Hi:- I have a 72 Vette small block which has been reworked 390hp. At the time of the installation I was going with a Holley fuel pump  but it wouldn't clear instead reinstalled the orginal pump. Running a Quadrajet 750 under load getting a ping had timing set both ways to sundown getting the idea that its staving for fuel . Looking at Edelbrock1721 will that work or do I also need the botten fuel plate kit 1798? Also concidering gm pump 6415325 the ones on the ZZ4 and the fast burn 385 will they clear? Last question these pumps have an inlet and an outlet the C3 Vettes have a fuel return line is that left open or plugged off does it have anything to do with fuel tank venting? I have the pvc valve going into the canister on the left side of the car which also goes back to the tank. Any advice would be appreciated. Thanks Garry

Hey Gary..I hear you on the pinging noise as I went thru the same thing..I guess before I would play with the pump what gas are you running..if you worked up the engine to a high HP what compression are you running? I went thru almost a 3 week test and tune with my car this summer and finally figured this is as good as it gets..well not so..I went to my small non chain gas station and got some ethanol free gas..that helped the ping a little..ok..went back to the same station and got the Cam 2 gas..yup 6,70 a gallon..car runs like a raped ape now! No ping and power out the ying yang..so my fuel budget is now..well I have no idea and don't care! Back to your car..have you done any fuel volume or pressure test yet? I looked into an Edelbrock fuel pump a while ago but don't need it..what type and heat range of a spark plug are you running? This can really be a big deal..other is are you running points? what type of coil do you have..or have you switched to HEI? Spark KV is something that can be changed real easy..also does the vacuum advance work at all?  what type of timing light are you using and does it show total advance and are you setting the initial timing with the vacuum advance plugged?  Are you sure you are on spark wire number one when setting the timing?  Just going to extreme basics here..I would play with fuel type and spark upgrades before fuel pump..the way my car is I probably have the original fuel pump on mine and have no fuel starving issue at all.. ok why do you have the PCV hooked up to the canister on the left side of the car??????I didn't know that the 72 had a charcoal canister??if so ok but it should be hooked up to the large vacuum port under the fuel inlet on the carb..if this is not a charcoal canister you hooked it up to the vacuum tank which would be interesting by itself.. yostusota2010-11-30 04:50:33

Hi Rich:- Good to hear from you I'll try to give the answers in the order of the questions. In Canada ethanol gas is the norm I'm running PetroCanada [Sunoco] 94. Edelbrock aluminum heads are used with the plugs recommended by them last year I had a tuneup done at my GM dealer by their Vette specialist and GM corresponding plug was installed also Msd 6al total ignition box, msd distributator and coil. The timing is back to 36 total advance at 3000. The reason I'm going towards the pump the orginal motor before rebuild was 200hp with probably a 650 Quadrajet, the pump was 70gal/hr at 7-8and a half lbs. Edelbrock is recommending 110 gal/hr at 6lbs. My engine with all the goodies matchs up to GM's fast burn 385 and the pump its running is 110 gal/hr at 7lbs. The car came out of Florida so it has the emissions control. The canister was used on 1970 - 1980 models. The shop that done the machineing and assembly included this Holley pump which was to large to fit a friend of mine to run this pump had to rework his frame. The ping is more noticeable in the hot weather. Garry   

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Adams' Apple2010-12-01 11:18:35

Well now that the engine is everything but stock changes everything..well I guess have you thought of going to an electric pump???  They have kits out there that will work very good for what you are doing..you are correct to rethink the pump choice as it may not have enough volume..as the recomended pump has lower pressure but bumps up the volume so it wont need a regulator..they are a nice setup..I am assuming you have an Edelbrock carb as well..ok the other thing I see here is MSD 6AL..wonderful!!  ok back to the plugs..what are you running and what gap are they and were they indexed??  This again is not a given deal..it must be tuned to the car..since you have a massive amount of spark the gap can and should be much larger..depending on plug type I have moved them out as far as 0.60..this will decrease your chances of detonation or lean misfire..have you put your car on a dyno yet.. a wide band O2 will pick up stuff that no ear or foot will ever do..does the MSD distributor have a vacuum advance??  ok and back to the pump ..you say that it is more noticable in hot weather..which makes me think you are running lean because the fuel might be to hot..which puts me back to an electric pump and some dyno time..to bad about the gas..there is only one station here that sells the 110 fuel and it is leaded!! I love the smell!! It makes me a little more happy than what I allready am..ok run this thru the mill..pull a plug and see if it glows or blows white..

Pinging is not caused by a bad fuel pump.  If you have retarded the timing a bunch and it still pings, it is probably running lean, but not from the pump volume.  Pump volume would work fine until it just ran out and lost power.  Pinging under load, if not timing, is almost certainly a jetting problem.  The best thing to do is get an air/fuel meter, lock out the secondaries, and drive it.  You should be reading about 12.6:1 under load and 17.6 at cruise.  Then activate the secondaries and do it again.  See which side is the problem and re-jet until it is fixed.

Larry

I'm wid Larry on this one. If it's pinging, it's gonna have something to do with the timing, or the quality of the fuel, not the quantity/volume. Tho, running it lean will make the combustion temps soar, which will make it ping due to the heat created, so then you may have a jetting issue. If the fuel pump was not providing the correct amount of fuel, it would be stumbling, like it was running out of fuel.
I haven't seen a mention of how hot/cool the engine runs, or what the true compression ratio is. Try a bottle/can of Octane Boost and see if it helps...I bet it will. IF it doesn't, its prolly time to bust out the carb tools, and do some jetting. Take a look at the sparkle plugs, and see what they tell you...that will give you a good idea of what might be causing the pinging.
Adams' Apple2010-12-01 11:28:09

Hi Joel:- Here's more info the carb has been built by Jet Performance you give them the engine the specs and they build you the carb it has the stage 2 kit. The vette is a toy it runs mainly highways usually running about 190 degrees. It has the Edelbrock rpm aluminum heads which will take about 1and a half to 2 degrees more timing at 40 and 38 total it likes 8base+25mech+3vacuumn of which an Accel adjustable vacuumn advance is used. Also Edelbrock hi volumne water pump ,the heads have no heat passages and the stinger hood is open at the windshield. My thinking is a stock fuel pump delivers 70gal/hr at 7and a half to 8 lbs is 38 yrs old feeding 750 cfm carb where the orginal was probably a 650. It probably is supplying enough fuel on the primaries but when the secondaries open it leans out. Everything has been tried so back to my questions so will the GM pump used on the ZZ4 work 7 lbs at 110gal/hr or Edelbrock 1721 or 1721 with bottem plate 1797 6lbs at 110gal/hr Edelbrock recommends. Finally how is the fuel retun line treated plugged or left open does it have anything to do with gas tank venting these 2 pumps only have an inlet and an outlet. 

You can plug the return line going back to the tank with no ill effects. If you do NOT plug it, you'll get fuel siphoning with a full tank. The tank venting system is either in the filler cap, or via the emissions canister on the driver side.

I can't help with the fuel pump selection, but...Stock fuel pumps were used on all Corvettes...even the ZL1, and L-88s, and those engines used waaaay more fuel(by volume) than even a hot small block. 

Joel is right on the volume on the stock pumps..By the way I love that hood!