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Solving the persistent leak on those old B&S flo-jet carbs


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#1 dblover OFFLINE  

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Posted July 26, 2015 - 08:36 PM

I feel your pain. The carb has this slow leak all the time. It may even run, but the leak makes it run a bit rich. You rebuilt the carb to spec and the problem continued. You got another carb and found that it also had the same problem. Most folks say it is the design of the carb and install a shut off valve to mask the problem.

The why. Where is the leak? Unless the float setting is way off or the needle stuck, the leak is from the emulsion tube. Oh, the seat on the tube must have a poor machined surface - good to check and polish .if needed. Maybe use a $0.20 tephlon washer to improve the seal. Problem fixed? Nope. The problem is the float level.

I rebuilt a couple of carbs to OEM specs and got the same slow drip. I did everything the web mentioned to resolve it. They still had the drip. I verified that the lower carb bowl did not leak with the emulsion tube installed with its jet needle - the tube's machined surface was not the leak!

Note: imagine you ran a compression test on the B&S with the tool screwed too far into the head. Then imagine the intake valve hitting the tester's fitting real hard. Like it made the screw on fitting slightly tilt and strip the spark plug hole. If this wild situation happens, the intake valve may bend and the back draft out the carb will also make the carb leak ' but only during cranking.

The answer: the factory float level is too high. Setting the float parallel to the cover when it is held upside down results in the bowl fuel level being higher the a tiny hole in the emulsion tube(jet) located in the carb throat. The fuel that dribbles out is the famous flo-jet leak.

Fix? Slightly decrease the float level to drop the fuel in bowl level just below the tiny lower hole in the emulsion tube.

IMHO: The factory float setting is too high. I resist not following OEM spec. But in this instance, the spec is bad - assuming your carb body and float are good and you properly rebuilt carb ruled out other possibilities.t.

Edited by dblover, July 27, 2015 - 07:07 PM.

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#2 boyscout862 ONLINE  

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Posted July 26, 2015 - 11:30 PM

I've got three that need this. Thanks, Rick



#3 Phluphy OFFLINE  

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Posted July 27, 2015 - 02:09 AM

I feel your pain. The carb has this slow leak all the time. It may even run, but the leak makes it run a bit rich. You rebuilt the carb to spec and the problem continued. You got another carb and found that it also had the same problem. Most folks say it is the design of the carb and install a shut off valve to mask the problem.

The why. Where is the leak? Unless the float setting is way off or the needle stuck, the leak is from the emulsion tube. Oh, the seat on the tube must have a poor machined surface - good to check and polish .if needed. Maybe use a $0.20 tephlon washer to improve the seal. Problem fixed? Nope. The problem is the float level.

I rebuilt a couple of carbs to OEM specs and got the same slow drip. I did everything the web mentioned to resolve it. They still had the drip. I verified that the lower carb bowl did not leak with the emulsion tube installed with its jet needle - the tube's machined surface was not the leak!

The answer: the factory float level is too high. Setting the float parallel to the cover when it is held upside down results in the bowl fuel level being higher the a tiny hole in the emulsion tube(jet) located in the carb throat. The fuel that dribbles out is the famous flo-jet leak.

Fix? Slightly decrease the float level to drop the fuel in bowl level just below the tiny lower hole in the emulsion tube.

IMHO: The factory float setting is too high. I resist not following OEM spec. But in this instance, the spec is bad - assuming your carb body and float are good and you properly rebuilt carb ruled out other possibilities.t.

Thinking that may be why my gas consumption is a tad high, and the recently noticed black exhaust at start up. 


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#4 glgrumpy ONLINE  

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Posted July 27, 2015 - 02:35 AM

Many, if not all of my BS have leaked. >very built them, use the manuals suggestions. Every time I start one and use, seems it needs carb adjusted after awhile. Is better in that use,but starts awful next time. Back and forth. I installed shut off valves or use ones there now when parking. I need to get into mine and try lower setting.
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#5 Sugarmaker OFFLINE  

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Posted December 20, 2015 - 09:41 AM

Just rebuilt one of these carbs on a Briggs "N". Had the slow leak, took it back apart and lowered the float. No leak! Thanks for the great tech tip!

Regards,

 Chris



#6 Eric OFFLINE  

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Posted December 21, 2015 - 08:33 PM

Good find! Manufacturer specs are not always gospel, I worked Huey's in the Navy and it is common even in the military for the guys on the ground to rewrite the manuals from time to time.It seems that the manufacturer can't always write the manuals to suit every situation and environment and that leaves the guys that use them and have the knowledge room to improve upon things. I am sure that most manufacturers have a way for you to contact them so that any change that you find works and that their engineers can replicate would be added to their manuals in an update. At least that is how it works in the military, we have a system in place for changes to be made to even our oldest manuals. Again good find and glad to know that this works! Eric.




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