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Old 04-29-2002, 05:59 PM
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Post fuel pressure question for a 350 SBC

I am having trouble with a rich mixture at idle as described in my earlier post. My engine has basically a stock cam in it and I'm sure it's not in need of a HV pump. I Emailed Edelbrock and they advised me that I should have no more than 6 psi fuel pressure. I have a Holley High Volume mechanical pump that claims 80 gph and a 7.5 psi shutoff pressure. What's your thoughts, would this pump just push the fuel through the needle valve and cause a rich condition? Almost every pump that I see in the mags puts out more than 6 psi. None of the few that I see that push 6 psi are chrome....gotta have chrome!

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Old 04-29-2002, 06:11 PM
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One of those low buck Carter electric pumps put out 5-6 psi but they are not chrome, you could use a regulator but they will cost nearly the same as a fuel pump. How about putting a factory style mechanical pump back on, you can get chrome ones from most suppliers like Summit or Jegs etc. Are you sure it's not your needle and seat or float settings?
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Old 04-29-2002, 06:11 PM
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small block chevys call for 5 to 7 psi if the pump pushes more it could cause rich condition if you want to use the hi pressure pump get a fuel pressure regulator they come in chrome also and you will be able to reduce the pressure and rich condition
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Old 04-29-2002, 06:27 PM
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4 Jaw...I did not check my float yet, but that's next. I did look in Jeggs and did not find a stocker that was chrome. I like the fact that the Holley can be rotated 360 degrees but I guess it doesn't really matter if it's not working right. I have been planning to change my pump anyway because of the fuel seepage that I was getting around the screws. The thing only has 3400 miles on it but there is something wrong with it. I removed the lower screws and put teflon paste on the screws because the fuel was seeping out around the heads of the screws. I didn't really go much further yet..keep the advice coming!
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Old 04-29-2002, 06:58 PM
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Edlebrock has a chrome mechanical fuel pump that puts out 6 psi, that is what I am using with my Edlebrock Performer carb. I don't remember if I got it from Jegs Or Summit. I was using an electric pump but it over rode my needle and seat and flooded.
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Old 05-05-2002, 11:23 PM
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Yes, too high a fuel pressure WILL cause a too rich condition, and your fuel pump is probably the problem. Putting a too-high pressure fuel pump on and then using a regulator to step the pressure back down is (excuse me) a kinda s-----d thing to do, by the very nature of the thing.It is like standing on a ladder, and complaining about the height.(!) By the way, I suggest you leave the floats alone, most people screw up their carbs trying to "adjust" the float. Why would your floats be off? By the way, be careful using teflon or silicone around carbs, they tend to be soluble in gas and cause a thousand more problems than they cure! NEVER use either in your fuel inlet threads, or you can probably kiss your carb goodbye. Oh, and if the fuel pump really isn't causing the too rich condition, then your carb probably has "dirt" (read: contamination of some kind, like rust, or gum or varnish) in it. This is USUALLY the cause of the typical too-rich condtion. Many a rodder has bought himself a trip to his local carburetor shop because he thought the floats needed adjustment, and tried to do it himself, instead of dealing with the contaminants in his fuel. And no, spraying carb cleaner down the throat of the carb won't do a darned thing to fix the problem, either. Somettimes a quick fix for a dirt-caused problem is to put some gasoline stabilizer in your tank, and run the engine to be sure it gets into the carb float bowl. Sometimes this fixes it, sometimes not. If all else fails, change gas stations for a while. Some gasolines have a stickness to them that makes the needle in the needle and seat stick open or shut on particular carbs while not bothering other carbs.
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Old 05-06-2002, 08:01 AM
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if your engine is mostly stock,(aftermarket intakes don't matter) you don't need a huge fuel pump. you also don't need a huge carburetor on a stock on stock cammer engine. what i would do is calculate the volumetric efficiency of the engine as close as possible, and then rejet the carburetor to it. then you have options. you can use a regulator, but that takes up space. you can buy an adjustable flow holley or edelbrock pump possibly through jeg's or summit, but i would go direct to holley or edelbrock for a custom job. even on a hot engine you should run no more than 8 psi at any given time. good luck!
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Old 05-07-2002, 04:25 PM
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Has anybody asked what kind of Carb he has on the engine??? If he has a Holley Carb on it and the engine back fired back through the carb at any time it just blew the power valve. Food for thought.
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Old 05-07-2002, 07:01 PM
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I agree with Lloyd, a blown power valve will give you rich idle and behave like about 5jet sizes too big. I think if you were having fuel pressure probs, you would have trouble controlling needle and seat and would have flooding.

Hope this helps.
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Old 05-07-2002, 08:27 PM
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lloyd and rick is right on target carb.carb. carb. Ive been a round the block a few times. Ive ran all types of fuel pumps never had a problem with fuel pressure problems.of course ive only ran holleys anything else is a creature to me.you cant expect to pull a carb. out of the box with out making some adjustments for your criteria no motor is the same.(wrenchturner)
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Old 05-07-2002, 09:30 PM
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Hi, Scumdog from New Zealand here, I had a similar problem that plagued me for years - I tried new needle and seats, swapped carby bodies, put in new power valve and still I had a problem of the engine running O.K. when I tuned or replaced one of the above items but then over a few months (or less) I would have a mixture that was too rich.
Sometimes when it was running rich I found that disconnecting the electric fuel pump caused the engine to smooth out and the mixture was O.K. but I guessed I couldn't drive like that!
The problem was simple - I had a microscopic hole in the brass float at the primary end of my 780 Holley, as the fuel got warm from running the engine the air inside the float would expand and (I guess) let out a stream of tiny bubbles, when the engine cooled off the air in the float would contract and the resulting vacuum would suck in fual and the float would sink a small amount. After a few cycles of that the float would be low enough to richen the mixture - I would have a "fiddle" and the problem would go away for a while and then start again.
Sorry for being so long winded but I thought I would fully explain the situation, Cheers, Scumdog
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Old 05-08-2002, 11:35 AM
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The fuel pump would be my last guess. Check you carb. It sounds like you have a Edelbrook, If it's a Holley thatís a common problem. Get a good carb guy to take a look. If your loading up, you may have a leak in your carb. Thatís bad because it can cause damage to you cylinders
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Old 05-09-2002, 08:02 AM
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aftermarket fuel pumps are precise. you need to have them right. edelbrock's don't have power valves so if your'e running one forget that part. if it's a float i'd be surprised because it would be running fuel constantly and would die all the time. i have seen this problem with fuel pumps being the kicker so many times it's not even funny. go to the parts store, buy a cheap stock pump (like 15 dollars) and put it on. if it doesen't help, take it back and get a refund. if it still runs ritch and it's a 'brock, it needs re-jetted. you can check the float, but iv'e never ever in ten years of running edelbrocks had a float go to hell. 9 out of ten times it's the fuel pump. the other one out of ten it's the jetting.
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Old 05-10-2002, 07:58 AM
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I'VE HAD THE SAME FUEL PUMP ON MY 600 HOLLEY FOR LIKE THE LAST 5 YEARS WITH NARY A PROBLEM. HOW IN THE HELL IS 1.5 PSI GOING TO MAKE ANY DIFFERENCE? GIMME A BREAK, YOU GOT CARB PROBLEMS. I CAN TELL CAUSE ME WEEGEE BOARD SAID SO.
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Old 05-10-2002, 06:28 PM
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hi bean here from pa has any one thought of ignition problems in some rare cases ive seen problems in the dis cause the carbe to act funny also check your pcv valve poor ventalation can cause a problem. but if you do have a holley then you defenatly have a blown power valve


bean
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