Briggs Opposed Twin 20hp Surging

[davbell22602]

Briggs 20hp vertical shaft

461707
0143e1
9904285B

Rebuild it carb and cooked it in ultrasonic cleaner for one hour with heat. Still surges on idle and top speed. Carb just has ide speed screw. Carb doesnt have a removable seat either. This is the 4 screw fuel pump carb setup.

 

[slomo]

Wow, that's a $300 mower carb. Not even a Holley double pumper LOL.

 

[Tinkerer200]

Give it a little choke and see if that clears it up, IF so, running to lean. IF it makes it run worse, running too rich. there were about 3 different gaskets for between the carb and the air cleaner box for this engine. There is a small vent hole in the mating surface which is different with different carbs, hence the different gaskets. Check that the gasket is not blocking the vent hole. Run without air filter box as possible test.

Walt Conner

 

[davbell22602]

Give it a little choke and see if that clears it up, IF so, running to lean. IF it makes it run worse, running too rich. there were about 3 different gaskets for between the carb and the air cleaner box for this engine. There is a small vent hole in the mating surface which is different with different carbs, hence the different gaskets. Check that the gasket is not blocking the vent hole. Run without air filter box as possible test.

Walt Conner

Still surges with the air box removed. This carb has no adjustment except for the idle.

 

[SeniorCitizen]

there's your problem , the choke wasn't hooked to the air box

 

[davbell22602]

there's your problem , the choke wasn't hooked to the air box

What do you mean choke wasn't hooked to air box?

 

[Walt 2002]

You didn't say what, if any, affect adding choke had. Also, you didn't say if you visually checked if the vent hole in gasket lined up with carb vent hole.
Walt Conner

 

[davbell22602]

You didn't say what, if any, affect adding choke had. Also, you didn't say if you visually checked if the vent hole in gasket lined up with carb vent hole.
Walt Conner

Holes line up with vent hole and no change with half choke.

 

[Scrubcadet10]

Surging is usually a lean running problem, but can occasionally be caused by the governor system, hold your finger on the throttle shaft, so it stays in position, or one engine speed so to speak, if dies out, you have a fuel delivery issue.

 

[davbell22602]

Ok replaced fuel line and it runs smooth on half choke. Only adjustment is idle speed adjustment.

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