Briggs 422707 opposed twin carb

Auto Doc's said:
Hello C.,

What does to top of the original carburetor, where the air cleaner mounts look like? The 3 larger holes on top are threaded to mount the air cleaner base. The small hole is just a fuel bowl vent. That hole should always be open and line up with the top of the carburetor vent.

From your description this sounds more like a mixture adjustment problem.

I was under the impression that the "3 screw" versus "4 screw" had to do more with the carburetor fuel pulse pump than the top of the carburetor. It's been a while since I have dealt with this style.

There is a mixture adjustment screw on the base of the carburetor directly below the pulse pump. Have you tried any adjustment to that screw?

The mixture should be adjusted with the air cleaner in place to compensate for the air cleaner element air drag. Also, the air cleaner and foam prefilter need to be kept clean.
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That carb is a no go for now!
Look at the new pics you can see the holes I'm referring to!
Im hopping to get the carb with the lower air fuel adjustment below working but have not had any luck it has been throughly cleaned and gone through several times may just be bad carb??
 
Do you understand that these aftermarket carburetors are not a direct replacement, they are made to fit multiple applications? The B&S opposed twin engine was used on all kinds of different equipment applications.

The two bowl vents drilled in the top of the carburetor cover are so a variety of air cleaner base design will still fit and allow atmospheric air in as fuel is being sent into the carburetor bowl and drawn out by the engine.

I'm not certain that drilling an extra hole in your air cleaner base will not resolve this running problem.
 
Auto Doc's said:
Do you understand that these aftermarket carburetors are not a direct replacement, they are made to fit multiple applications? The B&S opposed twin engine was used on all kinds of different equipment applications.

The two bowl vents drilled in the top of the carburetor cover are so a variety of air cleaner base design will still fit and allow atmospheric air in as fuel is being sent into the carburetor bowl and drawn out by the engine.

I'm not certain that drilling an extra hole in your air cleaner base will not resolve this running problem.
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If there are multiples of air cleaners for this engine then there must have been one that had two holes for the 4 screw carb??
Drilling another hole would be simple to fill if it did not work!
There has to be someone that has seen this application before between the two different carbs unless there is a completely different air cleaner design for the 4 screw carb!
Also there are no more Oem carbs for this engine that I can find and China carb is probably my only choice!
Have to use what I already have!
I am getting another opposed engine today will see if it has another 3 screw carb to try but unless someone chimes in with another application that I can use I will drilll the hole !
Won't be the end of the world!
Been working on this engine for a year now and have tried and used everyones input for so many things to get to this point and now it's finally down to dialing in a carb!
 
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I don't know if it is possible, but you might consider changing the main jet over from the original carburetor to the aftermarket one and see if that helps.
 
Tiger Small Engine said:
A year is a long time to work on a 25+ year old engine to get it right. Could have other issues besides carburetor because of age and hours.
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Nothing wrong with the engine!
I have many others in the rotation this one needed valve job etcetera and working on and off on it for a year!
Anyway what i have now is a simple fix all I wanted basically is some one that may have seen or did what I may still do
Drill an extra hole!
Easy to fill if it's not the answer but so far No one has answered my question?
In the meantime I have other carbs I can try or rebuild!
 
Auto Doc's said:
I don't know if it is possible, but you might consider changing the main jet over from the original carburetor to the aftermarket one and see if that helps.
Click to expand...
Auto Doc's said:
I don't know if it is possible, but you might consider changing the main jet over from the original carburetor to the aftermarket one and see if that helps.
Click to expand...
After carb works fine just not when air cleaner is on!
Would rather get original carb dialed in with the lower air fuel mixture screw !
Anyway no one has answered my original question if anyone has drilled out an extra hole in air cleaner??
Simple small hole if it works great if it doesn't fill it back in!
I will try the jet from other carb possiblely if im stuck using the 4 screw carb!
 
Hello C.,

"Nothing ventured nothing gained" is a saying that seems to fit when no one can provide a direct answer. I suspect many people have either lived with the running issue or gave up.

Aftermarket carburetors are a luck of the draw, and many have gotten better over the years, but they are still not a perfect solution as a bolt on and go option.

Drilling the extra hole will just line up with the extra bowl vent and that is no harm. It may provide some kind of "atmospheric balance" that only a well-trained carburetor engineer would be able to explain.

I've dealt with many automotive and small engine carburetors over the years, and I know they all require an ideal fuel/air "balance" to function efficiently.
 
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