assume it has the Magnetron system. 

IMG_20150207_194019_707.jpg

 

HOWEVER, as you can see from the first picture, it has the old style two-piece manifold, PLUS, if you'll look at the first picture at about the 2 o'clock position, you'll see that the carb has a highspeed adustment scres... something that was supposedly only made for the 16 horsepower carb (Engine model 401427, etc.)

 

Anyway, I got everything put back together, adjusted the idle and high speed needle valves, pulled the screws out of the pulse-type pump (3 screw type), cleaned and checked the gap on the plugs, then started it... it fired right up, and only stalled once.

 

I let it run at about 2000-2200 rpm for 10 minutes or so.  I then shut it down to let it cool off and put a gallon of fresh fuel in it. The existing fuel smelled fine, so I didn't chuck it.

 

After refuelling, I started it again, and let it run again for about 20 minutes.  I even drove it out of the shed.. I started and stopped it a couple times for minor things, then started it and let in run ...

 

It ran fine for about 10 minutes, when it died all of a sudden. I could only start it if I pulled the choke out.  It had plenty of fuel, etc. so I'm not sure what caused it to die.

 

Any suggestions would be appreciated... BTW, it has the brass float, so it's not like the float is sticking.

 

Thanks,

 

Smitty



#2 EricFromPa OFFLINE  

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Posted February 08, 2015 - 03:07 AM

Could either be the Fuel pump or the Coil.

 

Some times those coils will act up.I had 1 here that started and ran fine till you shut it off then it would not restart for 30 minutes or so.Ended up replaceing it and rebuilding the starter on that one.Had another one loose spark while running and shut off But it started back up fine then shut back off a few minutes later.

 

I put a cheap $25 Ebay coil in both of them and they are still running fine.

http://www.ebay.com/...=item1c4d35de4d

 

Carb kit with Fuel pump kit is really cheap.I put a kit in every briggs twin I get here.

 

$10 shipped on ebay

http://www.ebay.com/...=item3cda7c0bc9

 

The diaphragm in those fuel pumps get pretty stiff after a few years.The 1st thing I do when I get tractor here that doesn't run is clean the carb real good and rebuild the pump if it has one.If you can see a circle impression from the Spring on the diaphragm then it's getting hard and needs replaced.


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#3 superaben OFFLINE  

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Posted February 08, 2015 - 08:02 AM

Sounds like the coil is going south on you.  Usually these old 422000 series engines act about like that when the coil is dying. 

 

Does it die straight off like you smacked the key or does it coast down slowly and stutter like it is running out of fuel? 


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#4 Utah Smitty OFFLINE  

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Posted February 08, 2015 - 11:03 AM

Sounds like the coil is going south on you.  Usually these old 422000 series engines act about like that when the coil is dying. 
 
Does it die straight off like you smacked the key or does it coast down slowly and stutter like it is running out of fuel?


It starts to struggle like it's out of fuel then dies. I can usually start it again, but only with the choke pulled all the way out and it has no power.

I'll put a new pump and a new coil on it--cheap insurance at $50 or so.

Smitty
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