A little background: Friend bought a pretty nice '67 L71 several years ago and shortly after the fuel pump failed, showing an external leak. He bought a replacement, supposedly correct AC Delco from the guy on the west coast who's usually the highest on all his stuff, paying over $400. Put it on the car and it wouldn't idle or hot start, so he sent it to a mechanic where he lived. He told me the mechanic was waiting for an adapter to check the fuel pressure, to which I said he's wasting his time and your money. So the test showed the pump was putting out 9 lbs. (so much for MY opinion). I bought a '66 L79 Nova a couple of years ago with similar scenario. New pump and car was miserable to drive. Shuts off at red lights, cranks all blubbery puffing smoke. So I put a gauge in the line and it's showing just below 9 lbs. I hated to put something non original on this car, but bought a Holley inline, NO return line regulator and plumbed it right into the side of the mechanical pump so it's not so noticeable, set it to 5.5 lbs and it made absolutely a new car out of it. It actually acts much better than even before the pump failed. I have multiple L71 cars of my own and have always thought they were ornery. Holley's in house shop has built one set of my carbs and a vendor that I've used for years has done others and the result is the same. My '67 that I drive more than the others has been especially bad lately, not wanting to idle and hard starting when hot. So I put a gauge on it tonight and it's showing 8.5 lbs. I believe that many of the people on the internet that are complaining of vapor lock and other similar issues as well as just simple tuning with flat spots, inconsistent idle speeds, etc are actually experiencing high fuel pressure which seems to be a major problem with not only no brand parts house pumps but also AC Delco replacements. I'm going to (RELUCTANTLY) butcher a fuel line on my '67 and put another inline regulator in it but there are obviously tons of correctly restored cars without regulators added and I'm wondering how many other people experience similar problems and how they're dealing with it. I do not believe that Holley carbs like anything above 6 lbs.
-
-
What guy on the west coast? Dont tell me i know. But he god around here.***************
late Oct 1969 L46 350/350, M21 4spd, 3.70 posi convertible --As with life, restoration is a journey, not a destination. Though restored cars provide both journeys AND destinations! -
Norris, what is the part number for the Holley inline, NO return line regulator you use with success.
Thanks FrankFrank Clark
U.S. Army Retired, current serving DoD Civilian
C1 1962 300hp, 4spd. Black/Fawn
C2 1966 Coupe, L79, A01, C60, J50, M21, N40. Silver/Black
C20 1966 Custom Camper, L30, J70, M49, N40, G60, Saddle/White
C20 1966 Custom Camper, L30, M49, N40, G60, Saddle/White
Comment
-
Yesterday I finally broke into the fuel line on my '67 L71 which as I've said has been ornery for years. It just has bad manners at idle, sometimes liking to cut off at a redlight and isn't real easy to re start at anything other than cold conditions. My '69 L89 has the same affliction. One set of the carbs was redone by Holley a while ago and the other by a vendor I've used exclusively since that I've had great luck with. So the gauge on the '67 shows 8.8 lbs. This car has an NOS AC fuel pump. Although I hate the thoughts of butchering a fuel line to mount a regulator down on the side of the pump I really don't see an alternative other than buying an aftermarket pump. As a side note one of my other cars is a '69 Camaro with a '70 LS7 crate engine. It has one of the larger appearing Holley chrome mechanical pumps on it feeding the 850 double pumper. I tested it also and it has 6.2 lbs and that car idles and runs flawlessly at low speeds. Grasping at straws here for alternative suggestions.Comment
-
Norris,
There is a 2009 posting by Joe Ciaravino who sounds very knowledgeable about carburetors and fuel pump pressure and he said Holley carbs like pressures of 5-7 psi. So, 8.2 or 8.8 psi sounds too high. Joe says on some fuel pumps the pressure can be reduced by the proper attention to internal adjustments during rebuilding, presuming the fuel pump is a rebuildable variety.
GaryComment
-
Frank Clark
U.S. Army Retired, current serving DoD Civilian
C1 1962 300hp, 4spd. Black/Fawn
C2 1966 Coupe, L79, A01, C60, J50, M21, N40. Silver/Black
C20 1966 Custom Camper, L30, J70, M49, N40, G60, Saddle/White
C20 1966 Custom Camper, L30, M49, N40, G60, Saddle/White
Comment
-
My 67 L71 factory fuel pump only had 5- 6 lb. fuel pressure and pass my PV drive test with no problem, anything over 6 to 9 lbs. needle /seat won't hold .Comment
-
Agree 100%. I've been testing many of my cars since I originally posted this, as well as various cars of friends and it amazes me how many of them have 7 to 9 lbs of fuel pressure, and how many just have bad manners, at idle, right off idle and when re starting. I've tested 5 so far with correct Delco pumps and so far have found ONE that was only slightly over 6 lbs with all the rest being higher. This seems to be an epidemic, and in my case reflects drivability issues that I've had for many years that I've written off as simply cars sitting around and not getting driven enough. The problem is that I don't know how to fix it without butchering original fuel lines to mount non bypass regulators that are noticeably incorrect and downright ugly to put it mildly. I can of course mount a regulator on the side of the pump on my '67 and '69 big block cars, but it's hard to butcher fuel lines on original engine/cosmetically correct L71 cars. My L88 has 7.5 lbs, but seems to tolerate it better than the tri power cars, or maybe it's just that we don't try to drive it the same way what little bit it's driven. As late as a year ago I thought people who were mentioning fuel pressure on seemingly stock fuel systems were howling at the moon, but have come to believe it's a major issue.Comment
-
Here is a screenshot of the fuel pressure specs for '67 from GM's Heritage kit:
You do not have permission to view this gallery.
This gallery has 1 photos.Comment
-
The specs for the Airtex reproduction of the 40083 pump are:
Minimum Free Flow Rate (gph) : 45 GPH @ 1800 RPM
Minimum Pressure Rate (psi) : 6.25
Maximum Pressure Rate (psi) : 7.5
GaryComment
-
Based on the stuff I've been fooling with lately and discussions with two different professional carb restorers I don't believe there's a Holley Carb in existence with center hung floats that will perform right with much over 6 lbs pressure. One of the carb guys made the comment that the side pivot, as in the single inlet like the 600's, have more leverage on the needles and will work with higher pressure. That having been said, my L79 Nova has been a royal PIA since I've owned it and regulating the fuel pressure to 5.5 has made a different car out of it. I'm going to be testing all three of my L79 Corvettes this week for comparison, but have already formed a strong opinion on the tri power cars.Comment
-
Norris,
FWIW, quite a few years ago I overhauled my 4657 pump for my 63 300hp car and reused the original diaphragm spring and even the inlet/outlet check valves. I deadheaded the pump out let line into my vacuum/pressure gauge and with the car idling the pressure was dead nut on 5 3/4 lbs. I agree with your feeling about the pump pressures on a carburetor car.Comment
-
Norris W. In several of your posts in this thread you mention your understandable reluctance to butcher or molest original fuel lines. Why not bend up a complete new line with the modifications from a store-bought length of 3/8" line? Leave your originals on the shelf, untouched.
I have a Holley on the 327 in my ski boat. It only gets used once a year, and I usually have carb issues off the trailer from it having sat dry for a year.
One issue I've had on several occasions is that the bowl floods while the engine is idling. The float level is too high, because there is liquid gas dribbling from the nozzles, and pours out of the sight plug. I screw the seat downward, but it won't 'stay' adjusted. At idle, it overflows again. The issue is the o-ring around the brass seat cartridge. (Not the needle and seat itself.) These either shrink, or deteriorate from ethanol fuel and thus fuel bypasses the seat and overflows the bowl. The engine runs fine off-idle where fuel being consumed exceeds the uncontrolled amount bypassing the cartridge. But at idle, the bowl level rises and you get the lousy idle and black smoke.
This condition will be corroborated by 'too-high' fuel pressure, may be mitigated by lowering the pressure, but it still exists. Easy to check if the carb has sight plugs on the sides of the bowls. (I don't know if OEM L79 carbs do or don't.) Let the engine idle. Remove the sight plug. If fuel is dribbling out, raise the engine speed and watch the level in the bowl. If the level recedes at off-idle, return it to idle. If the level again rises and dribbles out, the seat o-ring is bypassing.Comment
Comment