With the Stromberg it may be the power valve or it's gasket are leaking, or the two bowl plugs for the main jets and their gaskets and surfaces. With the 59 it could be the power valve diaphragm leaking or it's gasket. Often times it is best to have the gasket surfaces faced to make sure they are flat.
From my experience Stromberg parts from Stromberg are the best and for the 59 use rebuilding kits from Daytona. I believe Charlie Schwindler can face the Carb. surfaces and replace the 48 throttle shaft with new shaft.
I have had those 3 bowl gaskets leak even when new.I bought a small tube of blue Hylomar and just wiped a bit on both sides of that small gasket.No more leaks.
Hey we must have passed each other many times. When I lived in Gurnee, I always got gas at the BP at 21/grand. I wish I could have found non-ethanol gas, but maybe somewhere in southern Wisconsin?
My carbs leaked with that gas. I found non-ethanol here now in TN, and my English Stromberg 97 doesn’t leak anymore.
Hey....who makes that blue Hylomar? is that a 3M product. Can you get it at chain auto parts stores.
I want to try it on my Ford EBU carburators to see if it will stop the gas leak. No, it is not the power valve. Still leaks with new power valve. The only other way they could leak is thru the jets, but I wouldn' think it would empty the bowl in a day and a half thru either one.
Crazy thing about this gas is the evaporation is so quick, you can never see a puddle or anything even if you are watching it closely.
Be careful not to double up on power valve gaskets to try to stop the leak if the gasket is leaking. You could be shooting yourself in the foot, because doing that forces the power valve bottom face to be lowered such that it may hit the power valve recess in the valve-body, which would prevent main-body from completely mating down with valve body. Then you will have vacuum leak and power valve won't be of any use.
At work we had a large grinder wheel that we used the side of it to sand the carb parts flat when we suspected them of leaking from being warped. Probably not the best thing for precision surfacing but that was all we had that was large and flat. Be careful to tighten everything evenly and not to overtighten those carb parts, all that stuff is fragile. We also had a piece of glass we could set the carb on top of, fill the bowl up and then watch the carb from underneath the throttle plate to see where the fuel was dripping from.
The final versions of carburetors had sealed float bowls when not in use. The vents were controlled by a solenoid to prevent the fuel from evaporating and contributing to air pollution. When you turned the key on the solenoid vented the fuel bowl. It worked real well, I never saw one fail. You could run a test on the bench and plug the float bowl vents for a couple of days just to see if this new fuel is evaporating that fast.