Fuel line check valve- draining issue

Has anyone here ever used a fuel line check valve, basically a one way valve on their fuel system?

I think I need one... here's why:

I am using both the old feed and return lines in my 86 mustang as new feed lines. I plumbed both 5/16" and 1/4" hoses to the bottom of my tank inside after removing the electric pump.

I combine both smaller hoses by way of a T-block to one 3/8" line under the oil pan of the car, then plumb that into a fuel filter, then into the inlet for the fuel pump. I am using the expensive Carter street/strip pump set at 6psi. I have a gauge near the carb that reads 4-5 at idle, 6-6.5 above that.

From there, I have about 5 feet of 3/8" line going to the left fenderwell, then along the upper firewall, then comes forward to the Carter AFB inlet feed.


MY issue is this: If the car sits for more than 2 or 3 days without running, it is very hard to start. It is not flooding, but it seems like it isn't getting any fuel. It is like I have to crank for 3 10 second intervals at least before I get it to run. After it starts it is fine all day, and even for a day or so after that when cold. Hot starting is fine. All systems are new, battery is new and the mini starter is turning the hell out of it.


I saw online that they make fuel "check valves" and wanted to try one in the system near the fuel pump and see if it is a fuel drain back issue.

Now this is the strange part: I do believe that fuel is still sitting in the bowls when I turn off the car, unless it percolates into the intake, then after sitting for a few days evaporates leaving the carb bowls dry or low on fuel. Then with the fuel draining back, I'm guessing it is like I am re-priming the fuel system each time I cold start the car.

You-all's thoughts?????

sounds like your boiling the bowls dry and repriming them. iron intake? might need a phenolic spacer. do you have a hot air stove on the exhaust that could be making it worse if the flapper is stuck.

I have an 86 Mustang GT, Edelbrock aluminum RPM heads with no heat crossover. Aluminum stealth 8020 intake, the Mr Gasket aluminum heat spacers under the carb, then the carb with an open element Moroso air cleaner.


If the gas inside the bowls boils, is it worth a damn after it does this, even if it is left in the bowls? By boiling, does it all come out? I solved most of the heat soak issue by going to the spacers. The cold start issue was always there.

those check valves really are not designed to be placed in the feed line. They are for keeping the fuel in the tank in the event of a roll over. They Will sacrifice your fuel flow. Just do it right and replace the hard line in your tank and run the appropriate line forward

I take it the pump you mention is mechanical. If so it should have a
non-return valve inside it .

Hold a sec... You're NOT running an injected car on a mechanical fuel pump are you?
Or is it throttle body injected ?

Anyway... Gregaust is right the fuel pump has a built in one way valve....

You are going to have to (IMO) run 3/8" from the tank to the mechanical pump. The filter needs to be after the pump (along with some type of filter on the pickup). Today's fuel evaporates much more quickly as it is designed for fuel injection and closed EVAP systems.

An electric pump at the tank will solve all the problems.

Ok let me clarify this,

The car is an '86 converted to a mechanical pump system with a carburetor. The entire engine was rebuilt. I don't have any heat risers, crossovers, etc.

Simple carb, intake manifold, heads, headers.

The two fuel lines 5/16 and the 1/4" run parallel to each other continuous from the tank to the T-block. After the T-block it is 3/8" to the in line filter, a Professional products aluminum sintered bronze deal. From the filter it goes into the Carter mechanical pump, driven by the camshaft eccentric. Then out from the pump to 5 feet of rubber line, then to a Jegs pressure gauge, then 6 more inches into the Carter AFB carb. I have a 3/8" banjo fitting on the carb.

When the car is running, it runs great. I get no fuel starvation issues even after a long 1-4 blast. Hot start is better now that I put the plates under the carb.

If the fuel pump has an anti drain back valve, then would it matter if I ran one, two, four, or seven feed lines to a T - block then ran 3/8" into the pump if it doesn't drain back to the tank? I used the old EFI return line also as a feed line to supplement the stock 5/16" original feed line. I think it is an ingenious idea! Instead of having to run one 3/8" or larger line, the two parallel lines run in tandem to feed the fuel pump.

After shutting off the engine, the rubber fuel line between the pump and carb is soft as I can squeeze it together. Someone was also saying that fuel that has been boiled is worth nothing after it does. If it boils in the carb, then sits for a few days, would this fuel even be lighting under compression and spark? Or am I pumping all this through the motor then it fires when I get fresh fuel from somewhere else in the system?

I ran the Carter / Edelbrock carb for the ease of tuning an mileage. I get great mileage, and it runs strong. I just don't like the heat soak issue I seem to be having. It's like I need a hole in the hood just to keep the carb happy.

Originally Posted by KULTULZ

Today's fuel evaporates much more quickly as it is designed for fuel injection and closed EVAP systems.

An electric pump at the tank will solve all the problems.

Whether the fuel in the bowl boils or not, it is evaporation of the fuel in the bowl that is causing the hard start problem after sitting a few days.

The fuel evaporates into the atmosphere (via the bowl vents).

A quick start is not possible as the fuel needs to be replaced by the pump.

The mechanical pump is drawing fuel (or attempting to) through two supply lines and a filter (should be on pressure side).

The mechanical pump does have an anti-drainback valve but it will not hold that pressure more than a day. It depends on a quick start with the fuel in the carb bowl to reprime.

Either you are going to have to modify the carb with an EVAP system or use an electric supply pump (with or without the mechanical pump) to overcome this problem.

Your vent system seems to have been unaffected by this modification.

Most of this is caused by today's reformulated gasoline. It is not blended for carburetion any longer.

Thank you guys! I will move the filter to the pressure side of the fuel line. Forgive me, what is an EVAP system? Emissions related? the Carter carb does not have a bowl vent like some of the earlier ones did that open to the atmosphere. I had one that had a large rubber flapper valve on the right side, but got rid of it.

I am agreeing with you all that there is an evaporation issue, which is why I thought the check valve would help out a little. As in if I could keep fuel in the line up to the carb, then the bowl would be the only thing I would have to fill vs. a 5 foot line and the bowl. Hence, I think it would start sooner. Kultulz, the fuel vent line is still in place unmolested at the top of the tank. I don't get any hissing or suction when I open the gas cap like negative pressure, etc.

I guess an electric pump in line with one of the hoses near the tank would get rid of the issue.

I guess in the mean time, I could run the fuel line higher along the firewall at one point to discourage drain back to the pump/tank. I could also check to see if the accel pump will shoot fuel after a few days.

This newer "blend" of gas sucks for us carbureted guys, kind of forcing us to use a electric pump. The last time I had a carbureted car was a '79 mustang in 1992 with a Holley 600 01850-C. Not the best carb, but I didn't have this issue.