[parsival]

Hi there,

To avoid the gas to run back into the gas tank,
I bought an inline check valve.
Who can tell me where to mount it.
I've got 3 connections on my fuel pump. 1 inn, 1 out. But
I don't know what the 3rd is for. Look likes it runs back to the gas tank.

Anybody ???

[Joel Koontz]

I'm not sure that you need, or want, a check valve on a stock type fuel system.

I am not aware of stock systems using them, at least not in the 60s/70s.

When the car is shut off, the fuel in the lines can heat up. If the fuel is prevented from going back to the tank it may cause pressure to build up in the fuel line and force fuel through the carb inlet valve.

[HJones1313]

Originally Posted by Joel Koontz

I'm not sure that you need, or want, a check valve on a stock type fuel system.

I am not aware of stock systems using them, at least not in the 60s/70s.

When the car is shut off, the fuel in the lines can heat up. If the fuel is prevented from going back to the tank it may cause pressure to build up in the fuel line and force fuel through the carb inlet valve.

+2, the vapors are designed to be returned to the tank, and then there's the charcoal canister, which I think is vented.

[lust4speed]

Mechanical pumps are based on a diaphragm and check valves - so they are already in place. Most of today's problems are with the fuel just percolating off.

Even with the vapor return, the pickup for the return is at the very top of the chamber inside the mechanical pump, so in theory the cavity would remain full of fuel.

[parsival]

Thank you,

But how do I avoid the gas to run back in the gas tank if the check valve in the fuel pump does not work properly anymore.

[Icefan71]

Originally Posted by parsival

Hi there,

To avoid the gas to run back into the gas tank,
I bought an inline check valve.
Who can tell me where to mount it.
I've got 3 connections on my fuel pump. 1 inn, 1 out. But
I don't know what the 3rd is for. Look likes it runs back to the gas tank.

Anybody ???

Your fuel pump has an inlet, outlet, and a return to the tank.
Why are you worried about fuel running back to the tank? Is the motor hard to start?
And please give us some details about your car and motor.

[dmac]

Fuel remaining in the carb bowls should not be draining back, and should be enough to strat the motor and keep it running until the mech pump 'catches up' and fills the line again. Unless you have installed larger diameter fuel lines, which take longer to fill up.

[68 Firebird]

Agree with dmac. My Q-jet will spin for a second and fire even if sitting for a week.

Gerry

[lust4speed]

Originally Posted by parsival

Thank you,

But how do I avoid the gas to run back in the gas tank if the check valve in the fuel pump does not work properly anymore.

If the fuel pump isn't working correctly, then instead of getting a full pump each engine rotation, the flow would be reduced enough to really add to the time it takes the fuel to get up to the carb. Not to mention that your fuel pump might not be keeping up with full throttle blasts. An additional check valve wouldn't do anything to help an ailing pump.

I think that my manual pump equipped car won't go a week before it has to spend extra time pulling fuel up from the tank - and that's with a new fuel pump and good lines. Today's gas just evaporates quickly. Sometimes my car doesn't get started for several weeks and I got tired of abusing the starter. I added a small pusher pump (pulsar pump) at the tank so I could fill the carb before hitting the starter. It works great and I turn the pump off before hitting the road. I can always leave it on if I need a little additional boost. These small pulsar pumps work just like a mechanical fuel pump with a diaphragm and check valves. Here's an example of the pulsar pump: Mr. Gasket pump. This setup works fine for moderate horsepower requirements. My cruiser has 298 horsepower at the rear wheels, and the system has no problem keeping up with it. If that figure was 400 at the rear wheels, then a different system would be needed. Also the pulsar pump is really the only pump you can pull fuel through when it is off. the rotary and gerotor designed electric pumps won't pass fuel.

[parsival]

Thanks for your replies.

I will consider an electric pump.

Arno

[Jon Salem]

Parsival,

Didi you resolve the issue? I have a 71 Lemans Sport w/400/4BBL and after 3 days have to cracks and crank or throw some fuel down the throat. Runs fine otherwise. A mechanic mentioned a bas check valve.......Thanks.

[tom s]

Just have a can of spray carb cleaner around and shoot some in with the throttle open.No need to have gas around.Tom

[MidnightAuto]

Gas does evaporate fast. I put a check valve in and it did help in summer. I am still considering a pusher.

[Jon Salem]

Thanks. I was hoping that a fuel pump with a built-in check valve was available.
Any recommended check valves?,

[MidnightAuto]

I used a Dorman check valve.

U can also check out fast Monty garage on YouTube and watch the video on hard starting

[Formulajones]

A stock mechanical fuel pump works off a diaphragm and check valve setup as already mentioned earlier in this thread.

So technically it should hold fuel from the pump forward. If not I'd look at another mechanical pump.

Your carb should also hold fuel in the float bowl, enough to fire off fairly quickly with minimal cranking, and should run on that long enough for the fuel pump to catch up and run normally.

I've never had an issue with todays fuel evaporating completely out of the carb float bowls. If it's bone dry it must be leaking somewhere, or the carb has gotten so hot it's percolating off, or maybe pushing it past the needle and seat after shut down.

Some of my carbed stuff that I'm not driving can sit for months and they still have a shot of fuel from the squirter and fuel in the bowls. It'll run on that for a several seconds and then I see fuel pressure build as the mechanical pump catches up.

[Sirrotica]

Just an observation after being into dozens of carbs over the last 50 plus years, once the fuel is in the float bowl, it doesn't exit through the fuel line. Most carbs fill from the top, and once the fuel is in there, it can't siphon back. In the case of a Q Jet the seat is submersed in fuel, but Rochester designed an anti siphon check valve that fits into the filter in the fuel inlet nut. Even still, it won't empty the bowl, but it could drain it maybe half way, at most.

Holley fills from the top, as do the majority of Rochester carbs, and the Carter carbs. I'm failing to see how fuel siphons out of the float bowl?....

[Schurkey]

Originally Posted by parsival

But how do I avoid the gas to run back in the gas tank if the check valve in the fuel pump does not work properly anymore.

Originally Posted by Jon Salem

I was hoping that a fuel pump with a built-in check valve was available.

Get a fuel pump that doesn't have defective check-valves.

HOW do you know your fuel pump check valves are defective? Be specific.

[Kenth]

From 1976 Pontiac Service Manual:

"A new design fuel filter with integral check valve to meet Federal safety regulations for fuel loss during vehicle roll-over."

This would stop fuel draining from fuel tank to the ground thru the carb at roll-over, not so much draining carb TO the fuel tank.

FWIW

[Trevor78]

Doesn't understand the issue to explain to others to help, so starts looking at electric pumps. That's how cars end up with Holleys, multiple layered old issues with new issues.