MTFCA Forum

I'm having trouble finding the cause of fuel dripping out of a Stromberg OF carb. I've rebuilt maybe 30 of these carbs and this particular one now runs absolutely perfectly all through the load and RPM ranges and might be the best running OF I've ever had except that it drips fuel at the bottom of the throttle shaft but only after shut-down. I am using a viton tipped needle and as with most of my rebuilds I have added a fuel level sight plug. The static fuel level is just below the 1" mark and the fuel level does not raise during running or after shut-down so I know that the excess fuel is not coming from a leaking needle valve or either of the two seat gaskets. It's got me stumped. Anyone have any suggestions?

Does it continue to drip or stop after a bit? If it stops after a short time it may be you are set a bit rich and it is fuel coming back down from the intake manifold. Does it immediately stop when you turn off the fuel valve?

John : It does stop eventually after shutting off the fuel but the fuel level in the bowl does not rise (sight plug removed) above the 1" level. It's like it's drawing fuel from another circuit in the carb. I should also mention that I'm trying this particular OF on my 1926 ( with more head pressure) and all the previous OF's I've rebuilt were tested on my 1925 (tank under seat) and way less head pressure. Thanks for you input. Bruce

I had trouble with my OF carb leaking from a number of screw plugs. I used "Seal All" on the threads of each plug and the leaking problem was solved. For what it is worth. Mike

Check the shafts and their bearing holes for wear.

Thanks Mike and Greg; I've done around 30 of these carbs and this one is the nicest I've had.I don't think it was ever apart, all the tiny brass plugs had no removal marks on them, the idle jet was clean and clear with the original tiny gasket in place, and the throttle shaft and bore had zero wear (first time ever). I basically took it apart, checked the main jet gaskets, gave it the ultrasound treatment, repaired the the steel roller, and put it back together. It's without doubt the best idling and driving OF I've had, but unlike the other 29 or so it drips fuel after shut-down. The only other problem is that the choke return spring is broken but I use a different set-up anyway. I'm still puzzled about the dripping.

Mine leaked due to the upper surface of the float not being smooth. The butterfly weight regulator would get snagged at times.

Thanks Mark: I always put the float in so that the soldered tab is at the bottom so the weights act on a smooth surface. Apparently the soldered up tiny hole was put there intentionally to let the heated air escape when the sides and ends were being soldered. When that process was done, the "vent" hole was sealed.

It's a little difficult to detect a leak while the carb is on the car. I found mine, using a spare intake manifold clamped in my bench vise. I made a gas tank from an old coffee can and piped it to the carb. Then with the carb in plain view and using paper towels I found each leak one at a time. Sealed with Seal All and tried again. Might seem like a lot of work, but it worked for me. Mike

Thanks Mike but every brass plug is tight and dry as well as the two large brass hex plugs.

I'd be inclined to test on your normal (lower tank) setup. You might be surprised at the result.

In any event, some drips after shutoff from that location are not exactly unknown.

Thanks Scott; I have heard about post shut-down drips before but am still puzzled as the fuel in the bowl does not rise ( I have the sight plug removed and can actually see the fuel level staying put), so I really wonder where the excess is coming from. I'll try the OF on my '25 next week and see if the reduced head pressure has an effect. Bruce

I'm not sure how to fix a leaking shaft, other than to try to machine a new bushing to within a few ten-thousanths. Either that, or machine some grooves for o-rings.