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471A
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In 90 degree heat, after an hour in stop and go traffic, the 355 SBC in my 29 Model A began loading up when stopped at traffic lights, stalling when starting to move, then ultimately shutting off completely. For intake, the engine runs two Holley 600 carbs, a Holley electric pump, and a Weiand/Holley 250 blower. When I restarted the engine 15 minutes later, it belched blue smoke, evidencing flooding. Fuel pressure never went about 5.5 pounds and I had only been ightly feathering the throttle. We discovered the cause of the flooding after first removing the air cleaner on the carb closest to the firewall. While my friend Steve cranked the starter, I, being careful to look at an angle so as not to get burned by a possible backfire, watched fuel flow into the carb. Fuel was gushing, not just dripping, into the rear carb from the gas tank vent. The vent is plumbed from the tank to route any overflow back into the engine, and not dangerously onto the exhaust or electricals near the gas tanks. There are two tanks, joined by a crossover tube, installed alongside of, but shielded from, drive shaft and each tank has a vent. The current vents are, however, located at the front of each of the two tanks and, since the A has about a 6 inch rake, the vents are not at the highest possible point. We plan to install vents at the rear of the tanks, and at the highest point. Any thoughts or suggestions are welcome. Thanks.
 

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Revolution Calling
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916 Posts
Blue smoke is oil.

Fuel pressure seems right. Gas 'tanks' vents should not be plumbed to carbs IMO. Needle and seat with a piece of trash in it can cause this same problem. Make sure there is a quality low micron fuel filter after all fuel system components as close to each carb as possible.

Many other variables here.

Watch that Steve guy, he's trying to burn your eyebrows.
 

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471A said:
In 90 degree heat, after an hour in stop and go traffic, the 355 SBC in my 29 Model A began loading up when stopped at traffic lights, stalling when starting to move, then ultimately shutting off completely. For intake, the engine runs two Holley 600 carbs, a Holley electric pump, and a Weiand/Holley 250 blower. When I restarted the engine 15 minutes later, it belched blue smoke, evidencing flooding. Fuel pressure never went about 5.5 pounds and I had only been ightly feathering the throttle. We discovered the cause of the flooding after first removing the air cleaner on the carb closest to the firewall. While my friend Steve cranked the starter, I, being careful to look at an angle so as not to get burned by a possible backfire, watched fuel flow into the carb. Fuel was gushing, not just dripping, into the rear carb from the gas tank vent. The vent is plumbed from the tank to route any overflow back into the engine, and not dangerously onto the exhaust or electricals near the gas tanks. There are two tanks, joined by a crossover tube, installed alongside of, but shielded from, drive shaft and each tank has a vent. The current vents are, however, located at the front of each of the two tanks and, since the A has about a 6 inch rake, the vents are not at the highest possible point. We plan to install vents at the rear of the tanks, and at the highest point. Any thoughts or suggestions are welcome. Thanks.
Unless this is set up with an emissions legal system, the tank vents should go to the atmosphere as directly as possible, they should never vent into the air cleaner, carb, or intake without using the charcoal cannister and control valves of a factory emissions system.

The tank vents should come off as high as possible, which can mean a vented filler cap, a tube tapped into the fuel fill pipe, or from the top of the tank usually at the fitting holding the gauge sender. If using a vent tube, it should be routed clear of hot zones and electrical components and end in such a way that any overfill or condensate runs on the ground clear of vehicle structure.

You also need to take the precaution of not filling the tank to its max capacity. If you run the fuel level up the filler pipe and that level is higher than the vent, fuel will run out the vent. In the good ole days of factory atmospheric vents, often the vent line was routed with a loop somewhere that rose higher than the fill pipe to prevent an overfilled tank from puking gas on the ground.

My recommendation is to run a vent line straight to a location higher than the tank, making the tank connection the lowest point before a loop which then vents to atmosphere somewhere near the back end of the vehicle. This puts the line in such a way that it will naturally drain back to the tank and not form puddles in the line. Also, inside the tank, the vent should end at the top surface of the structure, never hanging into the fuel. If the inlet to the vent is lower than the highest fuel level, overflow could start a siphon that would drain fuel till the level in the tank was lower than the intake of the vent.

Dual tank feeds should be joined thru a control valve that positively shuts one or the other tank off till needed. This stops cross feeding when fueling and when parked sideways on an incline, both of which can lead to excess fuel being accidentally and unnecessarily being vented on the ground.

I'd also recommend a drive shaft loop being used under the front part of the drive shaft, should a U-joint fail, this will prevent a situation where the loose end of the the shaft gets jammed into an adjacent fuel tank.

Bogie
 
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