62 Morris Minor pickup, spun aluminum fuel tank mounted in the bed. Original installer had a shut off valve at the tank outlet but it liked to leak so the next owner removed it (this MM was once owned by a friend of Elvis). The fuel will now siphon through the electric fuel pump and goes through the needle and seat on the Weber carb and slowly fills the crankcase. Would like to stay away from an electric or mechanical shut off valve (wife driven). Maybe plumb the fuel line above the tank at some point? There might be room under the hood for that. Looking for innovative HAMBr prevention suggestions. TY for your thoughts.
They make, for Norton motorcycles, anti-wet sump valves for the oil system. Might work for gas. The electric pump would push it open I'm sure as the oil pump normally sucks it open. https://www.jrcengineering.com/technical-support/anti-wet-sump-check-valve-install/ Or maybe someone makes one for gas? I don't think raising the line will help.
Is the breather from the crankcase connected direct to the intake manifold? If so disconnect this and install a breather bottle . Normally fuel in the manifold needs to get into the combustion chamber and past the rings. You can also use a fuel shut-off solenoid from a propane duel fuel conversion and connect it to the ignition switch. These are very reliable and also have a manual override knob.
as suggested, the best solution is to fix the carb. if for some reason that is not possible, get a motorcycle shut off valve. they use engine vacuum to open…. engine not running/ no fuel flow. just not sure you will find one that flows enough for your needs.
In the marine world a anti siphon valve is required at the tank. Normally pipe thread on one side and 3/8 hose barb on other. It has a spring and ball inside. Basically a check valve. The gas can’t siphon out but the pump has enough power to open it when it’s running. And I also would get the needle and seat fixed.
I’m having a hard time understanding how any siphoning to the carburetor could overcome the float seat, but not be noticed when the engine is running and the fuel is pressurized to the inlet and not? causing an issue. Is this a Weber issue (I know nothing about them)?
I assume that the fuel outlet is on the bottom of your tank? If so I see two options: convert tank to draw off the top of the tank, or as mentioned, a check valve or shutoff of some type at the tank. And as others have mentioned, check over the carb for good measure. Even though it's more work converting the tank to top draw, it's the overall safest. Does the tank have a roll over shutoff in the tank vent?
I know the OP mentioned no electrics, I get that. One of our fire trucks though kept filling the crankcase of the Briggs pump engine, I guess the tank mounted much higher up made enough pressure to push the needle down, don't know. But I installed an electric solenoid powered off the ignition switch, no extra switch, and it worked great. Since he has an electric pump already he could just jumper over from there.
It makes no difference with fluid mechanics. The "head" is still the same [the height difference between the fluid levels in the tank and the float bowls] The weight of the fluid drawing upwards from the top of the tank is counteracted by the extra weight of the fluid flowing downwards . The only advantage is no holes / fittings in the bottom of the tank Weber carbs only need 3-4 psi , and if it is a DCOE it needs to be mounted at the corrected angle. Road racers can suffer splutter on L/H corners but not R/H corners etc [depending on which side the carbs are mounted on] You can buy a "Viton" tipped needle and seats for Weber carbs, these require more pressure to overcome seat pressure. Weber carbs are also susceptible to floats leaking and filling up with gas
I'm trying to understand how the leaking carb is filling the crankcase without filling up the cylinders and hydro-locking the engine. With cam driven fuel pumps the gasoline can enter the crankcase, This is normally a ruptured diaphragm on the mechanical pump.
Well with the fire engine, the pump would sit unrun for weeks at a time, time enough for the gas to seep past the rings I guess.
You can put enough fuel in a crankcase to be damaging trying to start a flooded engine , fuel has no problem getting by the rings , like blow-by sez , fuel will get past rings just from sitting .
I was referring to the OP's engine . But on a B&S engine they are usually side valve. Leaking gas would seep past the intake valve guide
I installed a electric fuel shutoff solenoid valve on my RPU that also has a manual bypass to turn it on if for some reason the solenoid fails to open the valve when it’s energized. Works perfectly and fuel won’t siphon from the tank when shut down. Details here https://www.jalopyjournal.com/forum...-up-build-thread.460009/page-90#post-13838594
Many motorcycles etc. use a vacuum operated valve at the tank. Connected to intake vacuum, opens when engine starts, closes when engine turns off. Can have a manual override to open, for example for starting after draining the carbs.
TY for the suggestions. The downdraft Weber is less than a year old so the needle and seat should be ok. Have a gravity fed Model T also that likes to leaks through the 100 year old needle and seat but with the updraft carb mounted low, the fuel doesn't enter the crankcase. This tank couldn't be lowered enough, thought about going back to an original tank. The best solution is probably as suggested, some type of fuel shut off valve. Impressive fabrication "Blue One"!
I had this problem with my Model A when the tank is full the fuel level is higher than the carb ( a float needle is not a shut off, only a fuel regulator at best] so I installed a tunnel ram to raise the carb up higher. It was less work than lowering the fuel tank in my case.
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