Fuel Pump?

[HighwayThunder]

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]

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]

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]

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]

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]

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]

Electric Fuel Pump

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]

Still Stalling!

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 again

Note 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]

What CFM is your carburetor.

John

[DKheld]

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.


Sounds a lot like my coil problem...
Eric

[scumdog]

#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.


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]

Coil sounds like a good place to look.

[Yadkin]

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 again

Note 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]

Good Advice

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]

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.




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.

Good idea to start with the coil.

Eric