Edelbrock 600 carb issue?

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Optik

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Need help with what I think is a carb issue? I'm running a '77 360 with a stock bottom end and heads, Holley Street Dominator intake, headers, somewhat lumpy can (233 @ .050, .512 lift), and an edelbrock 600 model 1406 carb in a 64 Dart with built A999 and 2.93 geared 8 3/4. Car has a nasty hesitation/stumble when I'm barely on the throttle at takeoff or cruise. Goes away when you give it more gas. I believe I have the timing correct, car seems to like about 18* initial with about 34* all in by 3000rpm. Ran fine for almost 20000 miles but has developed this issue recently. I've been able to affect it somewhat with idle mixture and slight timing adjustments but cannot tune it out completely. Have not yet taken the carb apart and my next step will be to pull and try to read the plugs. Anyone have any advice or experiencing similar issue?
Thanks,
-Tim
 
What you have so far is a new carb on top right?
Start the tuning with a plug reading in which I think you'll find lean and richer the mixture up. If it stumbles when you hit the gas, add more
Pump shot.

There is no carb issue yet since you have not started to tune it.
 
How old is the carb ? does the car sit for long periods? Mine is the older Carter comp series with a leather accelerator pump and when it sits and dries out it takes days for the stumble to go away till it swells again.Sometimes I have to prime to get it started because of no squirt. I should say that it squirts intermittently or dribbles,not a good strong squirt. Until it does, stumble city. Just a thought.
 
The carb is about 6 years old and has about 20k miles on it. This is one of two daily drivers so it doesn't sit for more than a day or two at a time without being ran. Gas tank and fuel lines were all brand new and added when the carb was installed. It ran great up for years until about two weeks ago when this started. Fuel filter is clean. I did have to recently replace the vacuum advance can but that has had no effect on the stumble/hesitation either way.

Will report back with a plug reading once I get a chance to pull them. Working on this thing on my lunch breaks so would like to try the easy/quick suggestions first before taking the carb apart.

Thank you!
-Tim
 
That leather part needs to be replaced. There no longer leather
 
Here is a photo of one of the plugs. I know, they are almost completely ashes over so I wire-wheeled them and put them back in and did not help the issue. Underneath all the deposits they looked to be in good condition. Today checked the metering rods and they are stock 74-57. Haven't disassembled carb yet but a carb rebuild is my next try at fixing this, hopefully this weekend. If that doesn't fix what would be the next thing to look at?
 

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Ash deposits are usually from poor fuel or additives. Can also come from some leakage in the guides. Not that it help's the hesitation issue....As far as that, i was thinking pump shot also.
 
Since you pulled the metering rods, clean the bores and pistons with carb cleaner.Litely with 1200 sand paper clean the pistons and check for free movement when you reassemble.Some guys clean and check this area every couple months as sometimes they will start to hang up. Just a thought.

Also with spark plugs you want the center electrode to have sharp edges with a flat top.Looking at yours you can see that it is rounded(normal wear). Compare it to a new plug and you will see what I mean.
Again this may not help your problem but is things to look for when it comes to tuneup.
 
x99

accelerator pump...$13.99 at O'Rielly's....on the shelf.
I'd definetly replace that.

Never hurts to do a Ignition Tune Up either....that plug looked like crap.

You might pop the distributor cap, chunk it and the rotor, replace with new and go through all the plugs and wires....then:

Set/Check Initial Timing.
Set Curb Idle and rebalance your Air/Fuel mixture screws.

http://www.edelbrock.com/automotive_new/misc/tech_center/install/carb_faq.shtml

best of luck.
 
Took the top off the carb today to check the accelerator pump and it seemed to be in working order, no tears or holes in the rubber and i was able to get a good pump shot through the squatters by pressing down on it by hand. Some more observations - while indications are that it's a lean issue, the motor actually seems to want much LESS fuel at idle. By opening the lower vacuum port it smoothed the idle way out and picked up a lot of rpm. I will still plan on accelerator pump replacement and see if that helps and report back.
Thanks for all the suggestions so far!!
-Tim
 
Rebuilt the carb today. Tons of stuff was way off stock specs according to the instructions in the kit. Will put the carb back on in the morning and see how it runs. It's always been a gas hog, apparently because the secondaries were set to open way too early. Float levels were way off and uneven side-to-side. Not sure if any of this was causing my issue but I'll see how it runs tomorrow and report back.
 
Carb rebuild made no difference. I was extremely careful to clean and blow out all passages and re-install everything correctly, an it seems to be working Ok or at least as good as before. At the best idle settings (set with a vacuum gauge) the motor seems to be running EXTREMELY rich, but on takeoff it acts like its not getting any fuel. Accelerator pump seems to provide a nice shot through all range of throttle motion and of I create a vacuum leak, such as by taking off the manifold vacuum cap or PCV hose at the carb, I definitely picks up rpm (+500 rpm with PCV hose off). It pulled almost 15" of vacuum idling at about 1000rpm in normal configuration. I even drove it without the PCV connected and port opened and it acted the same way. Timing checks out as normal, still likes about 18* initial. I guess the next step is to replace plugs/wires/cap/rotor and see if that helps but I just hate throwing parts or money at this without tracking down the cause. Could the fuel pump be the culprit? It only took about three cranks for it to fill the carb bowls enough to get a shot by cracking the throttle, and I was VERY careful to set the floats correctly. Plus I don't see how it could be the fuel pump if it's acting like it wants gas only at initial throttle and runs better when I mash it. Could this be a mechanical problem like a stuck or bent valve? Is it also possible that a faulty PCV valve could be to blame? I did notice that at one point the PCV was kind of "humming" or whistling and I could feel it vibrating rapidly, yet this was also not steady but came and went. The only other thing I was thinking was either the balance ring has slipped or I've got a broken spring in the distributor.
Needless to say I am SUPER frustrated with this and can't afford to take it to someone else right now and need to fix soon so I can drive this thing to work.
Thanks for the help and suggestions so far! If anyone in the Cincinnati OH area wants to come by and give me a hand with this it would be much appreciated and I can offer you beer and maybe lunch or something. :)
-Tim
 
Do you have access to another carb, just for testing purposes? That would at least eliminate or confirm whether it's the carb or some other problem. I have heard of carbs having casting issues internally, which can cause problems.
 
Have you changed the metering rods and step up springs? They make a kit for that. I changed mine on my carb (it's a 1406) just like yours. It made a world of difference. Also there are 3 different positions you can adjust the accelerator pump. Have you looked at that. Mine was set at the top and it was getting too much fuel. I moved it to the middle and it's running a lot smoother with no hesitation.
 
There's the old trick of partially covering the intake with your hand when you start the RPM's up to see if it actually is lean or rich.
Partially cover the carb intake with your hand when you open the throttle.
Is it worse or better when you do it?
 
Tried accelerator pump lever in all positions systematically and it does not fix. Have also tried covering the carb and that does not fix. It does have 1 step up on primary jets which I did years ago when we dyno'ed it early on after the v8 swap and it's run fine in its current configuration for years. Took it to a buddy's earlier and we fiddled and twiddled with it for a while with some sucess - the hesitation is still there but less severe. My friend is thinking ignition and not carb. Replacing cap/rotor/plugs/wires later today and will report back. If that doesn't help I'll get the calibration kit and change the step-up springs. One thing at a time. Thanks again everyone for the input!!!
-Tim
 
If anyone in the Cincinnati OH area wants to come by and give me a hand with this it would be much appreciated and I can offer you beer and maybe lunch or something. :icon_smi:
Click to expand...

The closest I get to Cinci is your radio station...WLW 700 "The Big One"...on the internet.
 
Ignition tune-up (cap/rotor/plugs/wires) made no change. Called Edelbrock tech and they were not much help although nice enough. Their only recommendation was to put some fuel system cleaner in the tank and see if that helped. I guess I will try that although it sounds like a shot in the dark. Next step I suppose will be to try changing the step-up springs to a lighter spring and see what that does. Tech recommended the orange or pink springs (5 and 7) respectively since the car motor pulls 13-15" of vacuum at idle depending on the mixture adjustment. Idle mixture has seemingly no effect on the problem though. After re-reading the edelbrock manual, I'm thinking that the problem lies somewhere in the transition from the idle system to the primary metering system. Any thoughts??
Thanks,
-Tim
 
Take the booster venturies out of the primaries and clean them.......I have had very similar problems with almost new carbs that have set for a while, and have been plugged by dirt and such in the air bleeds, and different places. Clean the carb, and it runs good as new. If there is any dirt in the transition circuit or air bleeds the carb will definitely not run right. Especially if the lean spot/hesitation is right off idle and adding to the pump shot does not help.
 
65Val said:
Do you have access to another carb, just for testing purposes? That would at least eliminate or confirm whether it's the carb or some other problem. .
Click to expand...
this is what i would do to rule out the carb as the problem before going any further. you may end up replacing a bunch of parts and end up with the same problem.
 
I THOUGHT I had cleaned out all the booster assemblies really well but I will pull the primary ones and soak and clean them again. I suspect that is where the problem lies, especially since that is the basis of the transition between idle and primary circuits in the edelbrocks. Hopefully that is the fix. Unfortunately at this time I don't have another known good carb to try or access to one without buying a new one and I don't want to spend that money on it. Everything I've bought new so far was probably necessary or due for replacement anyway so I'm ok with those expenses but the wife will certainly be PO'ed if a new carb shows up at the door LOL!!!
 
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