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Strip on friday, problem now!

7555 Views 77 Replies 18 Participants Last post by  cdahl383
I have a 77 Nova that I bought about a month ago. I have been going through it trying to get ready for the strip on Friday. I have ran into a problem that i cant seem to track down. Originally i had a Edelbrock 600 on it. I got and installed new plugs and performance wires, new thermostat, water pump, air cleaner, and rebuilt the carb.

Info: Chevy 350, Edelbrock performer rpm 6089 heads, COMP Cams Magnum Roller Rockers, Edelbrock Performer RPM 308° Intake/318° Exhaust 488''
Intake/.510'' Exhaust cam, Hooker headers, 1" carb spacer, Edelbrock performer rpm intake. Points distributor.

The problem: I had a serious engine bog at 3/4 throttle. It feels like there were dead spots in the throttle from closed to floored. I adjusted the air/ fuel screws with a vacuum gauge and the highest reading i was getting was 9 in HG at the carb. Well that really messed things up, it was dieing out at idle when i applied any gas. I went out and bought a edelbrock 750 and threw it on there last night and that solved the dieing out problem and minimized the bog problem but its still there.

1. What could be the problem?
2. Does anyone know what the degrees of timing would be?

Thank you in advance
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Set timing to 14 at idle and 36 degress total advance. You may have to play with the timing abit for best results. If this does't help try taking the carb spacer off. If you're adjustments don't help try taking the carb spacer off. RICK
You have to get a mettering rod and jet kit for the Eddy carbs and tune them. A 750 on a 350 will run like crap until you get it richened up a bit.
The problem: I had a serious engine bog at 3/4 throttle. It feels like there were dead spots in the throttle from closed to floored.
Thank you in advance
This is and has been a problem with that kind of carb since Carter use to make them. That is why if you are looking for true performance you need a Holley.
I was going to say the same, but felt bad about OP just buying new one.
This is and has been a problem with that kind of carb since Carter use to make them. That is why if you are looking for true performance you need a Holley.
I have not adjusted the air/fuel screw, or checked vacuum since I put this new carb on. Could making the mixture richer with the screws help in this case. Or would I have to get another kit like the other guy said. What exactly is the problem with edelbrock carbs?
There really isn't any problems with Edelbrock carbs. Some people do have trouble tuning them, but when they are tuned right, they run pretty well and reliable. The carb you have is a design that Edelbrock bought from Carter, so it is a pretty old design. That carb is designed more towards economy and cruising than it is towards wide open performance. A holley would have been a better choice for the strip, but the Eddy can still run fairly well.
What exactly is the problem with edelbrock carbs?
There really isn't any problems with Edelbrock carbs. Some people do have trouble tuning them.
The Edelbrock Performer Series carbs are the old Carter AFB's, Edelbrock bought the rights. The Carter AFB was used on several GM cars in the 60's including but not limited to the Pontiac GTO, Pontiac Grand Prix and the Chevy Impala with a 409. GM had numerous problems with a "bog" on those cars which is one of the reasons they stopped using them and went to the Rochester Quadrajet in '67.

So I guess GM must have been one of "those people" that had trouble tuning them.

I have always said that the Edelbrock carb is a good "street" carb with excellent street manors but sucks when it comes to performance.

I am sorry if I offended you because you just bought that carb but I just tell it like it is. Would you or anyone feel better if I was like so many others that say "yea just throw more money at it, that should do it" or would you rather hear solid info? I will never tell people what they want to hear, I'll tell them what they need to know as long as I know for sure.
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I was not aware of the bog issue GM had with the AFB, that was before my time. :hiding: I have an Edelbrock 750 on my car, and it was trouble-free when I was driving the car daily. I don't recall ever having a bog issue, so maybe I'm just lucky. I do know that a 750 out of the box needs to have the rods and jets changed to run well on a mild 350.:yes:
Yes absolutely run the vaccume gauge and properly set the carb up to run at an optimal fuel ratio. There's many videos on you tube to help get this done. If you rebuilt the first carb, then this should not be an issue for you. I would run all four or five different tests you can run with the gage. You'll find out if you have a vaccume leak, or if the needle is bouncing or behaving a certain way , what to do... I bought one new last year and saved the back, it illustrated many tips... There's no reason the edelbrock carb you have won't perform very well both street n strip. Especially since you have a mild manor performance 350. I have the 1407 and it gets driven everyday on my 355. I love the way you can feel the secondaries when they open at full throttle. I had to lighten the springs and adjust the accelerator pump linkage. I had bog off idle but its gone now, for the most part, lol. I'm sure there is superior carbs, but edelbrock is a great company and the design has been around for ages. Even the newest demon carb left the Holley design behind and went with the carter, having no gaskets below fuel line. Plus you can make so many adjustments without taking the carb off the car. You can also turn them into double pumpers and people driving 1000 plus HP drag cars win with them so it can be done. Rock it out bud, the track can help tune it too. Go and have fun
Answer 1) needs tuned
2) I don't think anyone can tell you your timing, you should however follow the advise of starting with 14 initial and 34_36? Total and adjust accordingly. Some like a Lil more I believe, but everyones set up is a Lil different. Plus gas varies, get her close tho and shell tell you what she wants!
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I was not aware of the bog issue GM had with the AFB, that was before my time. :hiding: I have an Edelbrock 750 on my car, and it was trouble-free when I was driving the car daily. I don't recall ever having a bog issue, so maybe I'm just lucky. I do know that a 750 out of the box needs to have the rods and jets changed to run well on a mild 350.:yes:
Do you have a link I could check out for the jets and rods, or maybe a size jet i should be looking for? I
I'm pretty sure the edelbrock site offers a pdf file you can download that will have a graph or chart that will tell you what kit to buy. There like 45 bucks and will allow you to change within a fairly wide range of settings.
The link that sevenzeronova posted is to the manual for the carb, if you didn't get one with the carb. It has instructions for tuning, and I think it should have a part number for the tuning kit. It's really not possible for me to tell you what rod and jet combination to use because of differences in altitude etc. affect how the carb works.
I was not aware of the bog issue GM had with the AFB, that was before my time. :hiding:
:slap: :slap: :slap:

I have an Edelbrock 750 on my car, and it was trouble-free when I was driving the car daily. I don't recall ever having a bog issue, so maybe I'm just lucky. I do know that a 750 out of the box needs to have the rods and jets changed to run well on a mild 350.:yes:
Unless it's a custom built carb, they pretty much all need to be played with. Even a custom built carb may need some fine tuning. :yes:
Thanks all. I know the direction i need to travel in now.
First of all, make sure your timing is set properly for your engine setup. If you have a more aggressive cam/setup you may need more initial timing. I'm running 16 initial and total at 32 degrees, seems to work good for my setup. Before when I had it at 10 initial and 22 mechanical for 32 total it ran good at WOT but the low end sucked. Definite hesitation/bogging off idle.

Lots of people complain about Edelbrock carbs not working well but I think you can get them to work great with some tuning/time. Holley is probably the better bet for the dragstrip, they have better tuning capabilities/options for dialing your car in really good at the track. But if you're like me and only go to the track occasionally for a few blasts a year and spend most of your time on the street, a properly setup Eddy carb should be fine, especially since you just bought a new 750.

I had hesitation issues with my Eddy carb as well when I first bolted it on. It ran pretty good out of the box, but definitely had some annoying issues that needed to be addressed.

First of all, make sure the float levels are correct. They are out of spec usually from the factory from bouncing around in dry bowls during shipping. Mine weren't too far off, but they weren't right. Set them to 7/16" float level and 15/16" to 1" float drop.

Second, make sure you are running no more than 5.5 psi of fuel pressure. Eddy carbs do not work well with more than 5.5 psi of fuel pressure, tend to flood, run rich, etc.

Off idle hesitation was the most annoying. More initial timing helped clear most of that up. Went from 10 BTDC to 16 BTDC and limited my mechanical in the distributor to arrive at the same total timing figure.

Then I found I had to go to the next size up squirters. I believe a 750 has a .035" squirter stock similar to what was stock in my Eddy 800 AVS carb. I went to the .043" squirter and adjusted the accelerator pump by moving it to the middle hole and the car ran much better off idle.

Then you want to make sure you have your idle mixture screws adjusted for maximum vacuum. Just hook up a vacuum gauge and turn each one until you get the highest vacuum reading and repeat for the other side. Then adjust your idle speed again to whatever RPM you desire.

If you have a bog when you step into it at part throttle, this is probably due to too light of a step-up spring for your metering rods. I never had any luck with the lighter springs. I always used the strongest spring (silver 8" hg) and sometimes even stretched it out slightly. When I put that spring in the car, my part throttle hesitation was gone immediately.

If you have a bog transitioning from the primaries to the secondaries when you step into it from part throttle to full throttle, that is probably the secondaries opening up too soon, causing a temporary lean bog since its sucking in air too soon before the fuel can catch up to it. On a 650 or 800 AVS you can adjust this easily by turning the AVS screw on the carb, this adjusts the tension on the spring that controls when the airflap opens up.

On a 600 or 750 Performer carb you are more limited in that the secondaries are controlled by counterweights. I was fortunate enough to have good luck with my 750 on my car in this area right out of the box. But if you're having issues, you may have to try messing with these weights. I've never done that myself, so I cant help you much there. I have read where guys have taken them out, shaved weight off to make them open sooner, or added weight (I guess welding stuff on or something) to make them open slower. This is the part of the Performer Series carbs that sucks, tuning this is kind of a pain.

Your timing curve is also important. Too much timing too soon can cause issues too. If you have really light springs and really heavy weights in your distributor, that can throw all your timing in way too soon before your engine can handle it and cause problems as well. But it sounds like you have that under control so I doubt thats the problem.

I would try to do these things above and see if that helps at all. Maybe someone else with some experience tuning the counterweights on the 750 carb can chime in and help you with that one.

But if I were you, I'd tackle these things first:

1.) Run as much initial timing as you can while ensuring correct total timing.
2.) Verify and/or adjust floats in carb
3.) Adjust idle mixture for highest vacuum reading
4.) Adjust accelerator pump to middle or top hole to ensure proper shot
5.) Try using stronger step up springs (may have to order separately)
6.) Try running vacuum advance to manifold port
7.) Change distributor springs to bring timing all in around 2800-3200 RPM

See if that stuff helps at all. If not, then its probably an issue with those counterweights and the secondaries opening too quickly causing a lean bog. There are other threads out on the internet about how to correct this as well, but as I said I never had to mess with this so I can't help you there.

If youre going to be at the strip a lot a Holley carb is probably a better bet, but you just bought the new Eddy 750 so might as well try to get that running correctly first before tossing that aside.

Hope some of my ramblings help, haha!
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Good advice^
That was great advice cdahl383. I see your in Detroit, that's right around the corner. I have absolutely no knowledge on distributors or any sort of electronic issues. Which way would I turn it to advance the ignition? Also you mentioned something about slightly stretching the spring out instead of locating a new one. It seems like it bogs when the secondaries open. At WOT it continues to shudder but accelerates slightly. She hauls *** until just after half throttle then comes the bog. There is a sweet spot in the throttle where its nice but it would be awesome to be able to stomp on it and run the engines true potential. Id hate to see a nova get passed by a Honda civic at the track, lol.
I just installed a fuel pressure gauge on my line it reads an average about 9 to 10 psi. Since you said nothing over 5.5 psi, is there any way i can back off that fuel pressure, and could that factor into my problem.
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Well I'm by no means an expert either, I've just dealt with a few of these issues before on my own car so hopefully some of this stuff will help you as well.

It sounds like you have way too much fuel pressure for an Edelbrock carburetor. It'll say right in the manual that you should not have anything over 6 psi, ideally around 5 to 5.5 psi. I'm running a mechanical Edelbrock fuel pump that puts out 5.5 psi so I never had to deal with a fuel pressure regulator. You should be able to buy a regulator and hook it up before your carb to dial your pressure down to 5.5 psi or so. I never had to do this before so I cant help you much there, but this should be a relatively common thing that people do, so you might be able to get some help from others on here for that or do some searches on here or on other websites as well. Bottom line, you need to get the correct fuel pressure for this carburetor or it will never act correctly.

I'm no carb expert, but my guess is that with 9-10 psi of pressure, when you go WOT the pump is flooding the carb, the float bowls are being overwhelmed along with the needle and seats and the carb can no longer meter the fuel correctly, causing the goofy stuff thats going on when you step on it.

So I'd say step 1, get fuel pressure under control, regulate it to 5.5 psi.

It sounds like you are not too familiar with distributors/timing so the first thing you'll need to do is get a timing light if you dont already have one. There are a couple types of lights you can get, either an inductive or a dialback. An inductive is probably the best bet, this will be cheaper too. You can also get a dialback which has some additional features. Either way, get a timing light for sure, or maybe try to borrow one from a buddy if you can if you cant get one on your own just yet for whatever reason.

There are three components to your timing.

1.) Initial (dependent upon where you physically lock down the distributor)
2.) Mechanical (functions by weights, center plate, and springs under rotor in the distributor)
3.) Vacuum advance (adds or subtracts degrees of timing at various rates/limits based on vacuum produced by motor at different times)

The first two added together are considered your total timing. When guys say my total timing is 34 degrees all in at 3000 RPM, they are saying their initial plus mechanical is 34 and it is all there at 3000 RPM and does not advance any further from that point.

Vacuum advance is used to aid part throttle response, in some cases aid in better idling, and to help the engine run cooler and get slightly better fuel economy. If you have a street car, you should try to run vacuum advance.

Now that you know a little about timing, you can now hook up your timing light and check to see where you're engine is currently set at. For example, you hook up your light and it says 6 BTDC when you point it at your damper while the car is running at idle. This means you have 6 degrees of initial timing.

Now, the next step is to determine what your total timing is. This is where having a degreed damper or dialback light is helpful. With a degreed damper, you can put a mark at say 32 or 36 and rev the motor up and check for this mark to line up with 0 on your timing tab when you point your timing light at it. If the 36 degree mark on your damper lines up with 0 when you rev it up and it does not go further than this with further increase in RPM, then you have verified your total timing.

Most GM HEI distributors put out around 22-24 degrees of mechanical advance. That is, the weights in the distributor spin out far enough to advance the timing another 22-24 degrees as RPMs increase.

So as an example, if you have 6 degrees initial, and you have 24 degrees mechanical, you have 30 degrees total timing. This is probably a little low, though every engine is different so you must experiment with this. Most sbc's like around 32-36 degrees of total timing, but this varies from engine to engine, so dont view this as set in stone for your car. Just an illustration for you.

The initial can be changed by physically turning your distributor clockwise or counter clockwise. If you want to advance your timing, you want to turn it counter clockwise. If you want to retard the timing, then turn it clockwise.

The mechanical advance is handled by the internals of the distributor and can be adjusted for both RATE and LIMIT. The springs on the weights control the RATE of advance. The center plate the weights butt up against control the LIMIT of advance. Generally, stock distributors have heavy springs which have a SLOW rate of advance. This sucks for performance. Changing the springs to lighter springs will bring the advance in sooner for better performance. However, too soon can be bad as well as this may cause detonation. If you start with all in at 3000 or 3500 RPM that should be a good starting point. Then you can experiment with sooner curves if you'd like.

Larger cams and high performance engines tend to like more initial timing than stock engines with smaller duration cams. For example, my car runs better with 16 initial and 16 mechanical for 32 total than it does with 9 initial and 23 mechanical and 32 total. Same total, different advance curve. You'll have to experiment with what your car likes best.

Now that you have a little background, you can go out and test what your timing settings are currently. Write this stuff down, and see where you're at. What is your initial? What is your total (i.e. when you rev it up, etc)? You want to make sure this is setup correctly FIRST before trying to tune your carb too much.

CARBURETOR: Your best bet with an Edelbrock carburetor that you want to tune is to by the calibration kit. You can find this at some parts stores or online. They run around $40-$50. They come with an assortment of jets, rods, springs, etc. Then you'll want to download the Edelbrock carburetor manual and print this off, towards the end is a tuning guide that provides guidelines for tuning leaner, richer, power or cruise modes, etc. Without the manual you're in the dark, and without the calibration kit, you're stuck with whatever parts are currently in your carb, which may not be optimal.

Every Eddy carb I've had has had too light of step up springs in them. These control when the metering rods move up out of the jet to allow more fuel in for power mode. Too light of spring, and the rod will not move quickly enough, causing a lean hesitation/bog at part throttle tip in. Too strong of a spring will not allow the rod to sit back down into the jet, causing too much fuel to pass through the jet at cruise mode or idle. You want to have the appropriate spring in there so the rods move up and down at the appropriate times when you step on the gas. I've found that the strongest spring (silver 8") or the second strongest spring (pink 7") work the best, at least on my engines. These various springs will be included in the calibration kit and you can easily change them with the carburetor mounted on the car.

The WOT tuning may be more of a hassle because the Performer Series carb you have used weights to control the opening of the secondaries. The newer AVS style carbs are roughly the same except that you can tune the WOT settings a little easier by turning a screw that adjusts the tension for how soon the airflap opens.

What you need to do first is get your fuel pressure down to 5.5 psi. Then you should take the carb off and check your float level and float drop and adjust them to proper spec.

Then make sure your timing is set correctly. For example, you could try using 12 initial which would probably give you around 32-36 total depending on what your distributor is putting out. I cant determine that here, so you'll have to figure that out on your own. Until you get everything sorted out I would err on the conservative side and try 32-34 total. You can try more advanced settings like 36-38 later once you have everything else running correctly. Better to be a little under than over and have detonation issues, at least until you get a chance to experiment more.

I realize this is probably information overload, but read through it and see if it helps you out at all. It should at least get you started.

Main thing is, regulate your fuel pressure to 5.5 psi from your current 9-10 psi and that should help out big time. Let us know how your car runs after you do this and then you can go from there.

Hope that helps, sorry for the novel! Haha!
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