fuel pressure
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Racer
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Mine is running 2 psi though fuel flow is good. I cant find the actual specs in my shop manual or on line. The external fuel filter has that return line which I wondered if it effected the actual PSI #s. I have read that Q jets dont like anything over 5 psi. Some suggest a pressure regulator. Having bogging issues and erratic idle speeds. thought this low PSI reading might be the culprit though I have also read fuel flow is more important than fuel pressure. Some suggest a pressure regulator.
Last edited by greggome; Sep 1, 2018 at 10:28 PM.
Is my vette stock?? HAHA
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edelbrock is about 4 psi. Quadrajet is 5-7. I have a carter mechanical fuel pump that puts out 8psi and I regulate it down to 6. Runs good and strong. Easy starts once its been started from 4 or 5 hour shutdown.
327, stock bore, 10.5:1, sportsman 2 heads, 64cc chamber, comp cams .488/ 236 duration. 365HP, quadrajet carb rebuild by Lars, RPM intake, 1 inch phenolic spacer, ramshorn 2.5 to 2.5 sweet thunder pipes
327, stock bore, 10.5:1, sportsman 2 heads, 64cc chamber, comp cams .488/ 236 duration. 365HP, quadrajet carb rebuild by Lars, RPM intake, 1 inch phenolic spacer, ramshorn 2.5 to 2.5 sweet thunder pipes
Thread Starter
Racer
Joined: May 2009
Posts: 316
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edelbrock is about 4 psi. Quadrajet is 5-7. I have a carter mechanical fuel pump that puts out 8psi and I regulate it down to 6. Runs good and strong. Easy starts once its been started from 4 or 5 hour shutdown.
327, stock bore, 10.5:1, sportsman 2 heads, 64cc chamber, comp cams .488/ 236 duration. 365HP, quadrajet carb rebuild by Lars, RPM intake, 1 inch phenolic spacer, ramshorn 2.5 to 2.5 sweet thunder pipes
327, stock bore, 10.5:1, sportsman 2 heads, 64cc chamber, comp cams .488/ 236 duration. 365HP, quadrajet carb rebuild by Lars, RPM intake, 1 inch phenolic spacer, ramshorn 2.5 to 2.5 sweet thunder pipes
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
the regulator just maintains a set available pressure. If you are only getting 2 psi from your pump, you will need a new pump. I dont know why your pump pressure is so low but my new from summit Carter pump broke after a couple of hundred miles and they sent me a free replacement thats been going strong for atleast 500 miles now. My broken pump was putting out 2-3 psi.
I have the stock A/C fuel filter with the return line and I can get 6 psi no problem. I think the return line is small enough that it just deals with back pressure
I have the stock A/C fuel filter with the return line and I can get 6 psi no problem. I think the return line is small enough that it just deals with back pressure
Last edited by Rescue Rogers; Sep 2, 2018 at 07:59 AM.
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From: At my Bar drinking and wrenching in Lafayette Colorado
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From: At my Bar drinking and wrenching in Lafayette Colorado
It won't cause a hunting idle.- 2 psi is enough to produce stable idle and normal cruise performance. It will cause the car to lean out and "fall on its face" at the top end of 1st or 2nd gear at wide open throttle.
Lars
Lars
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Jebby
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Racer
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My first thought was a vacuum leak. I have checked and rechecked vacuum readings at the manifold they run low at 8 but are steady with no fluctuation or flutter. Have hunted leaks using propane, smoke and carb cleaner with no success. Just completed compression testing all is good.
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Put a timing light on it and see if the timing changes corresponding to the "hunting." Timing should be rock steady. If timing is fluctuating, it will cause a change in idle speed and idle quality. The fact that you've had 2 different carbs produce the same results indicates that it's not a fuel system problem.
Lars
Lars
Last edited by lars; Sep 2, 2018 at 01:21 PM.
Dr. Detroit
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Racer
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Hard to get RPMs to sit steady at stock 750 RPM but it maintains a fairly steady idle at around 600 RPM allowing me to get a better look at the timing mark. With this steady idle speed there is no bounce or jumping of the timing mark. As I increase the RPMs and watch the timing mark as it moves up and hold it at different RPM levels I dont see any bounce either.
Dr. Detroit
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From: New Braunfels Texas
Hard to get RPMs to sit steady at stock 750 RPM but it maintains a fairly steady idle at around 600 RPM allowing me to get a better look at the timing mark. With this steady idle speed there is no bounce or jumping of the timing mark. As I increase the RPMs and watch the timing mark as it moves up and hold it at different RPM levels I dont see any bounce either.
Jebby
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From: At my Bar drinking and wrenching in Lafayette Colorado
And to do that, disconnect every single vacuum line on your carb and plug every port on the carb. That includes the power brake line/fitting, PCV, vacuum advance, and every single other line and port on the carb. Disconnect and plug. Then see if the idle quality changes.
Lars
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
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From: New Braunfels Texas
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,026
From: New Braunfels Texas
And to do that, disconnect every single vacuum line on your carb and plug every port on the carb. That includes the power brake line/fitting, PCV, vacuum advance, and every single other line and port on the carb. Disconnect and plug. Then see if the idle quality changes.
Lars
My 72’ Changes idle when you activate the headlights and wiper door!
Jebby