Re: Stock Carburetor Jetting
Dale;
Are you still with us?
Sorry to bloviate so much in your thread.
Stu Fox
Dale;
Are you still with us?
Sorry to bloviate so much in your thread.
Stu Fox
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Re: Stock Carburetor Jetting
Yes, I am still here and reading all the materials that have been posted. I have reviewed Duke's article and fond it terrific. I have not yet purchase a new VAC as I have been working to get the carb cleaned and back on the car. I completed that yesterday (OK, I am slow). This has gotten my car back to running fairly decent. It seems to hesitate and wants to stumble until the engine warms up to running temperature. This may be from the VAC and my mismatched cam or I keep fiddling with the chock. Originally, I was thinking that the engine is lean, but from your post my jetting is close to stock. The 16-389 recommended are .069/.060 and I measured mine at .065/.059 & .069/.059. So one metering rod is .001 richer on the non-power side and .004 on one side for the power mode.
Now I will have to check the hot idle compensator. I would like to know the temperature that it should open, if someone does some testing.
By the way at idle @700 rpm, my vacuum is 15 lbs. Also as with most of us I only cruse around and never push the car very hard, likely 3000 rpm is the most it ever sees.
PS. This Friday I am leaving town and will be gone for about 3 weeks. I will get onto my tuning training after I return. I really appreciate all this information and help.Comment
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Re: Stock Carburetor Jetting
Dale;
Are you still running the two different primary metering rods? I would suggest you try to match these as close as you can to stock, and do it as a high priority item. There are a number of carburetor part vendors from which you can order a matched set. One that comes to mind is:
Carbs Unlimited, Inc (www.carburetion.com)
Click on "parts", select "Edelbrock Carter AFB/AVS"
Your idle @700 sounds ok for the cam you have, but I'm not sure about your vacuum reading which, by the way, should expressed as 15"hg (don't wait for Duke to call you out on that again, Ha!).
Stu FoxComment
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Re: Stock Carburetor Jetting
Typical L-79 cam idle behavior is 750 @ 14-15", and the more idle vacuum at that speed the more optimized the "tune". One should always use an accurate test tach to set idle speed/mixture as the in-car tach is not as granular and accurate.
Last week I helped another member get his '65 L-76 with a L-79 cam squared away. The VAC was jammed up against the manifold (yeah, the dist. gear was installed backwards), so maximum initial timing was only 10 and the 24 degree distributor centrifugal didn't even start until 1300! Idle was 750 @ 13.5"
Once squared away with 15 initial, 24 degrees centrifugal that starts at 900 and is all in at 3200, and the idle mixture screws one turn out from the seat, it pulls close to 15" @ 750. The installed 236 16 VAC met spec within reason and since the engine is dressed as the original 365 HP, the decision was to leave it installed rather than go with a 12" B26.
He'll start a thread in a few days to tell the whole story.
So, another vintage Corvette engine dialed in and optimized... only about another 50,000 to go.
DukeComment
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Re: Stock Carburetor Jetting
Stuart, Yes I am still running the 2 different metering rods, but I have been searching and will purchase a matching pair. Per this discussion, I am looking for the 16-389 or equivalent .069/.060 rods. I did search at Carbs Unlimited and couple of other places they don't list any metering rods that match my specifications. The closest they had was .070/.057. It seems the Edelbrock carbs must use different rod and jet sizing.
Thanks for my braian fart, I try to remember its hg. I guess that the sprints for the metering rods don't have 15 pounds of strength--haha backComment
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Re: Stock Carburetor Jetting
I have found a source for the metering rods, The Carburetor Shop in Eldon Missouri, but the price seems high. They want to purchase a kit first for $78, then the rods which thy make to order are $180. They seem like a good group of people and make all their own parts here in the US. http://www.thecarburetorshop.com/
so I am still doing a little more searching before I order from them.Comment
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Re: Stock Carburetor Jetting
Well I have been searching for metering rods a lot today. The closest thing I have found is a .068/.057. Compared to the 16-389 .069/.060 recommended. This would richen the carb .001 at cruse and .003 under power. Should I keep looking or how much would this effect my car? These are at: http://www.carburetor-parts.com/Cart...Rod_p_258.html Should I also order a set of springs for the metering rods, What happens after 50 years of use on the springs?
I should have also informed you that I do run a Petronix Ignitor III ignition set with a high output coil. It seems to me that having a good spark helps keep the plugs firing.
I am picking up the new VAC tomorrow and I will check the end play in the distributor.
I also ordered a battery for my Sears Dwell/Tach meter. Hard to find a 4.5V batter these days. Now I need to find an old distributor machine. We used to play around a lot with the advance curves.
Thanks allComment
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Re: Stock Carburetor Jetting
Dale;
You will probably get some flack about the Pertronics from the purists, but I would only question why you reached out so far for the III unit. The II unit is what I use because I want my coil under the shielding, and I also didn't think the extra features were worth more money for me, specially the rev limiter. That may be something I should have with my 63 L-76 to save my rods, but any engine that already lives below 5500 rpm should not need that.
You say you are going to check your distributor's end play - I'm surprised you did not do this already when you installed the Pertronics to set the gap.
Sounds like you're making progress though. Keep at it, specially with the metering rods. The Edelbrock spring kit has at least one set in it that is close to stock, but I've experimented wth the others and found no advantage. Some re-builders just stretch the older stock ones when they put them back in, Ha! You're not needing to " tune trackside", or working with a long duration racing cam.
Stu FoxComment
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Re: Stock Carburetor Jetting
The fuel flow area on the primary side is the area of the jet minus the area of the rod. The difference between the .068 rod and .069 is only about 2.4 percent richer. You can do the math for the power step. Those rods should be okay.
I'm not sure how to ID the metering rod piston springs, but check that they are the same. I think the most common puts the rod on the power step at about 5" Hg manifold vacuum.
As far as the spark advance map is concerned, just buy the Mr. Gasket 928G spring kit and install the gold or silver springs. It's tough to find a distributor test machine nowadays, but a dial back timing light is really all you need to determine the curve on the engine.
You want the most aggressive detonation-free centrifugal curve you can achieve with available springs, but the choices are limited, and I'm not aware of anyone who got into detonation using the springs in this kit. Most engines have actual comparession ratios significantly lower than what owners and "engine builders" think because of the use of thick head gasket and not taking the requisite measurements during rebuilding to compute the actual CR.
The Federal Mogul parts catalog is online and they may still have some AFB/AVS rods available.
DukeComment
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Re: Stock Carburetor Jetting
Stuart, I only went with the Pertronics III because I got a great deal o it. I am using it with the Flame-Thrower III the low resistance 0.32 ohm coil which does fit under the distributor shielding. I sure don't use all the options, but I went stupid one day and left my key on and burned up my previous Pertronics, so this one is protected and does have multi-spark. I just like to hae good spark to keep the plugs clean since I just putt around most of the time. My distributor was rebuilt by someone when the frame-off restoration was done several years ago. I believed he was a good mechanic, but I have gotten to the point of not trusting hardly anyone, even myself. I have just gone through seveal fuel pumps, the after-market ones seem to be bad. I now have one rebuilt by "Fuel Pumps A2Z" and I believe I have that fixed. They seem to be really good.
You have really been helpful, ThanksComment
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Re: Stock Carburetor Jetting
Dale;
I should clarify; when the Pertronics III first came out, their Flamethrower III coil was not shaped like a standard coil and would not fit under the shielding. That is why I was not interested in it. Their latest version does. BTW, the box for the new III coil says it can be used with a II sensor unit, but the directions inside says that it can not. We called their tech people and confirmed that their box is incorrect. Vendors that carry them got fooled too and have had to take a lot of III coils back. That might be why you got a good deal. As for your noting that you went to the Electronic Ignition for better spark plug life, well, I did it to save my knuckles and to ensure I could transition from stop and go street driving to redline on an on ramp!
Take note of Duke's last post in which he addresses your metering rod dilemma. If you can get close to the same fuel flow area with rods from a source that is reasonable, then that's your best bet. The Carburetor Shop in Eldon, MO. are one of the best sources, but they do want a good buck for their stuff. They used to catalog a lot of service tools for Carter rebuild shops too, but as their stock runs out they don't carry any more. They are, however; very knowledgeable people and have written a lot of good service information.
Stu FoxComment
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Re: Stock Carburetor Jetting
FYI - I am leaving tomorrow morning and will be gone about 3 weeks. Wen I return I will have the new metering rods, VAC and will get ready to finish tunning my car. Thanks to all who helped out and looking forward to when I return to complete the task.Comment
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Re: Stock Carburetor Jetting
Dale;
Have a good trip. When you get back, if the new metering rods don't work out the way you want, I might be able to help you out. I find I have 3 sets of 16-389's and only 2 carburetors I use them in. My third carb is a doner.
Stu FoxComment
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