Sunday, May 28, 2017

Briggs & Stratton 650 Series Carburetor Removal/Teardown

I have a yard sale MTD PRO 21" mower that I've been getting back into good order. The machine runs ok, but it's obviously been neglected. There's no telling what all sort of muck has accumulated in the carburetor, so I'll remove and tear down the carburetor for a thorough cleaning. Here goes.

[NOTE: 'A/F' = 'Across Flats']

1) Starter Cord freed from its convenience presentation point on the mower's handlebar, and allowed to rewind completely.

2) Upper engine shroud. (Two No. 2 Phillips recess screws.)

3) Fuel Tank:
  • Three 5/16" A/F hex head shoulder screws up top.
  • One 3/8" A/F hex head shoulder screw w/resilient washer at bottom rear of fuel tank.
  • One spring hose clamp at fuel tank output nipple.
4) Air Cleaner Cover and Air Filter Element.  (One 5/16" A/F hex head captive screw. The air filter element's part number is written on it. It's 491588S.)

That gets you to here.

5) Air Cleaner Foundation Plate w/Primer Bulb.
  • Three 5/16" A/F hex head screws.
  • Detach crankcase ventilation tube.
There's a gasket between the air cleaner foundation plate and the carburetor that's easily torn. Carefully remove the air cleaner foundation plate from the carburetor.

6) Carburetor
  •  Detach the governor link spring.
  • Two 3/8" A/F hex head screws.
  • Detach the governor link.
  • Note that there's no gasket between the carburetor and the intake pipe -- only an o-ring.
7) Carburetor Teardown

There's not much to it. Unscrew the main jet from the underside of the float bowl (1/2" A/F) and the bowl, float and needle valve can be removed. Here's what you'll have.

Not shown is the needle valve seat, which is a replaceable item.

I was pleasantly surprised to find that the carburetor was quite clean inside -- no evidence of water or sludge at all.

Note the following:
  • Float level is fixed; it's not adjustable.
  • Lubricate the main jet and its gasket with WD-40 prior to reassembly.
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