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  #16 (permalink)  
Old 07-21-2004, 04:34 PM
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Technically that motor shouldn't evan NEED a 4bbl as they come w/ 295cfm 2bbls.
But a 600 vac sec doesn't seem rediculous to me on a stock 307.No worse than having a 750Q-jet on a stock 350.We had a 600 holley on a 305 w/ a very mild cam(K-1102 summit)and headers and it worked very well for performance and the mixture was fine.
If your having a rich problem its prolly something in the jetting or metering.
Also as far as secondarie springs if you feel a sudden burst of power your springs are to heavy.Go lighter on spring size one at a time till the car actually has a slight bog when you punch it,then go one size backward.

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Last edited by 78 monte; 07-21-2004 at 04:45 PM.
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  #17 (permalink)  
Old 07-21-2004, 04:47 PM
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78 Monte, the differance with the 750 cfm Qjet is its spread bore design. itll work great on everything from V6s to 500 CI Cadillacs.
It would be a differant ball game with a square flange carb.
If it were my 307, Id use a 500. 500 is enough carb for a 307to 5000 RPMs easily, & since its a stock 307 itll never see past 4500 RPMS anyway.
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Old 07-21-2004, 08:12 PM
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After a whole mess of google searching, I found this:
http://www.edelbrock.com/automotive/eps_sect2.html

The whole manual is here:
http://www.edelbrock.com/automotive/eps_intro.html

I haven't had a chance to read it, but I'd bet that if the problem is your carb, there's enough information there to solve it.

Actaully, if you read this page first you'll gain a pretty good understanding of how your carb works.
http://www.edelbrock.com/automotive/eps_sect1.html

Last edited by Terje; 07-21-2004 at 10:21 PM.
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  #19 (permalink)  
Old 07-21-2004, 11:09 PM
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500 or 600 cfm

instead of wasting the money on another carb. if you already have a good carb. why done you simply install a regulator and gage.then you will not only know what your press. is all the time(after a little trial and error to find the satisfactory operating press)but you'll have a nice looking set up to.shouldn't cost for than $50-$75.00.then you can spend the rest of your money on a new cam or a pair of slicks or something.
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Old 07-22-2004, 07:00 AM
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Terje, That looks just like mine except I have the manual choke version.

I have the Edelbrock manual and I was going to buy the calibration kit until several people told me the 600 cfm carb is too much carb. I have re-read all the discussion in this post several times and I am beginning to think I can meter my present carb down and it will work fine. I have studied the manual extensively and I have checked all the setting recommendations. The last step is to do the metering. I think I will start there first with the hope of saving some $.

I have a fuel pressure regulator installed and it is set at 4.5 lbs. I'm going to dial it down to 4 lbs. to see if it makes any differance.

I realize this is to a certain extent a trial and error process, and it would not be a problem if I had a box full of various parts to work with, but I don't. So every time I make an attempt to correct the problem I have to buy new parts, and if it does not work, I'm stuck with more useless parts and my problem.
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Old 07-22-2004, 07:15 AM
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Changing to a 500 from a 600 won't make the motor run a bit different........The 500, 600, and 625 AFB style carbs all have the same 1 3/16" primary venturi. Throttle response, fuel mileage, air speed, and Primary jets/ rods will be the same on all three carbs. Just because they are a square flange carb doesn't mean all four holes are the same size. The AFB/Edelbrock carbs have vacuum operated secondaries. The motor has to flow enough air threw the front bores to max them out before the back half even opens. Then it only opens as far as the motor will take.

Get one of Edelbrocks tune-up kits for your carb. It will have the jets, metering rods, and springs needed to get a proper tune on the carb you already have. It comes with a good book that has an easy to read chart that will let you make changes in your fuel curve. I little trial and error will have you dialed in in no time. Dan
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Old 07-22-2004, 07:34 AM
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i ran a EDelbrock 750cfm on my 305, and it ran better with the 750 than with the 500cfm
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Old 07-22-2004, 11:00 AM
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Yes, that is what my carb looks like except mine has a manual choke.

I have ordered a rod & jet set from my local Ramchargers store. I'm goingto go the $52 route instead of the $280 route to replace the carb. I agree with Terje that the engine can only gulp so much air and excessive cfm of the carb makes no difference. The part I'm not convinced of is that the internal fuel passages that are drilled into the body of the carb cannot be changed and if they are over sized, then rejetting the carb will not improve the F/A ratio. I hope to disprove my own theory by rejetting the thing.
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Old 07-22-2004, 12:50 PM
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Another thing I was thinking you might want to try.

You said that the thing barely idles and idles real crappy.

You might want to try making it idle, then drop a little gas down the carb and see if the engine dies or speeds up. (maybe a tablespoon or so)

Maybe also try cutting off the gas supply to the carb. See what happens as it's about to run out of gas. Does it speed up and run better before the engine dies or not.

I wish I had thought about this before.

The thing is, I'm not 100% confident that the problem is your carb at all. It could be your ignition system.

You need compression, air, gas, and spark for it to run. Check each of those things to make sure it's getting them all in the right proportions and timing.

You've already checked for vacuum leaks, but who knows, there might just be a hard to find leak somewhere.

My truck had a crack in the PCV valve that I didn't notice. I do know that when it's idling, and I remove the hose from the PCV valve it runs real crappy, then dies. The crack didn't kill the engine, but I'm sure it effected the idle performance.

A vacuum leak problem might be fixed by adjusting the carb to output more fuel, and your engine might run fine, but the vacuum leak is likely to change over time making your engine seem very unreliable.

Also, when you attempt to adjust the idle mixture, are you completely tightening down the screws? or unscrewing them all the way to make it run? I'm wondering if your engine is in need of more fuel or less.

How old are your plugs, wires, cap and rotor? Is your timing correct?
Every time I've had problems with the ignition, it's been under load and not at idle that I've had the problems, but who knows.

Last edited by Terje; 07-22-2004 at 01:01 PM.
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Old 07-22-2004, 01:00 PM
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I just replaced the whole ignition system going from points to hei. I regapped the plugs to .045. New wiring and fuel filter too. It made some improvement. I will replace the pvc valve. And I will try the experiments cutting off the gas and dripping gas down the throat to see what it does.

Because the car does not restart quickly after it is warmed up, I tend to think it is flooding. I'm also going to reduce the fuel pressure to 4.0 and 3.5 lbs to see if that makes any differance.
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Old 07-22-2004, 01:07 PM
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Already at 4.0 psi you're below the 6.0 psi recommended in the manual. I'm guessing that above 6.0 psi maximum that carb's float is unable to shut off the flow to the float bowl, and so it'll flood your engine. Anywhere 6.0 and lower should not have this problem.

There should be a lower limit where the fuel pump can't get enough fuel into the bowl, but you shouldn't see signs of this at idle, or you wouldn't even be able to drive this thing.

It doesn't cost anything to try, so it's worth a shot.

There is a possibility that the needle activated by the float is pitted or otherwise leaking and is therefor unable to shut off the flow to the bowl completely, and at idle you're overflowing the bowl.

Last edited by Terje; 07-22-2004 at 01:18 PM.
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  #27 (permalink)  
Old 07-22-2004, 02:52 PM
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Biggest mistake that was made 40 years ago was hotrodders installing to large of a carb. Guess what 40 years latter same mistake is made.
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Old 07-22-2004, 03:14 PM
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Rolm, What's your point? If you have a better idea then state it. Making comments like your does nothing to advance (or restore or preserve) constructive knowledge. I am a rookie at the hobby, but I'm not here to start an arguement. I'm here to learn and understand so that the hobby is more enjoyable. So, if you have a constructive comment to make, make it!
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  #29 (permalink)  
Old 07-22-2004, 03:44 PM
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Please do not feed or talk to the trolls, thank you for your cooperation.

Last edited by 4 Jaw Chuck; 07-22-2004 at 08:28 PM.
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  #30 (permalink)  
Old 07-22-2004, 03:59 PM
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Rolm, That's the carb he has, and if there's nothing wrong with it, it should work fine on his engine.

Sure it's bigger than it needs to be, but that's not a problem, and it should not be a problem.

What he wants to do is avoid spending the money on another carb.

If this carb that he has that is bigger than it needs to be was not able to opperate at 100, 200, 300, and 400 CFM, then any engine that you put this carb onto that requires 600 CFM would not run properly at half throttle or idle. This would be a problem with the carb.

Again, if the carb has no problems, it should operate fine at 100, 200, 300, and 400 CFM, so it should operate fine on his engine.
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