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I will try to explain an issue on my C3 '69 manual. the carburator is an edelbrock
with high rpm the engine is very nice but if I take my foot off the accelerator and the re-throttle, the engine sobs for 1-2 seconds and then revs correctly.
any idea to find the root cause?
Did you check the point dwell?
Did you check the timing?
Did you adjust the idle mixture screws?
Did you check for a vacuum leak?
What model Edelbrock carburetor is it?
Just went through a similar problem on one of our vehicles. Sometimes getting on the accelerator would yield instant revs, sometimes not. Turned out to be the accelerator pump in the carb. It was intermittently sticking and sometimes would spray gas when we hit the pedal, sometimes not.
I would order a Carburetor Rebuild kit and go to work! There were plenty of parts in the carburetor that didn't like ethanol. This oxygenated fuel is really rough on accelerator pump diaphragms.
It doesn't take too long to rebuild one of these old Edlebrock Carburetors and most of the parts are still very available.
A better choice would be to have someone like Lars rebuild it and set it up for you.
2020 Corvette of the Year Finalist (performance mods)
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it could be a lean bog. It is what is referred to the quadrabog and edelbrock had the same issue on their early 4 barrels carbs. The early edelbrocks have an air fuel door that is not adjustable, the newer AVS carbs do. The quadrajets have an adjustment on the air door that will make it go away as well if its not the accelerator pump..Do as suggested with a rebuild. Edelbrocks square bores are easy to rebuild. THe edelbrock quadrajets are the same as a quadrajet to rebuild, you just need to get the cliff Ruggles book. Rebuild it, then take a second look at it and go from there
I would order a Carburetor Rebuild kit and go to work! There were plenty of parts in the carburetor that didn't like ethanol. This oxygenated fuel is really rough on accelerator pump diaphragms.
It doesn't take too long to rebuild one of these old Edlebrock Carburetors and most of the parts are still very available.
A better choice would be to have someone like Lars rebuild it and set it up for you.
Lars will not touch an Edelbrock......there isn't a lot to them.....I can tear one down, dip, ultrasonic and reassemble in about 4 hours (3 hours for dip and Ultrasonic).
thank you very much for your helps. I will work on this and I will give you a feedback.
at the moment the ignition time in the idle is 18°. is it correct as value? I tried to decrease until 10° without change.
thank you very much for your helps. I will work on this and I will give you a feedback.
at the moment the ignition time in the idle is 18°. is it correct as value? I tried to decrease until 10° without change.
i will check the carburator.
what does means OP in the MelWff's message?
thank you
OP=Original Poster, you.
Is the distributor modified, different springs or weights?
Factory timing would not be 18.
Did you disconnect the vacuum advance when you checked it?
OP=Original Poster, you.
Is the distributor modified, different springs or weights?
Factory timing would not be 18.
Did you disconnect the vacuum advance when you checked it?
ok.
the distributor is not the original and the carburator is a type without the vacuum advance
No doubt there's a lot that others will see. My quick observations:
You have a looping, pressurized, rubber hose leading from your fuel filter to your carb. This is a huge fire hazard, but also very common. Your return line also leaves pressurized rubber hose in the engine compartment.
It looks like some of the functions of that carburetor have been removed or disabled. Is your choke always open? Secondary flappers always open? I'm no expert on Edelbrock carbs.
There are at least two capped vacuum ports on the front of that carb. One of them should have manifold vacuum that can go to a vacuum can on your distributor. You may be able to add a vacuum can (either the "correct" one, or adjustable).
thank you. I bought this Corvette 1 month ago. I have to well understand what wrong, what missing and then correct these. I will greatly appreciate all the tips and errors you will notice so that I can then correct them. in the meanstime, i just bought a couple of books about the carburator.... tomorrow, amazon will delivery at home
unfortunaly in Italy at the moment I cannot find very expert people
There should be a metal actuator on the side of the distributor. That is the vacuum advance can which adjusts ignition timing when the throttle is closed or low. That should be connected via rubber hose to the capped vacuum outlet on the front of carb on passenger's side. This is a very important feature for normal driving conditions.
Study on 'ignition timing' so that you understand what it is and how the mechanical and vacuum advance features in the distributor work and how to adjust them.
There should be a metal actuator on the side of the distributor. That is the vacuum advance can which adjusts ignition timing when the throttle is closed or low. That should be connected via rubber hose to the capped vacuum outlet on the front of carb on passenger's side. This is a very important feature for normal driving conditions.
Study on 'ignition timing' so that you understand what it is and how the mechanical and vacuum advance features in the distributor work and how to adjust them.
no, unfortunally this vacuum advance is missing. I post some pics to be sure to well understood.
no connection between the distributor and the carburator. I guess this distributor has been placed by the previous owner
There are some who believe that the vacuum advance is something you do NOT want, if you have a "performance" machine. That is a total load of B.S. The vacuum advance does NOTHING when you have the accelerator pedal to the floor! But, it allows the vehicle to start easily, have a smooth and efficient idle, and won't eat a lot of fuel just sitting there at idle.
There are some engines which, because of the radical cam and internal components, get little to no benefit from the vacuum advance. These engines have very little vacuum when idling at 1000 rpm [or higher] anyway. If that is what you have...and what you want....just keep it as is.
the issue seems to related at the accelerator pump. yesterday I changed the hole in the leverage (sorry I don't know the correct name....see picture below) and now it woks better. is not perfect yet... I will buy a kit to
restore the pump.
That's the right approach!
Fix one thing at a time. And learn how to do it yourself.
There are very few mechanics around anymore that understand these old carbs & mechanical distributor advance systems. Pre 1980 before fuel injection went rampant. Most of the current repair shops do not, even here in the states. Even here you have to find a very experienced independent mechanic that grew up with these cars in the 70s & 80s, that is still working, and most of those guys are 60+ years old now. My guy just had a stroke.
Fortunately there are quite a few of us on this forum, who love these cars, and some of us are pretty good amatuer hobbyists, and a few are professionals. So I have found this to be the single best place for advice, outside of a printed book, or my one trusted friend.
So ask away!
Personally, I have a special soft spot for someone trying to keep one of these old cars running in another country 6,000 miles away, with even less resources than we have here stateside!
carburator issue?
