Question on loosing fuel pressure going down track.

Jeff Stout · 01-22-2020, 07:45 PM

Quote:

Originally Posted by MRE 7171

Jeff did you get a chance to check the volume in a fuel jug for 60 seconds at the front of the car and what volume did you get?

I just did now im right at a gallon in 60 seconds. That was tested using line right at carburetor

gsa612 · 01-22-2020, 08:12 PM

Quote:

Originally Posted by Jeff Stout

I just did now im right at a gallon in 60 seconds. That was tested using line right at carburetor

On a free flow test it should be a gal.in 30 seconds especially with a Q-jet...gsa612

Danny Ashley · 01-22-2020, 08:14 PM

Should pump a gallon in 30 seconds. I think you just found your problem.

Mark Yacavone · 01-22-2020, 09:25 PM

Quote:

Originally Posted by Danny Ashley

Should pump a gallon in 30 seconds. I think you just found your problem.

Agree..I've had cars under 25 sec.

BTW, I was just giving Jeff a hard time. Sorry some of you missed this whole sordid tale, for 5 years ...Check out the build section once in a while ;-)

ss3011 · 01-22-2020, 08:25 PM

Its weird that the O2 sensor goes rich , sounds like some work needs to be done to straighten out the fueling of the carb . That being said the carb is using more fuel than can be supplied to it , so the pressure drops . My recommendation is to figure out what's up with the carburetor , but also make sure your fuel system is up to the task . My Q-jet is fed from a BG400 pump through a dash 10 line , and stays right at 6.5 psi throughout the run . Dyno pulls show the A/F ratio varies from 12.8 at 5000rpm to 12.4 at 7400 rpm .

Jeff Stout · 01-23-2020, 10:42 AM

Quote:

Originally Posted by ss3011

Its weird that the O2 sensor goes rich , sounds like some work needs to be done to straighten out the fueling of the carb . That being said the carb is using more fuel than can be supplied to it , so the pressure drops . My recommendation is to figure out what's up with the carburetor , but also make sure your fuel system is up to the task . My Q-jet is fed from a BG400 pump through a dash 10 line , and stays right at 6.5 psi throughout the run . Dyno pulls show the A/F ratio varies from 12.8 at 5000rpm to 12.4 at 7400 rpm .

This seems to be what I'm struggling with. I make small changes to jet,rod,hanger and have not found sweet spot. In the beginning I was way over rich and way over revving on gear change and car went faster. Would think car would pick up allot if afr was correct in 3rd gear

Dave Gantz · 01-23-2020, 12:18 PM

Did you do the volume test with the engine running? It'll pump more, of course, when the voltage regulator is holding it at 14.7v or whatever it maxes out at.
As mentioned, are your grounds, connections and wire diameter up to snuff?

Jeff Stout · 01-23-2020, 12:40 PM

Quote:

Originally Posted by Dave Gantz

Did you do the volume test with the engine running? It'll pump more, of course, when the voltage regulator is holding it at 14.7v or whatever it maxes out at.
As mentioned, are your grounds, connections and wire diameter up to snuff?

Going to verify ground as car was a back east car and frame had some rust. Maybe move ground to rear battery.

ss3011 · 01-23-2020, 01:45 PM

Everyone is focusing on a fuel pump delivery problem , yet the engine goes rich in high gear . That seems to be the real problem .

Bob Mulry · 01-23-2020, 02:30 PM

Quote:

Originally Posted by ss3011

Everyone is focusing on a fuel pump delivery problem , yet the engine goes rich in high gear . That seems to be the real problem .

Just my 2 cents.....

A lean miss will do that....

01-22-2020, 08:14 PM	#3
Danny Ashley Member Join Date: Nov 2001 Location: Marion,In. Posts: 267 Likes: 60 Liked 110 Times in 29 Posts	Re: Question on loosing fuel pressure going down track. Should pump a gallon in 30 seconds. I think you just found your problem.

01-22-2020, 08:25 PM	#5
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Question on loosing fuel pressure going down track. Its weird that the O2 sensor goes rich , sounds like some work needs to be done to straighten out the fueling of the carb . That being said the carb is using more fuel than can be supplied to it , so the pressure drops . My recommendation is to figure out what's up with the carburetor , but also make sure your fuel system is up to the task . My Q-jet is fed from a BG400 pump through a dash 10 line , and stays right at 6.5 psi throughout the run . Dyno pulls show the A/F ratio varies from 12.8 at 5000rpm to 12.4 at 7400 rpm .

01-23-2020, 12:18 PM	#7
Dave Gantz Senior Member Join Date: Nov 2005 Location: Verrry South Jersey Posts: 537 Likes: 134 Liked 251 Times in 125 Posts	Re: Question on loosing fuel pressure going down track. Did you do the volume test with the engine running? It'll pump more, of course, when the voltage regulator is holding it at 14.7v or whatever it maxes out at. As mentioned, are your grounds, connections and wire diameter up to snuff?

01-23-2020, 01:45 PM	#9
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Question on loosing fuel pressure going down track. Everyone is focusing on a fuel pump delivery problem , yet the engine goes rich in high gear . That seems to be the real problem .