Fuel Fluke

-
OK...... I removed the plastic fuel filter that's right before the carb to a steel one. I ran a hose off of the mechanical fuel pump into a gas can..... same results! This time the car started running rough and just about cut off... the temperature at the time was 195* and the fuel pressure was right under 5 psi. When I first cranked the car the pressure was at 7.5 psi or shade less.

The fuel pump feels cold compared to the engine. The hose between the fuel pump and carb is wrapped with heat protection and the electric fan is blowing on it like crazy!

If I have low pressure before the carb wouldn't that rule out the carb?

If anyone has suggestions I would appreciate it!
 
Whew! This is a tuffy. Keep at it. I can't add anything but it seems like a right track kind of thinking to me. Post #8 & 9 are very good.
I think I would try a new pump.
 
rumblefish360 said:
Whew! This is a tuffy. Keep at it. I can't add anything but it seems like a right track kind of thinking to me. Post #8 & 9 are very good.
I think I would try a new pump.
Click to expand...

I've by-passed the electric pump and still have the problem but I have not by-passed the mechanical pump(I can't believe the brand new Carter pump is already bad)... I have forgot to do that for some reason. Thanks rumble for reminding me... LOL

I'll try that tomorrow.
 
No problem. Even new mechanical parts can be bad or fail fast. It happens and allways sucks when it does.
 
I have a few thoughts..

A mechanical pump has very little in terms of "suck" to it. So IMO, start with basics. Is your tank or gas cap is vented properly? (easy tet is pull the fuel cap after it's been running a while. If you hear the hissing of air entering, it's not vented well enough...)

Pulling thru an electrc is not a good idea. If you need a pusher pump (the elctric is out back by the tank, correct?) then run it all the time. Although if you have an electric, I would not have bothered running a mechanical at all. The block off's cheaper than a pump :D.

The routing of the line is odd. IMO, it should not ever go up over the inner fender bulge and then down to the pump. You are asking for air bubbles in the feed side that way. The heat is a non issue. If there is 1.5" of air there, it's not picking up any heat from the headers and you placing a finger on it and feeling cool is the indicator. The fuel inside will be no hotter than the outside of that line.

The fuel all inside the carb bothers me. Because any carb that is starving will be dry in there. Kinda makes sense, no? No fuel inside the bowls = no fuel...

It should not be idling as high as it is. I dont know the package or your tuneup. But if the thing hangs up at 1100, your ignition curve needs some work. If you can't get it to idle at 800 or less, especially with a stick, your carb needs work after you fix the distributor.

I think it's a combination of these that are giving you fits.
 
No answers but a couple of thoughts. BTW, I had that same Summit inlet fuel line until recently. Nice piece but I had trouble with one of the flares sealing.

I've got a Carter mechanical pump. If I remember it was the strip version but without a regulator the needle bounced like crazy and it tended to overpower the seats in the carb. A regulator got both of those problems under control but I did notice that after time, while running, the gauge read lower and lower yet the bowls remained full.

I would try adding a regulator ( http://store.summitracing.com/partdetail.asp?part=QFT-30-803&FROM=MG and did include a mounting bracket) and reset the float levels. This regulator is preset at 6.5 psi. 7 and over you risk overpowering the needle and seat. Don't waste time with the parts store regulators with the dial on them.
 
Theres a pair of good thoughts.
I'm with Moper on the fuel line. Odd routing. It did leave a question mark in my head as to why that way. OE runs the frame rail preety far up to the pump.
Heat in the carb was a wonderment in my head.
 
Is your tank or gas cap is vented properly?
Click to expand...

I have been running the car with the gas cap open and still getting a massive drop in fuel pressure.


Pulling thru an electrc is not a good idea. If you need a pusher pump (the elctric is out back by the tank, correct?) then run it all the time. Although if you have an electric, I would not have bothered running a mechanical at all. The block off's cheaper than a pump :D.
Click to expand...

The elec pump was already on there when I bought the car... it's a small cheap pump. I just got done bypassing the mech pump and just using the electric pump..... it only pushes 4 psi and when the motor is held at a sustained RPM it drops to 3 psi... that's not going to cut it... so I just shut the motor off.





The routing of the line is odd. IMO, it should not ever go up over the inner fender bulge and then down to the pump.
Click to expand...

I just copied what was on the car when I bought it. Where does the line usually run when it enters the engine bay area? I wouldn't think it should go between the shock tower and the headers.



It should not be idling as high as it is. I dont know the package or your tuneup. But if the thing hangs up at 1100, your ignition curve needs some work. If you can't get it to idle at 800 or less, especially with a stick, your carb needs work after you fix the distributor.
Click to expand...

It only idles at 1100 when I'm having the vapor lock problem or whatever it is that's causing it. The curb idle is around 900 RPM is what I got it set at.


70Duster440 said:
I've got a Carter mechanical pump. If I remember it was the strip version but without a regulator the needle bounced like crazy and it tended to overpower the seats in the carb. A regulator got both of those problems under control but I did notice that after time, while running, the gauge read lower and lower yet the bowls remained full.

I would try adding a regulator ( http://store.summitracing.com/partdetail.asp?part=QFT-30-803&FROM=MG and did include a mounting bracket) and reset the float levels. This regulator is preset at 6.5 psi. 7 and over you risk overpowering the needle and seat. Don't waste time with the parts store regulators with the dial on them.
Click to expand...

I have the bouncy needle going on. I have no problem buying a regulator. My problem is I can't get the fuel pressure to stay the same..... it drops when the motro gets hot. Adding a regulator would not cure the problem I'm having will it? I mean the pressure drops to around 4 psi!

rumblefish360 said:
Theres a pair of good thoughts.
I'm with Moper on the fuel line. Odd routing. It did leave a question mark in my head as to why that way. OE runs the frame rail preety far up to the pump.
Heat in the carb was a wonderment in my head.
Click to expand...

So running the fuel line that close to the header is OK?? Are you really, really sure about that?? LOL! I'll go out here and look at it and see where it should be located down the rail. I didn't realize the OEM location was routing it that way.

I'm going take the carb off and look for trash in the bowls or anything that might be causing a drop in pressure.... actually I really don't know what I'm looking for. I've read that higher pressure will keep fuel from vopar locking. I don't know why but my pressure drops to 4 psi so then this allows the gas to vaporize and then I'm coasting down the road with the motor stalled. This has happen to me I know at least 4 times and each time I was lucky and coasted out of traffic.

Thanks for everyones help... keep those ideas flowing!
 
Took the carb apart ... nothing in the bowls and fuel lines.... I mean not one spec of foreign material.
 
The stock fuel line routing is along the frame rail to within (Approx.) 4 inchs of the fuel pump. Heat from the headers really isn't a problem there.
(And yea, a press. reg. won't help low press. only hi press. But you knew that.)
OH, good link C-spaz.

What kind of spacer is under the carb again?
Did you block off the heat crossover on the intake?
 
Sounds like a carb problem.What do you plugs look like,black,brown or white?
I would check your plugs to see what they look like first.Then I would check the float level.And I would check the needle and seat..
Jim
 
mullinax95,you said the small ,cheap electric pump that was on the car when you bought it,is only putting out 4psi.Why dont you replace that pump with one of better quality and more output then just regulate the pressure down ?
 
GOT IT!

I dropped the fuel line down to the frame rail and installed a 4" hose to the mechanical pump. I flipped the electric pump on and now have STEADY 8 psi at 200* with no pressure loss the whole time. Had the gas tank shut!

That was it.... I don't understand it but going up from the cowl then down the shock tower to the pump had something to do with it.

Now what to do about the to much pressure? Drive it and see what happens? Or go ahead and install a regulator?

THANKS EVERYONE!
 
17remfan said:
mullinax95,you said the small ,cheap electric pump that was on the car when you bought it,is only putting out 4psi.Why dont you replace that pump with one of better quality and more output then just regulate the pressure down ?
Click to expand...

Well now I've got 8 psi so all I really need is a regulator more than likely. Have you ever heard one of those pumps run? I tried all different types of mounting methods to try to quieten a Holley fuel pump and it never got where I liked it. I'm trying to avoid having to do that as much as possible. They are loud. The in tank fuel pumps are the ones to go for if you want quietness.
 
I would get rid of both the pumps and either get a good Holley electric or maybe a high volume Holley or Carter mechanical pump.
Jim
 
68383GTS said:
I would get rid of both the pumps and either get a good Holley electric or maybe a high volume Holley or Carter mechanical pump.
Jim
Click to expand...


I've already have a Carter pump now with less than 2500 miles on it. See the above pictures?
 
ok man here is what i would do before anything else/ pull the bowls off check the floats to make sure you don't have a hole in one of them easily done by submerging in water second looks like metering blocks on both the primary and secondary side of the carb which means power valves maybe one of them is busted if you are losing pressure there is a leak somewhere /check the ground underneath the car for fuel puddles if the diaphragm in the pump is bad there is only 2 places the fuel can go either on the ground or god forbid the inside of your engine if i can be of more help please post and i will help and research
 
sixpakmopar said:
ok man here is what i would do before anything else/ pull the bowls off check the floats to make sure you don't have a hole in one of them easily done by submerging in water second looks like metering blocks on both the primary and secondary side of the carb which means power valves maybe one of them is busted if you are losing pressure there is a leak somewhere /check the ground underneath the car for fuel puddles if the diaphragm in the pump is bad there is only 2 places the fuel can go either on the ground or god forbid the inside of your engine if i can be of more help please post and i will help and research
Click to expand...

LOL!

Thanks... but I got it fixed. Don't ask me why but it was the fuel line going up from the cowl and down to the pump (See pics). I moved the line to the frame rail therefore straight to the mech fuel pump. I was having a bouncy 7.5 psi and now it's a steady 8.

After thinking about this for a while now I bet the previous owner was having fuel problems because the way the fuel line was routed. At the time he had a stock mechanical fuel pump so he installed a electric fuel pump to help things out a bit. When I bought the car the electric pump's switch was on all of the time.
 
Sorry for not getting back to you after your PM but I was at work when I opened it and I was busy last night.

The routing of the fuel line, and the addition of the electric pump, was an interesting problem/solution on the previous owners part. I'm glad to see everyone step up and offer sound advice and you resolved it.

No go reward yourself by killing a tank of high-test... 8)
 
FASTBACK340 said:
Sorry for not getting back to you after your PM but I was at work when I opened it and I was busy last night.

The routing of the fuel line, and the addition of the electric pump, was an interesting problem/solution on the previous owners part. I'm glad to see everyone step up and offer sound advice and you resolved it.

No go reward yourself by killing a tank of high-test... 8)
Click to expand...


No biggie!

Yeah I would still be fighting with this. I didn't know the fuel line was supposed to be routed differently than the way I had it routed. Don't understand the why and how of it but all I know is my fuel pressure didn't drop but actually increased.
 
Good to hear you have this resolved. Moper was right about the fuel line routing as it would leave a bubble of air in the high spot which whould make the pump cavitate. Just like vapor lock, but not caused by heat. The previuos owner must have used the electric pump to try to overcome the problem.
 
Could it have something to do with gravity and the fuel being siphoned back to the tank working against the pump?
Andrew
 
A regulator wouldn't hurt, but an HP carb should be able to deal with 8 psi.

If you want to go electric, and want quiet. Try a Mallory pump. Way more reliable than the holley and *very* quiet too (not as quiet as a mechanical though-LOL). Vane vs. gerotor. The Aeromotive carb type pump is even louder than the holley.

Sometimes its the dumbest things. I had a fuel boiling issue when I got my car. it was because there was a small leak in the manifold by the flapper valve, which is right where the fuel line runs.

Glad you got it fixed.

Steve
 
You must log in or register to reply here.
-

Back
Top