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Briggs Opposed Twin 20hp Surging

#1

davbell22602

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.


#2

S

slomo

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


#3

T

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


#4

davbell22602

davbell22602

Tinkerer200 said:
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
Click to expand...
Still surges with the air box removed. This carb has no adjustment except for the idle.


#5

S

SeniorCitizen

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


#6

davbell22602

davbell22602

SeniorCitizen said:
there's your problem , the choke wasn't hooked to the air box
Click to expand...
What do you mean choke wasn't hooked to air box?


#7

W

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


#8

davbell22602

davbell22602

Walt 2002 said:
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
Click to expand...
Holes line up with vent hole and no change with half choke.


#9

Scrubcadet10

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.


#10

davbell22602

davbell22602

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

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#11

davbell22602

davbell22602

I guess the only thing left to do is to replace the carb since theres no fuel/air mixture screw to adjust.


#12

S

slomo

Either your carb is dirty, missing parts inside or not adjusted proper in the linkage dept.

Boil clean the carb prior to buying a Chinese carb. Open it up and make sure you have all the parts required inside.


#13

davbell22602

davbell22602

I already cooked it for a hour in a heated ultrasonic cleaner. This is the nikki version not the walbro. Only adjustment is the idle screw. Rebuild kits dont come with a new seat. Seat isnt removeable.


#14

S

slomo

davbell22602 said:
I already cooked it for a hour in a heated ultrasonic cleaner. This is the nikki version not the walbro. Only adjustment is the idle screw. Rebuild kits dont come with a new seat. Seat isnt removeable.
Click to expand...
Those ultrasonics are not the end all of carb cleaning. You have to do it maybe 3-5 times and if then get a good clean on one.

At most those ultrasonics are for jewelry and trinkets. Most ultrasonics take the entire cooking time just to heat the water up.

Boil the carb on the stove or in a yard sale crockpot. Run at 200F for 40 mins using a dishwasher soap pod.


#15

davbell22602

davbell22602

I find that hard to believe about ultrasonic cleaners. I know experienced shops that been in business for over 30 years that use them everyday with success. Dont have a working stove or crock pot. Im just gonna replace it. Thanks for the help.


#16

S

slomo

davbell22602 said:
I find that hard to believe about ultrasonic cleaners. I know experienced shops that been in business for over 30 years that use them everyday with success. Dont have a working stove or crock pot. Im just gonna replace it. Thanks for the help.
Click to expand...
Watch videos of other people using them on carbs. They state you have to recook several times. Better tools out there that offer instant heat and are much cheaper if not free. Keep using an ultra cleaner. Doesn't seem to be working for you. Good luck with it.


#17

sgkent

sgkent

I might consider putting a tachometer on it and see what the RPM actually is at the top speed. The half choke can be making it richer, or it can be slowing the engine just enough to stabilize the governor system from oscillating.


#18

davbell22602

davbell22602

sgkent said:
I might consider putting a tachometer on it and see what the RPM actually is at the top speed. The half choke can be making it richer, or it can be slowing the engine just enough to stabilize the governor system from oscillating.
Click to expand...
top speed with half choke is 32xx. With no choke when surging is 2800 to 3100


#19

C

CraigH

Have you tried holding the governor manually to check that it's not a weak spring on it allowing it to move?
When you say surging, is the engine hunting or a slow surge up/down in revs?


#20

davbell22602

davbell22602

New carb fixed the issue. Thanks for the help.


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