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HighwayThunder
12-03-2016, 12:43 PM
My 390 FE has a hot cam, Street Demon carb. It's been trouble tuning it to optimum. It'd be running fine and then, for no apparent reason, stall. Restarting afterward would be problematic.

Had always thought that this was due to my inexperience in doing a proper tune-up. So I took the car to a shop specializing in performance engines and had them do the tune up.

When I picked the car up it ran better than it ever had before. It drove fine through the surface streets leading to the highway and then ran OK at highway speeds. But after about 10 miles, off the highway in stop-n-go traffic, it stalled again. It would restart but stall when put in gear. After several start-stall iterations, it wouldn't restart. Had to tow it home. The next day I got it started (using some canned starting fluid) and drove it a short distance.

Started it again a few days later. After a full warm up, it idled smoothly for about 5 minutes and then faltered and died.


Would the above description suggest a problem with the stock mechanical fuel pump? Or is there another possible explanation for it?


I compared the specs for the Demon carb and the stock fuel pump. The input fuel pressure range for the carb is slightly higher than the output range of the pump, but the nominal numbers do fall within both ranges. However, the pump is old. Have considered replacing with an electric pump.


Cheers,

jopizz
12-03-2016, 01:01 PM
I compared the specs for the Demon carb and the stock fuel pump. The input fuel pressure range for the carb is slightly higher than the output range of the pump, but the nominal numbers do fall within both ranges. However, the pump is old. Have considered replacing with an electric pump.


Cheers,

Specs on your stock fuel pump mean nothing. The only way to tell what your pump is putting out is to attach a fuel pressure gauge. You may find out that's it's not putting out anything close to what it's supposed to. Newer fuels and old pumps are a bad combination.

John

pbf777
12-03-2016, 01:34 PM
If you feel your fuel pump, or any portion/component of the fuel delivery system (to the carburetor) is at fault (including vapor lock), inspect the fuel level within the carburetor fuel bowl(s) immediately upon the vehicle's stalling.

Your Demon carburetor is equipped with either a sight glass for viewing or sight screw affixed to the fuel bowl which is removed for inspecting fuel level. Scott.

Yadkin
12-03-2016, 08:56 PM
I've had a lot of problems with mechanical fuel pumps available from local parts stores. Airtech units are inexpensive, look like OEM, so all the stores carry them, but steer far away from them. Buy a good brand through Summit or another speed shop.

Electric has the advantage of being able to wire to turn on prior to crank, filling your evaporated fuel bowls in the carburetor. But frame mounted pumps are noisy. In tank is the best way to go (I have this setup) but it requires modification of your tank with a large hole on the top and an access hole in the trunk shelf. Tanks Inc makes a bracket that will work, but has to be lengthened by welding. Make sure that you get a low pressure pump (5psi) with your carb setup.

pbf777
12-05-2016, 11:50 AM
I believe most of the "in-tank" electric fuel pumps will be of the E.F.I. intended application (35-50+ P.S.I.), but this is unimportant, as the resultant working pressure will be dictated by the fuel pressure regulator, which yes, should be set at approximately 5-7 P.S.I. for most carburetor applications, and of the "by-pass" design to reduce laboring the pump needlessly. Scott.

stubbie
12-05-2016, 08:02 PM
I would look at a Posi Flo facet pump if replacing yours. You can get a 1.5-10psi what they call a fast street version. They make a bit of a ticking noise when turned on but you probably wont hear it once the engine is running.

HighwayThunder
01-21-2017, 02:52 PM
Following up on the probable fuel pump problem I installed an electric fuel pump. The carburetor manufacturer suggested the Mr. Gasket Model 12S as meeting their flow specs. The new fuel pump solved the problem of erratic engine behavior and sudden stalling.

Here are some pics of the installation.

HighwayThunder
03-10-2017, 03:51 PM
I'm still having a problem with the car stalling for reasons mysterious. The scenario is the same:

The car starts.
After warm up, it drives great. I drive maybe 5-10 miles. Even in traffic, no problem.
I stop, turn the car off for a few minutes.
The car starts OK, but idle is suddenly lower than it was. It stalls when put in gear. Even if I give it some gas before putting it in gear, it stalls. Even after an hour or so of cool-down it still stalls. (It behaves like you'd expect it to if it had a vacuum leak, but it doesn't. )
I have it towed home
The next morning it starts right up and drives great againNote that the engine does not seem to be overheating. TempGauge stays in the normal range. Nonetheless, I do think that the problem is temperature related.

If I recall correctly, the themostat is 180 degrees. I'm going to replace it with one that flows at 160 degrees. (grasping at straws, here)

Could the carburetor be sensitive to a gradual rise in engine block heat?

I've been trying to figure this out for months. I'm flummoxed.

Cheers,

jopizz
03-10-2017, 04:00 PM
What CFM is your carburetor.

John

DKheld
03-10-2017, 05:08 PM
I've had 2 similar problems.

#1
'60 Tbird. Problem was the original gas tank - even though I had the OEM tank boiled and coated. Condensation finally took its toll and I decided to have the OEM tank cleaned and coated (and that tank was in pretty nice shape - car was bought new by my Dad and it's been garage kept all it's life). Replaced the steel line front to back too.
After having that done I also found that the ethanol in today's fuels was destroying the coating and it was coming loose.
Replaced the tank (MQ Products - Canada) and it worked better but still would seem to be starved for fuel at times. 2 new mechanical fuel pumps also. Wound up drilling a tiny hole on the side of the filler neck for air to prevent vapor lock. Before drilling I tried a different cap (vented) but it would let so much air in (and none back out) that the fuel would be pushed past the float needles. At times when I opened the cap it felt like I had 20-25 psi of air pressure in the tank. Since drilling the hole it's been fine. Re-used OEM cap. Drilled the hole on the side of the filler neck to prevent water from entering when washing. Would be just a drop or two but figured if I could prevent it - why not. Tank may rust sooner with the hole in the neck? All I really care about is that it works now and no more tow bills.

#2
'57 MGA These have a low pressure SU electric pump. Pretty much the same symptoms - turned out to be the coil. Would heat up and break down then work fine after cooling back off. Took a while to find that - never suspected ignition - always seemed to have good enough spark. Thought it was the carbs or fuel pump because I had rebuilt them. Shudda' known I do good work and it was something else. :D


Sounds a lot like my coil problem...
Eric

scumdog
03-10-2017, 06:52 PM
#2
'57 MGA These have a low pressure SU electric pump. Pretty much the same symptoms - turned out to be the coil. Would heat up and break down then work fine after cooling back off. Took a while to find that - never suspected ignition - always seemed to have good enough spark. Thought it was the carbs or fuel pump because I had rebuilt them. Shudda' known I do good work and it was something else. :D


Sounds a lot like my coil problem...
Eric

Sounds like the same problem I had with my '81 Harley.
Started up great when cold and ran well on the highway but at the first stop-light in town it would 'drop a lung" - run on one cylinder.
And when I stopped to gas up it was OK when cold, a bear to start when hot.
After trying different plugs etc I swapped plug leads - now the other cylinder dropped out and the dead one sprung to life.
Tried a new plug lead for the dead cylinder but no difference.
Checked the coil ( which was directly above the motor) and saw a hair-line crack.
New coil = no more problem.

stubbie
03-10-2017, 08:58 PM
Coil sounds like a good place to look.

Yadkin
03-11-2017, 07:29 AM
I'm still having a problem with the car stalling for reasons mysterious. The scenario is the same:

The car starts.
After warm up, it drives great. I drive maybe 5-10 miles. Even in traffic, no problem.
I stop, turn the car off for a few minutes.
The car starts OK, but idle is suddenly lower than it was. It stalls when put in gear. Even if I give it some gas before putting it in gear, it stalls. Even after an hour or so of cool-down it still stalls. (It behaves like you'd expect it to if it had a vacuum leak, but it doesn't. )
I have it towed home
The next morning it starts right up and drives great againNote that the engine does not seem to be overheating. TempGauge stays in the normal range. Nonetheless, I do think that the problem is temperature related.

If I recall correctly, the themostat is 180 degrees. I'm going to replace it with one that flows at 160 degrees. (grasping at straws, here)

Could the carburetor be sensitive to a gradual rise in engine block heat?

I've been trying to figure this out for months. I'm flummoxed.

Cheers,
Check the position of the high idle cam (passenger side of the carb), and your idle screw (driver's side). The high idle cam is stepped and you might be on the lowest step when the choke isn't hot. Then when it gathers heat it steps off the lowest step and your idle screw may be turned in too low.

HighwayThunder
03-11-2017, 01:41 PM
Thank ya'll for your experience.

Yadkin:

I've suspected the carb. It has been difficult to tune. Quite possible I've done it wrong. (Don't think it related, but spark plugs indicate mixture is too rich, even though needles turned in well below factory settings.) Will call Street Demon tech support and discuss with them.

jopizz:

625 CFM Street Demon. I installed the electric fuel pump that their tech support specified.

DKheld:

The gas tank's new and I coated it before install. What size hole did you drill in the filler neck? Did you drill the hole in the section of filler neck that's inside the trunk?

Will also take your advice and install new coil. Inexpensive elimination of a variable.

Cheers,

DKheld
03-11-2017, 09:58 PM
The '60 Tbird gas tank has a filler tube that sticks through the rear of the trunk via a big rubber grommet.

At the end of the filler tube the cap ring is welded to the filler tube and forms sort of a double thickness ring. I drilled my hole just past that cap ring in the single tube and right before it goes through the rubber grommet so the hole is basically under the license plate flap outside the trunk.

Here's a pic of the '60 tank but its laying upside down compared to how it would be installed in the car. Think you can see the double ring for the cap I am talking about.There is a little circular weld visible on the cap ring.


http://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/GasTank1.jpg

Used the smallest bit in the set I had which I believe was 1/16 - of course broke that one so went to the next size up which is 5/64. Don't know if it was a great idea but it sure works. :o

Good idea to start with the coil.

Eric

HighwayThunder
03-12-2017, 01:17 PM
Eric,

I thought it was not a factor but, given your proposed solution to the problem, maybe it was: Both stalling events occurred immediately after I had stopped to put gas in the tank.

Cheers,

jopizz
03-12-2017, 01:38 PM
Eric,

I thought it was not a factor but, given your proposed solution to the problem, maybe it was: Both stalling events occurred immediately after I had stopped to put gas in the tank.

Cheers,

Do you have a vented gas cap?

John

HighwayThunder
03-13-2017, 10:22 AM
No, gas cap's not vented. Should I just drill the hole in the cap?

It's dawning on me that vapor lock may have been the problem the whole time. I'm also planning to re-route the gas line, not so close to the engine heat, and insulate it.

simplyconnected
03-13-2017, 03:33 PM
No, gas cap's not vented. Should I just drill the hole in the cap?..NO! Your original cap was vented and your present cap should be, too.

You get two choices:
Vent the tank with a pipe that runs through your trunk and out the filler housing (outside) OR
Use a vented gas cap.

A small hole in your filler tube is NOT an option and is dangerous. These cars left the factory with no fuel issues. Get back to 'stock' and you will be good, so buy a vented gas cap. They don't cost much. - Dave

DKheld
03-13-2017, 05:02 PM
Oh - yea - forgot to mention. Didn't want to drill a hole in my cap because it was the original one.

http://media500.dropshots.com/photos/260234/20140211/161340.jpg

Don't believe the OEM cap was vented (at least on the '60)

When I tried a vented cap I used one similar to this although the tabs hit the license plate flap on the '60 (so I had to bend them down) plus it was a PITA to remove because the side tabs were not very big and that made it hard to twist.

http://i.ebayimg.com/images/g/O5AAAOSwGtRXxXsy/s-l1600.jpg


That filler neck hole - dangerous - probably....but think about this.....

The OEM 4100 carb has a vent hole on top directly above the front fuel chamber. If either of the floats in the carb stick open - the carb dumps the excess fuel on top of the engine right behind the distributor.

Fuel + heat + spark = Fire.

Yep - been there - done that
http://media5000.dropshots.com/photos/260234/20160330/b_184311.jpg

http://media5000.dropshots.com/photos/260234/20160404/111441.jpg

So I didn't think the small hole in the filler neck would be any more dangerous than the vent hole on the carb.

Figure if I see fire back there I'll just put the pedal to the medal and out run it.

:D

Eric

(definitely use the hole in the filler tube as a last resort though - hard to fix except maybe with JB Weld)

simplyconnected
03-13-2017, 05:49 PM
My post assumed you have a Squarebird but the information I gave about venting still stands. You don't want a pressurized gas tank, ever.

New cars draw a vacuum on the fuel tank to make sure there is no pressure. They capture and burn those fumes, not because the smell of raw gas is nasty but because it is explosive.

Your fuel tank should never produce so much pressure that it blows gasoline past your carb's needle valves. Remember, the fuel line delivers liquid gasoline, not fumes. Those little floats cannot stop more than six pounds of pressure, otherwise they spew into the bowls, out the vents, and onto your hot engine.

If your tank is not vented, to prevent pressure buildup use a vented gas cap. - Dave

HighwayThunder
04-14-2017, 02:08 PM
Here's a pic of the new fuel line. It's up off the engine and insulated from the heat. Nonetheless after warmed-up and then turned off, the car will stall after restart.

What I've noticed is that when that happens, the fuel filter will not fill, even with just the fuel pump on (refer to 2nd pic). My theory is that the unfilled part of the filter is a pressurized vapor keeping the filter from filling with liquid.

What about the carburetor? Could it be I need to put a thermal block between the carb and the aluminum intake manifold?

jopizz
04-14-2017, 02:28 PM
Did you ever get a vented gas cap. Remove the cap to relieve the pressure and then see if it will pump.

John

scumdog
04-14-2017, 06:57 PM
Here's a pic of the new fuel line. It's up off the engine and insulated from the heat. Nonetheless after warmed-up and then turned off, the car will stall after restart.

What I've noticed is that when that happens, the fuel filter will not fill, even with just the fuel pump on (refer to 2nd pic). My theory is that the unfilled part of the filter is a pressurized vapor keeping the filter from filling with liquid.

What about the carburetor? Could it be I need to put a thermal block between the carb and the aluminum intake manifold?

I doubt your theory re the 'pressurised vapour' however in any event I would have put the filter on that vertical section of fuel line above the fuel pump.
If it WAS vapour under pressure in the filter it would vent itself through the carb as soon as the fuel in the fuel bowl dropped its level.

I also doubt the necessity to put in a thermal block.

My 2 cents worth.

stubbie
04-15-2017, 09:50 PM
I see Street Demon carbs need a bigger accelerator squirt nozzle when using larger cams and more cubic inches. The standard nozzle is .031 in size. Some of the symptoms you describe are caused by the above nozzle or bad vacuum.

HighwayThunder
04-27-2017, 12:29 PM
I noticed that my feed tube to the fuel pump is 5/16". The main tube running under the car is 3/8", and the new tube I installed over the engine is 5/16". I mentioned this to an ME as a possible cause of the problem. He immediately suggested it could be a cavitation problem.

"The cavitation phenomena occur in regions where large pressure drops results in the local pressure falling below the vapor pressure, resulting in formation of vapor bubbles. Typically for pumps, cavitation occurs in the suction side of the pump blades, which in turn results in a reduction of effective area of the blade, thereby diminishing the efficiency of the pumps."
(SAE, Predicting cavitation in fuel pumps, 03-Jan-2014, http://articles.sae.org/12709/)

Causes of Cavitation:
"Having the pump at too high of a distance above the fluid source
Having too small of a diameter of suction pipe
Having too long of a distance of suction pipe
Having too many fittings on the suction pipe
Handling a liquid with a low vapor pressure
Running the pump too fast"

(Dale Conway, Pump cavitation diagnosis and control, 2/18/2010, http://www.flowcontrolnetwork.com/qa-pump-cavitation-diagnosis-control/)


I'm going to replace the 5/16" tubing with 3/8" and re-test.

Cheers,

simplyconnected
04-27-2017, 05:48 PM
You don't have cavitation, or vapor lock. OEM fuel pumps are diaphragm-type so there is no high speed vanes or blades. We never heard a word about taking John's suggestion in regards to the tank cap. Aside from all that, your car and millions of others worked perfectly fine from the factory and for many years.

You MAY have:
A restricted pickup screen,
A collapsed fuel line,
A pinched fuel line,
Carb issues.

Your engine will run around town nicely with a 1/4" fuel line. - Dave

OX1
04-28-2017, 09:36 AM
What about the carburetor? Could it be I need to put a thermal block between the carb and the aluminum intake manifold?

No it does not. I've run these exact carbs on large mud trucks
that the radiator is clogged with mud, truck was pushing 230 and
have had zero problems with heat from the carb.

Get a cheap electric fuel pump and mount it right in front
of fuel tank. I did this due to the "pushrod" that is required
for the funky 430 fuel pump actuation.

If you want fuel lines to look authentic (on the 430, the
upside down fuel pump on top front of engine is a nice
conversation piece), you can run fake lines (I did) in
and out of pump and "hide" real fuel line coming up back of engine.

BEVS BIRD
04-29-2017, 04:05 PM
HIGHWAY Thunder,, still stock ignition?? sounds like condenser prob or if electonic , bad ignition module..if you still suspect fuel related,,,you MUST put guages on and t/shoot that system completely. This type of prob can drive you to selling car and the growin Roses for a hobby CHEERS TERRY

simplyconnected
04-29-2017, 06:05 PM
...What I've noticed is that when that happens, the fuel filter will not fill, even with just the fuel pump on (refer to 2nd pic). My theory is that the unfilled part of the filter is a pressurized vapor keeping the filter from filling with liquid...
http://www.squarebirds.org/vbulletin/attachment.php?attachmentid=13896&stc=1&d=1492188812

Your float bowls are vented to the carb throat. The floats only close-off supply when enough LIQUID gasoline lifts the floats. A constant flow of gasses will simply vent out past the needle valve as it remains open until the float closes it. - Dave

HighwayThunder
05-02-2017, 09:54 AM
You don't have cavitation, or vapor lock. OEM fuel pumps are diaphragm-type so there is no high speed vanes or blades. We never heard a word about taking John's suggestion in regards to the tank cap.

I did install a vented cap and had the same problem. (I also drilled a tiny hole in the [previously un-vented] locking cap to allow venting.)

Aside from all that, your car and millions of others worked perfectly fine from the factory and for many years.

...which makes it all the more irritating.

Cheers,

simplyconnected
05-02-2017, 05:20 PM
...which makes it all the more irritating...If you know OEM parts work when fitted properly, the only thing left to do is proper troubleshooting and maintenance. This issue does not require re-engineering or parts that are different from 'stock'.

Start troubleshooting by opening the fuel line and cranking the engine. If you get fuel, good. If not, check the pump and line back to the tank.

HighwayThunder
06-05-2017, 11:26 AM
The vapor lock problem continues despite my measures taken to abate it. This is a summary of actions taken so far:
Made all fuel lines the same diameter tubing (3/8”)
Routed fuel lines above and away from the engine and insulated them·

Installed a carburetor heat shield·

Replaced the 195F thermostat with a 160F thermostat
Replaced the mechanical fan with a shrouded electric fanI think it’s safe to assume that the continuing problem is still related to heat, with pressure and fuel flow rate assisting factors. With that in mind, there are two solutions that may alleviate the vapor lock.
During idle, fuel is not moving quickly through the lines nearest the engine, giving the fuel time to absorb heat. My electric fuel pump does not have a return line to the fuel tank. Putting an overpressure regulator near the carburetor with a return line back to the tank would allow fuel to flow at a near constant rate, reducing the amount of heat absorption in the line. ·

The PCV valve is connected via the carburetor rather than the intake manifold. I suppose it’s possible that the carb is pulling heat in through that connection. I plan to reroute the PCV to the intake manifold as a precaution.Comments appreciated.


Cheers,

simplyconnected
06-05-2017, 02:42 PM
All your changes are wonderful but NONE of them address the real problem which is, 'why isn't gas getting to the carb?'

You can prove your system very simply and in the comfort of your own garage. Invert a hanging soda-pop bottle filled with gasoline and vented, with a temporary rubber hose connected to your carb's inlet. Gravity feed works just fine, especially when the engine is not under load. You can still rev, which makes your mechanical fuel pump go faster.

The disconnected fuel line you removed simply goes into a gallon gas can. It's ok to extend the original line so the gallon container can sit on the ground because there is zero flow resistance at the end of that open hose.

Start your engine and watch. Even at idle speeds, flow shouldn't take long to fill a gallon container. When you rev the engine the container will fill faster with a mechanical pump but your electric pump will be steady. Tell us how long it takes your pump to fill a gallon container.

This test removes all possibility of heat-related and it reveals pressure-related issues. You should see gas gushing out. If you don't, test for restrictions, in small steps, all the way back to your fuel tank. From here in Michigan, I cannot tell if you have a hose that has collapsed from the inside or a fuel tank pickup that is clogged. YOU have to find those issues by employing sound troubleshooting techniques instead of throwing parts at a problem. We already know that working 'factory' systems performed well on many thousands of Thunderbirds like yours. - Dave

HighwayThunder
06-06-2017, 12:01 PM
Gas gets to the carb just fine while the car is warming up. It is after idling at temp for about 20 minutes that it stalls. The car did that with the old mechanical fuel pump and it does it with the new electric fuel pump. So I think I've eliminated the fuel pump as the culprit. I've replaced most of the fuel lines (but as stated, gas gets to the carb just fine while the car is warming up, so no kinks or restrictions in the lines).

What's left is a correlation with increasing heat.

Outside of the fuel system, a possible cause could be temperature-sensitive ignition components.

Cheers,

simplyconnected
06-06-2017, 05:30 PM
I agree that high temps can have an affect on your ignition coil BUT fuel delivery and ignition are totally separate issues that can be proved independently.

I'm still not convinced you have a vapor lock problem because it is rare, moving fuel under positive pressure would need a lot of heat (that we don't have) and your carb has floats that open until liquid fuel closes them. Otherwise, the float bowls are vented to your engine-side of the carb.

I thought we were addressing this issue:

http://www.squarebirds.org/vbulletin/attachment.php?attachmentid=13896&stc=1&d=1492188812

Now you say, it's getting gas. Is it or not? Idle speeds do not drink much gas. When this fault shows up, can you pump the throttle while watching for a squirt of gas? No, you don't need to stick your face over the carb if you use a mirror and a light. If you see squirts of gas, you don't have a fuel problem.

If you think your coil is causing problems, while the problem occurs pull a spark plug wire and plug it into a spare spark plug, laying on the intake manifold. It's better if you do this at dusk and outside. What does the spark look like? Do you hear it 'snap'? Is it pretty blue, or orange? If it's orange, temporarily swap with another car's coil. I don't care if the temporary coil is for a six cylinder, it should work. Are you still using a condenser, and is your points plate grounded? - Dave

HighwayThunder
06-11-2017, 02:04 PM
I think the epic saga of the stalling car has finally come to a finale.

Yesterday I rerouted the PCV line from the carb to the intake maniifold.

I also moved the the heater hose from a place where it was touching the fuel line near the carb (see photo). Later on that day I visited a car show (every second Saturday in Tucker, GA main square). A teenager restoring a 66 Mustang said he'd had the same problem with vapor lock and had traced it to the fuel line in contact with the heater hose. (!)

This morning when I tested the T-bird the problem seems to have gone. It ran for about 20 minutes without stalling. Temp stabilized at about 190F. Turned the car off. About 8 minutes later the engine restarted. Ran steadily at idle speed with no power loss.

I'm so thrilled to be able to drive the car without fear of being stranded and towed.

I hope this thread will be of benefit to anyone dealing with a similar enigma.

Thanks to all of you for being part of the process. This forum is a fabulous resource. I only hope that I can contribute in kind.

Cheers,