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Is it possible to drain a carb dry under acceleration?

hangn0ut said:
A round back alternator with electronic ignition can give you problems...just saying.
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I feel like the RCA Victor dog after that one. :wtf:
I have the usual dual field alternator that charges like a mofo?
 
hangn0ut said:
Here,try this. Drive normally up to about 70 mph or so. Now downshift and punch it. Now you should be able to go well past that point where it stumbles if it is a fuel problem as you are at full throttle for a much shorter period of time.
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See, that's the thing. In 1st and 2nd full boogy, floored until redline, it doesn't run out of steam or falter at all. Once into 3rd (or sometimes it waits until 4th even), up over 4000RPM, all of a sudden uggggg, out of gas.
Lift, let it catch it's breath, a couple seconds later it's ok.

Hey, I just thought of something else here.
I drive the car once a week or so and every time, it has lost its' prime (bowls are dry?) and it takes several cranks to get any fuel back up to the carb.
Wonder if that is of any importance here?
 
moparedtn said:
See, that's the thing. In 1st and 2nd full boogy, floored until redline, it doesn't run out of steam or falter at all. Once into 3rd (or sometimes it waits until 4th even), up over 4000RPM, all of a sudden uggggg, out of gas.
Lift, let it catch it's breath, a couple seconds later it's ok.

Hey, I just thought of something else here.
I drive the car once a week or so and every time, it has lost its' prime (bowls are dry?) and it takes several cranks to get any fuel back up to the carb.
Wonder if that is of any importance here?
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You missed what I'am getting at. Try what I suggested and it still looses power as before what then?
 
gauge on. Check at idle, should be 4-6 at least. Measure pump pushrod length and check if diaphragm is leaking. My last Carter pump died with weak pressure and then flooded the crankcase with fuel when the diaphragm failed. At wot the pressure should stay above zero or the bowls will drain dry. This has happened to me.

bowls draining after sitting is "normal" with these carbs. Haven't figured out if its boiling out or draining out. I drive daily this summer and mine starts right up on same day starts but two days or more takes some cranking.
 
"bowls draining after sitting is "normal" with these carbs. Haven't figured out if its boiling out or draining out. I drive daily this summer and mine starts right up on same day starts but two days or more takes some cranking."

It's not just these carburetors. It's ALL carburetors because they vent to the atmosphere and today's gas evaporates quickly compared to years past. As he said, if you drive the car every day or even every other day, you won't have the long cranking times. As for the question about "can anything in the carburetor be the restriction", based on 50 years of tuning, see my prior post #15 and Doug's post. As was stated, if you cruise along at 65-70 mph and then punch it, see how it responds...
 
Roger all this. Reckon I'll fashion some sort of remote gauge setup and experiment as advised and see how things go, then report back.

I seriously doubt the pump diaphragm has failed; I do as habit pull the dipstick and check for fuel quite often out of paranoia. :)
Also as already stated, pushrod is new.

Let me figure out how to rig up a gauge I can see from the cockpit and I'll report back. Heck, I might even make a video or something. :)
 
Well forget that noise.
I had no idea what an electric fuel pressure gauge cost....

Now I do.:realcrazy:
So much for that idea.
No, I'm not interested in running fuel into my cockpit for a mechanical gauge.
 
Temporarily zip tie a mechanical gauge to your cowl area or windshield wiper just for testing purposes. Yes, you would NEVER run fuel into the cabin.
 
coloradodave said:
Temporarily zip tie a mechanical gauge to your cowl area or windshield wiper just for testing purposes. Yes, you would NEVER run fuel into the cabin.
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I have an 1/8" NPT outlet on my fuel line now that I just bought a little mechanical gauge for. Would it be accurate enough to simply take some "rubber" fuel line from that port and extend the gauge up to where I could see it thru my windshield?
 
What was the ambient temperature at the time? Was there extended idling just prior to the romp. I think I ran my 850 Demon dry one time just goofing around and gunning it after extended idling in hot conditions. Has not happened since. Did you duplicate the scenario to see if it does it again.
 
Dennis H said:
What was the ambient temperature at the time? Was there extended idling just prior to the romp. I think I ran my 850 Demon dry one time just goofing around and gunning it after extended idling in hot conditions. Has not happened since. Did you duplicate the scenario to see if it does it again.
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About 90F or so. Engine hangs at about 180F at that temperature typically, although it will climb to just shy of 190F while going down the highway at a steady 60+MPH (3.55 gears).
Naw, about a mile of in-town leading up to the highway romp in this case.
This rascal has a bit of a history with high RPM-higher gear "nosing over" at times, even with a different carb (Holley 750).

Other times, not so much:

I short-shifted into 4th in the video, about 5000RPM or so. No nosing over, just that one momentary hiccup in 2nd.

In my most recent romp, I was really stretching her legs some, running it up past that pretty hard in all gears. She nosed over in 3rd at over 4000RPM or so, then recovered once I lifted.
 
It occurs to me that the common item in all these trevails of the engine starving out (if that is, indeed, what is happening here) is the repro sending unit/pickup.
It's 3/8", but what if there's an issue with the sock or the way it's oriented in the tank or some such?
Pondering...
 
Well, the good news is it has around 7psi fuel pressure at idle and that drops to around 5psi when I hammer it, so I reckon that's acceptable.

More good news is that I installed an electric oil pressure gauge successfully and relocated my temperature gauge beside of it.

Bad news is...according to this Bosch (yes, it's a cheap one) oil pressure gauge, well, she ain't got much. 25psi @ idle, revs to 35psi. Gets a little worse as she gets hotter, of course.
Damn. I can't afford an engine at this point, but this one apparently ain't got long to live.:(
 
I trust a cheap mechanical guage way more than cheap electric one. Teflon tape on the sender might mess up an electric guage.
 
hangn0ut said:
I trust a cheap mechanical guage way more than cheap electric one. Teflon tape on the sender might mess up an electric guage.
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I've read folks post that about teflon before, but when using Teflon tape on threads (which is what I do with any piping, since I'm a 35+ year fire sprinkler guy by trade) there is still plenty of metal on metal going on there.
To me, the "circuit" either has a good ground or it doesn't. If the gauge works, then it's got a good ground, right?

I've also read that a new sending unit needs to break in, that the spring in those are pretty stiff when new, but maybe I'm just grasping at straws there.
The gauge does act really stiff....
I suppose I need to try a different gauge as confirmation of what this one is telling me also.
I've veered off the topic of this thread with all this. I need to start a new one.
 
UPDATE: 9/21/16.
I am reviving this thread. :)

Now that I've replaced the entire top end of my engine... (see my thread: http://www.forbbodiesonly.com/mopar...lls-a-fresh-set-of-906s-on-the-ol-440.117561/ )...

I've taken the car out a couple times since the rebuild and she really runs great. Very smooth. I'm tickled. :)
However, today I decided it was time to beat on her a little bit, so I hit the 4-lane and started wringing her out.
First gear was great, so into 2nd and hammered it again. She pulled great all the way to 5000rpm and then - she fell flat on her face.
She ran out of gas for a moment!
Didn't die, just flat laid down.
I lifted, shifted up to 3rd and waited a couple moments, then resumed a little throttle. She picked right back up and ran uneventfully the rest of the way home.

Now, when I first started it up after all that work, the fuel gauge showed the usual 6.5psi idling.
When I got home today and looked, it only shows about 4-4.5 psi. ;-(
She runs fine normally and even with a little light romping, but when you get serious, she literally goes dry.

Reminder - entire fuel system is new, from gas tank to sending unit to fuel lines to Carter "hemi" fuel pump to Edelbrock AVS. Even the fuel pump pushrod has been replaced.
Float levels in carb have been checked and re-checked.
Gas cap is vented, even though the tank retains its' factory vent lines as well.

What the heck is going on? I can accept that the carb is undersized (650cfm) but that doesn't explain what is happening here.
She is flat running out of gas when in hammer mode.
Is it possible the sending unit is collapsing under hard suction?
 
My car was doing the exact same thing, it would only do it if I was hard on the gas for long pulls. I had been running the same exact fuel delivery system reliably for 2 years so plumbing size and sending unit issues were out, checked all lines then strapped a fuel pressure gauge to the hood and bingo. 7 psi at idle then a sustained 5 psi but keep pushing threw the gears and running the rpm's up and it noses over as the gauge nearly zero's out..... not enough volume. Pitched the imported Holley, bought a Carter, drilled and tapped out the ports from 1/4" to 3/8" NPT to be less restrictive, no more problems.
 
747mopar said:
My car was doing the exact same thing, it would only do it if I was hard on the gas for long pulls. I had been running the same exact fuel delivery system reliably for 2 years so plumbing size and sending unit issues were out, checked all lines then strapped a fuel pressure gauge to the hood and bingo. 7 psi at idle then a sustained 5 psi but keep pushing threw the gears and running the rpm's up and it noses over as the gauge nearly zero's out..... not enough volume. Pitched the imported Holley, bought a Carter, drilled and tapped out the ports from 1/4" to 3/8" NPT to be less restrictive, no more problems.
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You know, you bring up a point I've wondered about myself since I installed the Carter "hemi" fuel pump that Mancini sells:
http://www.manciniracing.com/cabheen5psis.html
I always wondered why the inlet and outlet on these is only 1/4" NPT.

For example, the Edelbrock pump (that looks just like the old Carter design) has 3/8" NPT inlet and outlet, yet is rated for 10gph less than the Carter is?
http://www.manciniracing.com/edmeperpmse6.html

I do have an almost new "regular" fuel pump sitting on the shelf I could try, but its' inlet and outlet sizes aren't so great, either - and it's not rated nearly as high on flow rate.

As an aside, this thing seems to drain the fuel bowls in the carb after just sitting a day or two also. Wonder if that's from evaporation or the pumps' check valve
not holding?
Could it be related?
 
Really hard to say from all the info given BUT!, what size is your Fuel Line (if stock? TOO Small), Sending Unit, Stock ? TOO Small!! what is the GPM on the Pump???

FYI i run All 7/16 Lines, AKA -8,
Better up grade ! running Lean could Toast your Motor !!
Ill post pics
 
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