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I'm getting some slight hesitation off the line and some popping thru the exhaust. I've been told by 2 different mechanics that my '64 327-300, manual trans should be receiving vacuum from the manifold, not the carb (as I have it). Is this true? If so, is this where the vacuum connects? (see pic below). Thanks for the input and have a safe and happy 4th.
If you're drawing vacuum from below the carb's throttle plates (e.g. the carb's base) that IS full manifold vacuum...you don't show a picture of the carb...
There are 1/2 dozen reasons for your symptoms. Vacuum advance's chief benefit is at cruise - you can plug the vacuum source and drive the car and see if you get the same symptoms...
Last edited by Frankie the Fink; Jul 2, 2018 at 10:05 AM.
If you're drawing vacuum from below the carb's throttle plates (e.g. the carb's base) that IS full manifold vacuum...you don't show a picture of the carb...
There are 1/2 dozen reasons for your symptoms. Vacuum advance's chief benefit is at cruise - you can plug the vacuum source and drive the car and see if you get the same symptoms...
I have a general question. Is the tapped hole in your carb spacer plugged? It appears from the photo it is open which would be one hell of a vacuum leak.
I have a general question. Is the tapped hole in your carb spacer plugged? It appears from the photo it is open which would be one hell of a vacuum leak.
I saw that but I assumed the car would run so damn bad with that hole wide open to the atmosphere it'd be obvious -- maybe I shouldn't have...
I have a general question. Is the tapped hole in your carb spacer plugged? It appears from the photo it is open which would be one hell of a vacuum leak.
It's closed inside, you just can't see it. Thanks.
From: At my Bar drinking and wrenching in Lafayette Colorado
Popping in the exhaust (aka, "afterfire") and hesitation off idle are both indicators of a lean condition. Check, verify and correctly set the timing first (and verify the vacuum advance is functional), and then richen it up.
Full manifold vacuum is the same weather the connection is where you have circled or from below the carburetor throttle blades. Frank's suggestion to show a picture of the distributor vacuum advance hose connection at the carburetor should help clear things up.
If it's not hard to do try it without the spacer under the carburetor first, if it needs more fuel post the carburetor model number and someone may have the specs.
Do you have good transfer slot showing at idle speed.
On a possible lean condition...........................
Sometimes, on an AFB, people use the wrong carb base gasket and the gasket doesn't cover all of the hot slot in the manifold. You could check this by shooting some propane around the base of your carb and space plate and see if the engine speed changes.
even if you take vacuum from the carb, it could be full vacuum (as opposed to ported vacuum) depending on where you hook it up. I always use full vacuum, and most would recommend that for good idle.
On my Holley 4160 it required many parameters to be aligned for smooth performance: timing, distributor springs, vacuum can type, idle screws, accelerator pump cam, nozzle, jets...
In my (modest) experience, solving a problem is not a 'one thing solves all' type of process. It requires many tweaks to gradually move forward. Where I live there is little knowledge about these carbs so I had to learn it myself. In the US there is plenty, but still worth trying to find a really experienced and knowledgeable mechanic. The fact that your's recommend to hook it up to the manifold rather than simply to the full vacuum nipple on the carb (if available) makes me wonder though...The plastic tie wrap on the vacuum line is not a good idea neither, the interior of the 'wrap' is not a circle and may cause leaks rather than avoid them....
A picture and type of carb could help.
If you're drawing vacuum from below the carb's throttle plates (e.g. the carb's base) that IS full manifold vacuum...you don't show a picture of the carb...
There are 1/2 dozen reasons for your symptoms. Vacuum advance's chief benefit is at cruise - you can plug the vacuum source and drive the car and see if you get the same symptoms...
Frankie, vacuum is something I really don't understand but for the fact that it adjusts the timing while the engine is running. Port vs full vacuum is confusing to me. Timing at idle is currently set at 12 degrees (maybe slightly high?) The tapped hole in the rear of the carb is not open so there was no need to plug it. The port of the carb that currently has the vacuum hose connected does have vacuum if I put my finger on it. Could there be a problem with the weights in the distributor causing the timing to be off and on incorrectly? As for the zip ties, the hose was slightly larger and I wanted to be sure no vacuum was lost there. Thanks.
In brief -- PORTED vacuum is ABOVE the throttle plates so there is NO vacuum assisting the idle since the throttle plates are closed - this is a throwback to emissions days and a contrivance to reduce harmful effects to the atmosphere -- not needed now with all fuel injection motors and it "detuned" engines. Once the throttle plates open up by depressing the gas pedal full manifold vacuum is available.
FULL manifold vacuum gives maximum benefit at idle and cruise and is taken off below the throttle plates -- it results in cooler running/idle, smoother performance, better mileage, etc..
Edelbrocks have a reputation for stubborn idle stumble. I tried one too, but switched to a Holley 4160 soon. With what I learned from tuning the Holley, I believe I could now set up (eventually modify, did drill out some channels...) the Edelbrock equally well. Here is a thread that may give some insights https://www.forcbodiesonly.com/mopar...stumble.26068/. Google 'Edelbrock stumble' and you'll get more than you can read in a week-end
Edelbrocks have a reputation for stubborn idle stumble. I tried one too, but switched to a Holley 4160 soon. With what I learned from tuning the Holley, I believe I could now set up (eventually modify, did drill out some channels...) the Edelbrock equally well. Here is a thread that may give some insights https://www.forcbodiesonly.com/mopar...stumble.26068/. Google 'Edelbrock stumble' and you'll get more than you can read in a week-end
Very interesting article. I'm running a 1406 since my AFB had a warped base and was pouring fuel over the engine. Got the Edelbrock on advise of a friend. Thanks.
I have a similar issue with my Holley. Holley Tech. just emailed me and said, "I think have diagnosed a possible cause for your issue. The pump nozzle size is a 21 on that carb. I think that should be changed to at least a size 28. That is two sizes bigger. Part number for the nozzle is 121-128." Bottom line is the carb isn't providing enough fuel when accelerator pump is trying to do it's job.
Mikey, there is a good article about the operation&tuning of an edelbrock here http://www.telusplanet.net/public/gi...delbrock_1.htm.
The 1406 is jetted/rodded very lean (compared to a 1405, marketed as 'identical' to the 1406 but without choke). I remember I had to set jets and rods like for a 1405 to have my crate 350 run fine. But that may just be my configuration.
If you want to try out something easier first, having the acceleration pump inject more fuel is easy to do yourself. A stumble can mean a lean condition, so this could help. Put the lever as in this picture for maximum fuel. and see how it goes. It's where I had put mine. But again, that 's more trial and error than wisdom. I do carb tuning using a Air/Fuel ratio sensor. Those things don't lie and cover up for my lack of 'gut feel seat in the pants' experience By the way, the smaller hose just above his finger is the manifold vacuum where your distributor advance is supposed to go.
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Last edited by alexandervdr; Jul 3, 2018 at 01:57 PM.
I had an Edelbrock on a car for about 40 minutes. I couldn’t get it off fast enough. It’s a pablum, generic bolt-on, one-size-fit-all, sub-optimal “quick fix”.
Vacuum ?
