Precise Engine Repair Notebook

B&S Flo-Jet Carburetor Problems

Flo-Jet carburetor

Have you had problems with the two piece Flo-Jet carburetors leaking even after putting in a rebuild kit? I have run into this problem many times and have come up with a few tricks to help resolve the problems. These fixes work most of the time and they involve some special tools a normal B & S dealer should have. Refer to the picture of the carburetor to get a better idea of what is going on. Their are three places that leaks normally occur from on this carburetor.

  • A warped bowl or upper carburetor body.
  • A bad needle seat, which is pressed in.
  • A bad seal between the nozzle and the body.

If you have a bad or warped bowl or upper body, you will need to replace it. In most cases it will be better to buy a new carburetor, rather than try to repair a major problem like warpage. I have had some success on a slightly warped bowl by putting a thin layer of Permatex Form-A-Gasket (available at auto parts stores) on each surface before installing the gasket. This stuff is resistant to gasoline.

If the carburetor has a lot of corrosion in it from water etc, you should replace the needle seat as part of the repair process. Use repair kit #394682 on gravity fed systems, in addition to the normal carburetor rebuild kit. For engines that use a fuel pump, use kit #394683. The kits contains instructions on how to remove the old seat. However, I have had problems doing it this way if the seat is corroded badly and in tight, it will not come out without damaging the carburetor. Here's a modified method I have devised to accomplish the task safely.

Using a self tapping screw from a 19069 flywheel puller, I assemble it in this way. 1/4 nut, 1/4 flat washer, 5/16 flat washer and a 3/4-12 point 3/8 drive standard socket to act as a pulling block. Screw the nut most of the way onto the bolt and with the other pieces placed in order on the bolt, screw the bolt into the old seat as in the instructions. Stop once the bolt is solid into the seat and using a 7/16 end wrench, tighten the nut down against the socket pulling the old seat out. Follow the instructions for the rest of the process. I do put a very thin layer of teflon pipe sealant on the outside of the seat to allow it to press in easily and seal better.

The other area that gives problems is the fuel nozzle seat in the carburetor body, due to corrosion. A leak here will cause fuel to seep into the intake area of the carburetor body. Here's what I do that works pretty well most of the time.

Save the old fuel nozzle, a new one comes in the rebuild kit. Remove the threads with a file or on a lathe, so that it just fits smoothly into the hole. You will need to be able to rotate it against the seat. Put a little fine valve lapping compound (part #94150) on the nozzle seat and lap it in like you would a valve by rotating the upper end of the tube between your fingers. Clean the hole out good, I use spray cleaner, then put it back together with a nice clean seat again.

I have been able to resolve most of the problems with this carburetor by using the above fixes. These fixes may not be for everyone to try, but hopefully this may help some of you dealers out there that have been pulling your hair out trying to stop the leaks in this carburetor - Bruce Perrault

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The Precise Engine Repair notebook is maintained by Bruce Perrault