General mild roughness...help?
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Joined: Sep 2004
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From: Madison WI
General mild roughness...help?
Hey guys, I've had a small problem with my 72 L-48 ever since I swapped on the Holley carb (SA 670). It really seems like the kind of thing that could be easily cured with a little carb tuning, but I have very little experience with carbs, so I definitely need to learn some more before I start tinkering with things. Anyway, my problem is that the engine simply doesn't run terribly smooth - I'll get a little hesitation on acceleration, and even while cruising I get little jolts of hesitation somewhat often. I think it's worse when the engine is cold, but that's hard to say for sure just because it's been so long since I got to drive the car (stupid WI winters!). Anyway, what could be my problem?
As an aside, I really want to learn more about carbs and how to tune them...any good resources you guys recommend? Thanks in advance!
As an aside, I really want to learn more about carbs and how to tune them...any good resources you guys recommend? Thanks in advance!
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Joined: Jan 2002
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From: Marietta ga
If you need some good solid advice, this is the place. I would start by listing all of your engine specs (parts and setup).
If you are looking for tuning advice for carbs I would suggest going here
http://wiki.corvettefaq.com/index.php?title=Main_Page
good luck
If you are looking for tuning advice for carbs I would suggest going here
http://wiki.corvettefaq.com/index.php?title=Main_Page
good luck
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Joined: Sep 2004
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From: Madison WI
Thanks for the response 
. The car is pretty much stock:
Stock bottom end 72 L-48
Edelbrock Torker I (yes, the original from the 60's) intake
Holley SA 670
Headers/true duals
Mallory Unilite electronic ignition
Pretty much it as far as anything that could be relevant. Stock fuel pump routed through stainless steel braid and an ungodly number of AN adapters coming off the pump
. The car is pretty much stock:Stock bottom end 72 L-48
Edelbrock Torker I (yes, the original from the 60's) intake
Holley SA 670
Headers/true duals
Mallory Unilite electronic ignition
Pretty much it as far as anything that could be relevant. Stock fuel pump routed through stainless steel braid and an ungodly number of AN adapters coming off the pump
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From: Madison WI
Definitely seems to be hesitating more than stumbling (I'll just get a small hesitation and then it'll take off), and it happens whether its under light or hard acceleration. Like I said, I'll also get slight "jolts" of hesitation when just cruising under constant pedal pressure. Nothing unusual about exhaust color, and nothing like black smoke being blown out. I'll have to call the shop that worked on my car (frame repairs and a couple minor things I had them fix while it was in) to determine timing; I just had them set it to whatever they felt would be best and don't exactly remember 
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From: Madison WI
I called the shop today, and unfortunately they don't know exactly what the timing was set to. The manager/owner explained to me that rather than just set to a predetermined level of advance/retard, they just tune it until it runs optimally...which makes me think it's probably not significant in my problem...
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Originally Posted by 72Tornado
I called the shop today, and unfortunately they don't know exactly what the timing was set to. The manager/owner explained to me that rather than just set to a predetermined level of advance/retard, they just tune it until it runs optimally...which makes me think it's probably not significant in my problem...
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From: Madison WI
I'll definitely do some reading about the topic...but the thing is, I never had this problem with the old Q-jet on there. Since putting on the Holley, I've had the problem both before and after the shop worked on it (admittedly, it started and ran a helluva lot smoother after they worked on it, but timing wasn't the only thing that was fixed). I suppose I'm just inclined to believe it's something other than timing...
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Joined: Jan 2006
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From: Canton Georgia
Isn't a Torker a single plane intake? I would think that may be the problem. The carb is not seeing enough signal at the lower RPM's and leaning out. The Q-Jet would see a higher velocity through the smaller front two barrels and work OK. But the holley has larger front barrels, and a different metering system. I would recommend going to a dual plane intake. My experience with vacuum secondary carbs is they are very close out of the box. Unless your carb has screw in air bleeds, the factory settings are very close to optimum.
Also, your single plane is reducing your fuel economy......torque and driveability would be better with a dual plane intake.
Also, your single plane is reducing your fuel economy......torque and driveability would be better with a dual plane intake.
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From: Madison WI
Originally Posted by VintageMuscle
Isn't a Torker a single plane intake? I would think that may be the problem. The carb is not seeing enough signal at the lower RPM's and leaning out. The Q-Jet would see a higher velocity through the smaller front two barrels and work OK. But the holley has larger front barrels, and a different metering system. I would recommend going to a dual plane intake. My experience with vacuum secondary carbs is they are very close out of the box. Unless your carb has screw in air bleeds, the factory settings are very close to optimum.
Also, your single plane is reducing your fuel economy......torque and driveability would be better with a dual plane intake.
Also, your single plane is reducing your fuel economy......torque and driveability would be better with a dual plane intake.
On a more general note, excuse my ignorance, but what about the dual plane would solve this problem? I understand your description of too low a velocity, I just don't understand how switching to the dual-plane would fix it...
Last edited by 72Tornado; Feb 16, 2006 at 03:41 PM.
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Joined: Jan 2006
Posts: 72
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From: Canton Georgia
The dual plane sends a much stronger signal to the carbueretor at low RPM's and improves the low RPM driveability, and PROBABLY will solve your hesitation problems.
If your going with an Air Gap soon, you are on your way to solving this. I wouldn't start messing with the carb until I had a dual plane on it.
Also, I was not slammin you because of the torker...not my style.
You catch more flys with honey than with vinegar.....
If your going with an Air Gap soon, you are on your way to solving this. I wouldn't start messing with the carb until I had a dual plane on it.
Also, I was not slammin you because of the torker...not my style.
You catch more flys with honey than with vinegar.....
Burning Brakes
Joined: Aug 2005
Posts: 1,126
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From: Hudson Falls, N.Y. 76 Vette Modified L-48
Personally...before I would start swapping intakes and carbs, and doing all this major overhalls...I would start small (being the "mechanics?" don't "remember?" what they set the timing at?), make sure the timing is full in to 36* at 2000-2500 rpm....recurve the distributor with some new springs, being it's a 72, make sure the mechanical advance isn't rusted up (like my 76 was) and also that your vacuum advance is working and tune idle mixture for max vacuum, I'd look around the net for an article specific to your carb as far as adjusting the idle...they are out there (having dual carbs on my 76, trust me, they are a bear, and I found an article)....THEN, if you still have a problem, turn to swapping parts...just my 2 cents 
Melting Slicks
Joined: Dec 2005
Posts: 2,441
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Hey guys, I've had a small problem with my 72 L-48 ever since I swapped on the Holley carb...
... they don't know exactly what the timing was set to. The manager/owner explained to me that rather than just set to a predetermined level of advance/retard, they just tune it until it runs optimally...which makes me think it's probably not significant in my problem...
These are the key statements; the car needs the timing set properly. All cars have specific timing values that need to be closely followed for proper drivability, the timing setting is easily checked and could solve your problem. If after the timing is set you are still experiencing the problem, the symptoms you describe also sound as though the carb is lean in the part throttle condition. Your intake worked fine with the previous carb so it shouldn't be an issue.
... they don't know exactly what the timing was set to. The manager/owner explained to me that rather than just set to a predetermined level of advance/retard, they just tune it until it runs optimally...which makes me think it's probably not significant in my problem...
These are the key statements; the car needs the timing set properly. All cars have specific timing values that need to be closely followed for proper drivability, the timing setting is easily checked and could solve your problem. If after the timing is set you are still experiencing the problem, the symptoms you describe also sound as though the carb is lean in the part throttle condition. Your intake worked fine with the previous carb so it shouldn't be an issue.
Instructor
Joined: Jun 2003
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From: Rittman oh
Originally Posted by 72Tornado
Hey guys, I've had a small problem with my 72 L-48 ever since I swapped on the Holley carb (SA 670). It really seems like the kind of thing that could be easily cured with a little carb tuning, but I have very little experience with carbs, so I definitely need to learn some more before I start tinkering with things. Anyway, my problem is that the engine simply doesn't run terribly smooth - I'll get a little hesitation on acceleration, and even while cruising I get little jolts of hesitation somewhat often. I think it's worse when the engine is cold, but that's hard to say for sure just because it's been so long since I got to drive the car (stupid WI winters!). Anyway, what could be my problem?
As an aside, I really want to learn more about carbs and how to tune them...any good resources you guys recommend? Thanks in advance!
As an aside, I really want to learn more about carbs and how to tune them...any good resources you guys recommend? Thanks in advance!
