Fuel line check valve- draining issue

Whoa whoa whoa, the carb should not be dry after sitting a couple days. If it is, the carburetor is leaking fuel while it sits. Fuel drainback in the fuel lines will NOT siphon fuel out of the carburetor. The fuel inlet on the carb is at the top of the bowl not the bottom, so it would only suck air as the fuel drains back, the bowl would stay full of fuel.

Try this: Start the car and idle for just a couple minutes, THEN let it sit for a couple days and try starting again. If the problem is gone, then the cause must be fuel boiling out when the engine is hot when parked (I think it's very unlikely it would boil all the fuel out). If it starts hard like usual, you have a leaky carb, it's probably bleeding all the fuel out into the intake while sitting parked.

Originally Posted by Bailey28

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.

EVAP (Evaporative Emmissions) in the case of a carb, does not allow the fuel bowl to be vented directly to the atmosphere (done be eliminating the open vents we are more familiar with). But even if you have a later EVAP model, leaving the vent open (not having the EVAP plumbing intact and operative) has the same effect. The gasoline will simply evaporate over a given period.

Even the HOLLEY 1850C you mentioned has EVAP. Those were the two large hoses connected to the fuel bowls. It may become neccessary at some point to have a modified carb EVAP system on a street driven carb car as the formulation of gasoline keeps changing (especially the addition of alchohol) and is hitting four bucks a gallon.

Also make sure the float level is correct as if too low will exhibit like conditions.

Please let us know what you find for the archives (post to this thread).

Originally Posted by Motorhead

Whoa whoa whoa,

Reminds me of Yosmite Sam who shoots his horse after not stopping at his first command.

...the carb should not be dry after sitting a couple days. If it is, the carburetor is leaking fuel while it sits. Fuel drainback in the fuel lines will NOT siphon fuel out of the carburetor. The fuel inlet on the carb is at the top of the bowl not the bottom, so it would only suck air as the fuel drains back, the bowl would stay full of fuel.

Try this: Start the car and idle for just a couple minutes, THEN let it sit for a couple days and try starting again. If the problem is gone, then the cause must be fuel boiling out when the engine is hot when parked (I think it's very unlikely it would boil all the fuel out). If it starts hard like usual, you have a leaky carb, it's probably bleeding all the fuel out into the intake while sitting parked.

You have not come across fuel evaporation in carbureted cars yet?

Fuel will drain through the needle and seat if the seat is damaged or the float setting is incorrect.

To check for a carb leaking down (bad bowl plug or cracked housing), simply shine a lite down the carb throat soon after shutdown. If the plenum floor is wet or puddled, you have a leak-down.

This problem (evaporation) is very common on a LINC specific forum with AFB's.

Originally Posted by Motorhead

Whoa whoa whoa, the carb should not be dry after sitting a couple days. If it is, the carburetor is leaking fuel while it sits. Fuel drainback in the fuel lines will NOT siphon fuel out of the carburetor. The fuel inlet on the carb is at the top of the bowl not the bottom, so it would only suck air as the fuel drains back, the bowl would stay full of fuel.

Try this: Start the car and idle for just a couple minutes, THEN let it sit for a couple days and try starting again. If the problem is gone, then the cause must be fuel boiling out when the engine is hot when parked (I think it's very unlikely it would boil all the fuel out). If it starts hard like usual, you have a leaky carb, it's probably bleeding all the fuel out into the intake while sitting parked.

This sounds like a good idea to me. It would show that there is a fuel leak or it is boiling out on a hot shut down. Another option may be to pop the hood and try and get it cooled down quick after driving it. I pulled my car in one day when it was hot and heard a muffled sound like a drop of water dripping into a hot pan. I pulled the air cleaner and saw fuel dripping out the accelerator pump nozzle on my holley. After it cooled a little it stopped. I imagine it happened often but never caused a starting problem.

Originally Posted by KULTULZ

Reminds me of Yosmite Sam who shoots his horse after not stopping at his first command.

LOL Yosemite Sam huh. "All right, all right, I'm a thinkin'! And my head hurts."

Originally Posted by KULTULZ

You have not come across fuel evaporation in carbureted cars yet?

Fuel will drain through the needle and seat if the seat is damaged or the float setting is incorrect.

To check for a carb leaking down (bad bowl plug or cracked housing), simply shine a lite down the carb throat soon after shutdown. If the plenum floor is wet or puddled, you have a leak-down.

This problem (evaporation) is very common on a LINC specific forum with AFB's.

I haven't used a Carter AFB but I had an Edelbrock Performer on my 460 for a few years. Initially it had a hot-start problem that was solved with the 'phenolic' (wood) spacer, but I've never ever had a carb evaporate completely dry after a matter of days. I could let the Bronco sit for a week and it would still fire on the first crank. My pickup normally sits for weeks at a time out in the direct sunlight and summer temps, and it's always fired right up, never had a problem with it evaporating off completely. Granted, it has an electric fuel pump, but I don't give it time to fill the carb, I just put the key in and crank.

The needle and seat are located well above the floor of the fuel bowl on every carb I've ever worked on (Edelbrock, Holley, Quadrajet, motorcycle and other small engine carbs), making it impossible to drain the fuel bowls through the fuel inlet. You might be able to skim a little fuel off the top before the level gets down to the needle and seat, depending on the carb, but it would never be able to drain enough out to cause a no-start condition.

It could complete evaporation due to boiling like you're saying, but would have to happen before the engine cools off, because I still don't think 'normal' evaporation would drain the bowls in 3 days. In that case, if he waited anything more than a couple hours, he would have this condition. A leak, on the other hand, could take any duration depending on the severity of the leak. You may not be able to see anything out of the ordinary immediately after shutoff, and as soon as you crack the throttle open the accelerator pump will squirt making it impossible to find a puddle from the leak. The only good way I know of to check for a leak is to take the carb off the vehicle with it full of fuel and set it on a box or something to watch for the wet spot/drips. I could be wrong, maybe my inexperience with the Carter AFB is showing through here, but I was under the impression that they were more or less identical to the Edelbrock Performer carbs.

Originally Posted by Motorhead

I haven't used a Carter AFB but I had an Edelbrock Performer on my 460 for a few years. Initially it had a hot-start problem that was solved with the 'phenolic' (wood) spacer, but I've never ever had a carb evaporate completely dry after a matter of days. I could let the Bronco sit for a week and it would still fire on the first crank. My pickup normally sits for weeks at a time out in the direct sunlight and summer temps, and it's always fired right up, never had a problem with it evaporating off completely. Granted, it has an electric fuel pump, but I don't give it time to fill the carb, I just put the key in and crank.

Yes, but what year is the truck and does it have EVAP? The hot start problem was fuel percolation, boiling of the fuel in the bowl due to heat soak after shutdown. If she boils, it has to evaporate somewhat. Again, it depends upon the design of the carb and if any EVAP systems are used.

The needle and seat are located well above the floor of the fuel bowl on every carb I've ever worked on (Edelbrock, Holley, Quadrajet, motorcycle and other small engine carbs), making it impossible to drain the fuel bowls through the fuel inlet. You might be able to skim a little fuel off the top before the level gets down to the needle and seat, depending on the carb, but it would never be able to drain enough out to cause a no-start condition.

True. But a AUTOLITE 4100 or HOLLEY 4010 will have the needle/seat on the bottom of the fuel bowl and draining through the needle/seat is possible, especially with a defective check valve in the pump. On an AFB, if the fuel level either boils or say the fuel level is set too low, it will leave the needle/seat open after shutdown leading to the possibility of further evaporation. This will be compounded if the car is parked on a non-level surface.

It could complete evaporation due to boiling like you're saying, but would have to happen before the engine cools off, because I still don't think 'normal' evaporation would drain the bowls in 3 days. In that case, if he waited anything more than a couple hours, he would have this condition.

No, it would take a few days to evaporate completely and the pump would have lost it's initial prime, compounding the problem.

A leak, on the other hand, could take any duration depending on the severity of the leak. You may not be able to see anything out of the ordinary immediately after shutoff, and as soon as you crack the throttle open the accelerator pump will squirt making it impossible to find a puddle from the leak. The only good way I know of to check for a leak is to take the carb off the vehicle with it full of fuel and set it on a box or something to watch for the wet spot/drips. I could be wrong, maybe my inexperience with the Carter AFB is showing through here, but I was under the impression that they were more or less identical to the Edelbrock Performer carbs.

There would have to be a flaw in the casting (fuel bowl) to leak down at this rate. There is no plug at the bottom to leak as on a say ROCHESTER.

The EDELBROCK is the copy of the CARTER, manufactured by WEBER.

Take a small glass of oxygenated fuel and leave it outside for a few days and see what is left. Pump gas is now formulated for closed injection systems.

As for the leak itself, one would shine the light down the venturis before touching anything. A small accelerator pump shot would/should not disguise a heavily flooded carb. plenum.

Nice discussion...

Baily, glad to see this brought up - I've got the same problem with my 1408 Edelbrock on a 351w, aluminum intake'd Bronco - after sitting for say the weekend, you had to crank it long enough to refill the float bowl (or so it seemed) - an inordinate amount of time considering later that day or even the next day it'd start almost before I get the key all the way to the start position.


I think the EVAP system is the answer, I'm pretty sure the bowl vents should be routed to a charcoal canister so the fumes are captured and re-introduced on startup - the unfortunatel thing is with a standard air filter the bowl vent tubes stick up in the middle of the filter - I guess I'll try drilling holes in the filter base and running tubing (sealed of course) to the bowl vents and teeing them to the oem canister.

You know.... The vacuum in a fuel tank will drain the fuel lines but NOT the carb.

SO, if you think the fuel in the carb can actually evap over a few day's, (I don't) then this evap theory v/s the tank not being vented can indeed make it hard to start.

BUT!

I run this schitty gas in my 61 falcon 1V carb that's vented and even after sitting 2 weeks there is PLENTY of fuel in the carb to start it....

Boiling to evaporate it is what I am going to back up, boiling then a bit of vacuum in the fuel tank to help pull fuel from the lines back twards the tank....

Any creedence to my assumptions?

nope, no credence at all.


I think it's going out the bowl vents, at least dropping below the accel pump prime level -

FE, remember, we're talking AFB's here, not factory carbs like your 1bbl

I've had this issue ever since I built the motor/truck 14 years ago - it never occured to me to run a heat sink spacer, and I have not explored that avenue.

Honestly, I've just lived with it. But, since it's been parked for 2 years rusting quietly in the woods behind the barn When I dig it out at some point soon I will begin by delving into this mystery and hopefully reaching some conclusion besides adding a priming electric fuel pump.

I ran a genuine Carter AFB on my 75 F-250 Highboy with nary a problem...

I've ran several carter/edelbrock jobbers on my 85 ghia 302 with mechanical pump and return line back in 93/94 in HOT Southern Cal, never a problem (course the fuel was better 15 years ago...)

I'm just not buying the fuelevap after a couple day's or even a week and a half...

Bioling AND evap I can almost see, and maybe a little drain back through the needle and seat...

Fuel level isn't an issue if he can go FT in 1st through 4th.....

I'm going to watch for this in my shop this month... It's been 100* for most of the month.

FE