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Thread: Tuning and Vacuum Advance

  1. #1
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    Tuning and Vacuum Advance

    I've gotten my 63 Hawk road worthy after too many years of sitting in the garage. During the process I rebuilt the Carter AFB carburetor (3540S). Now I'm just fine tuning things for best performance. The plugs were black, so I changed metering rods to lean the mixture. I'm running .093 main jets and metering rods with .075 idle step and .047 secondary step. (I'm in Colorado about 5200' altitude) Starts and runs GREAT no smoke at idle and but a bit when revved up. Problem is mixture screws have very little effect. Idle speed increases and idles best with screws all the way in. No vacuum leaks that I can find. Sprayed carb cleaner around base of carb and intake manifold. Has 16" of vacuum at idle from the power brake vacuum source on the intake manifold, yet only 10" at the hose going to the vacuum advance canister on the distributor from the carb. So at idle, I'm not getting any vacuum advance. Connected my vacuum pump to the advance unit and it will advance with 15" of vacuum. I've sprayed carb cleaner in the vacuum port on the carb and the engine will stumble while doing it so I don't think the passage is clogged.

    Any ideas as to what the problem is? I'm frankly stumped.

    Also, does anyone know what the diameter of the vibration damper is on a non R series engine?

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    You might find this link interesting. Pete has a great series on a 289 rebuild on Youtube. https://www.youtube.com/watch?v=gANEOu_ADAw
    Jim Kaufman
    Kearney NE

    1952 2R10
    1953 Champion (sold it and still kicking myself)
    1962 GT Hawk
    1963 R3984 Avanti R1

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    The vacuum line that goes to the distributor is ported vacuum. At idle it should be just about 0 and should as the engine speed increases to advance the distributor. The purpose ideal of ported vacuum going to the distributor is to increase the advance at a steady cruise speed to increase the fuel mileage. Once the throttle is opened the advance retards to avoid the dreadful pining.
    There is nothing wrong with your readings.
    The manual says to disconnect and plug the line going to the vacuum advance when you set the timing. Doing this prevents the possibility of a small amount of vacuum advancing the distributor.
    Ron

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    There is a good possibility that you old AFB has some worn or warped parts causing internal leaks. The idle mixture screws when turned all the way in should cause the engine to stumble and stall. The spark advance while important won't cause the symptoms you describe. Bud

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    President Member SScopelli's Avatar
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    Quote Originally Posted by ColoradoHawk View Post
    I've gotten my 63 Hawk road worthy after too many years of sitting in the garage. During the process I rebuilt the Carter AFB carburetor (3540S). Now I'm just fine tuning things for best performance. The plugs were black, so I changed metering rods to lean the mixture. I'm running .093 main jets and metering rods with .075 idle step and .047 secondary step. (I'm in Colorado about 5200' altitude) Starts and runs GREAT no smoke at idle and but a bit when revved up. Problem is mixture screws have very little effect. Idle speed increases and idles best with screws all the way in. No vacuum leaks that I can find. Sprayed carb cleaner around base of carb and intake manifold. Has 16" of vacuum at idle from the power brake vacuum source on the intake manifold, yet only 10" at the hose going to the vacuum advance canister on the distributor from the carb. So at idle, I'm not getting any vacuum advance. Connected my vacuum pump to the advance unit and it will advance with 15" of vacuum. I've sprayed carb cleaner in the vacuum port on the carb and the engine will stumble while doing it so I don't think the passage is clogged.

    Any ideas as to what the problem is? I'm frankly stumped.

    Also, does anyone know what the diameter of the vibration damper is on a non R series engine?

    What RPM is your engine running at Idle, and your timing with the vacuum disconcerted and plugged?

    Since you are on an AFB, your fuel pressure should be less than 4.5 psi, even above 1000 rpm. Anymore and it may cause it to push past the needle seats and flood.

    Your Idle circuit works best with a minimal opening of the primaries. Since you are stating that you have 10" of vacuum on your vacuum advance hose, this tells me your Idle screw is in to far. You really should get 0" on that port at idle.

    if you look at the instruction, it shows using a particular wire thickness (not feeler gauge) to adjust the base primary openings.

    Also, during your rebuild process, did you set the float height correct with the gasket in-place?

    Look in the carburetor. At Idle it should be dry, with no fuel seeping from the ventures.

    My steps would be:

    1. Adjust the intake and exhaust vales, warm as specified.
    2. Close the idle screws and open each of them two full turns.
    3. Start the engine, set RPM to 750 and get the timing around 8 to 10 deg. 4 is OE, but this gas is crap.
    4. Get the RPM back around 750. Hopefully you have 0" on the vac adv port, and no more than 7". Most Studebaker advances start at 9".
    5. The Idle adjust screws should be effective now.

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    Actually, ths AFB has timed vacuum. Ported is a different animal altogether. Regardless, if your idle screws have little effect, it is likely your throttle plate is open too wide. Disconnect and plug the vacuum advance, set the timing at correct idle speed, then reconnect the advance. Hopefully that will help.

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    It does not mater what you call the vacuum going to the distributor. It is not manifold vacuum. At idle it should be almost 0. i missed his saying it was 10 inches. As others have said it sounds like the throttle plates are open too far.
    A standard Studebaker V8 calls for a idle speed of 550 and a R1 650. My AEA tune up sheets call for the idle screws to be open 1/4 to 1 3/4 turns. All I ever did was to turn them in one at a time until the manifold vacuum started to drop and back out a 1/4 of a turn. And repeat the process until the engine run as smooth as possible. All the while keeping the idle speed at what I wanted it to be.
    Ron

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    When I rebuilt the carb, I made absolutely sure the float level and float drop were exactly right on. I checked and double checked to be sure and was extra careful when I put the top back on that I didn't bump or jar them while going in.
    At idle the venturis are dry with no gas seeping in.
    My car is a 4 speed, and I have it idling at 700 rpm, there is no way I can get it to idle at 550 with the cam I have in it.
    The timing was set with the vacuum line plugged and right on the IGN mark on the damper.
    From what I can see looking down the throat of the car at idle, the throttle plates are almost completely closed. Very little space if any between the butterflies and the throat, but I will double check that.
    In the past with this car, as soon as I connected the vacuum line to the distributor after setting the timing there was an audible pop from the vacuum canister as the advance was activated.

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    I've gotten my 63 Hawk road worthy after too many years of sitting in the garage. During the process I rebuilt the Carter AFB carburetor (3540S). Now I'm just fine tuning things for best performance. The plugs were black, so I changed metering rods to lean the mixture. I'm running .093 main jets and metering rods with .075 idle step and .047 secondary step. (I'm in Colorado about 5200' altitude)
    It is to be assumed you drove the car a lot in te past and it presumably ran OK. Why does it now require a jet change?

    there is no way I can get it to idle at 550 with the cam I have in it.
    This would have been good information for previous advisors to have.

    jack vines
    PackardV8

  10. #10
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    With a more agressive cam, you may need more timing.
    My 64 Avanti R1 has Isky ST5 - similar to R2+. I have initial timing set to 8 BTDC instead of 4. Additionally, I have Edelbrock 600 cfm with the vacuum advance on the full port - not timed. The engine runs very strong with no pinging on pump premium here at sea level. The block has been zero decked with .060 flattops and I am using the composition gaskets to maintain a decent quench. With all this, the compression is somewhat above factory.

    BTW, my idle screws behave as expected.

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    Quote Originally Posted by PackardV8 View Post
    It is to be assumed you drove the car a lot in te past and it presumably ran OK. Why does it now require a jet change?
    I changed the metering rods since the plugs were black. And, because I'm older and hopefully wiser now. I was in my mid 20's when I set it up and didn't have the endless info of the internet back then or quite the understanding of things now that I'm 51.

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    President Member SScopelli's Avatar
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    Quote Originally Posted by ColoradoHawk View Post
    I changed the metering rods since the plugs were black. And, because I'm older and hopefully wiser now. I was in my mid 20's when I set it up and didn't have the endless info of the internet back then or quite the understanding of things now that I'm 51.
    On OE AFBs or Edelbrocks, there are three items to change to get fuel ratios correct.. Jets, Rods, and Springs. Since you have a non-stock cam, I would have started with the springs first, since a cam change, changes the vacuum profiles. When you stated "..16" of vacuum at idle," it should have triggered my brain that you did not have a stock cam. That is why I started with step 1 to adjust the valves because stock, I believe is 19" to 23". at idle.

    To properly get correct fuel ratio, you really need some test runs with an O2 sensor setup. I'd go back to OE configuration and then make adjustments based on the test runs.

    Also, the Idle circuit is different from the Run circuit.. Jets, rods or springs have no effect at idle.

    Since you are using a Std dampener, you can use an "Advanced" timing light, set it to 4 deg and bring the IGN back to the pointer for 8 deg.

  13. #13
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    The Studebaker combustion chamber design needs much more ignition timing than the "book" recommends to run well/properly.
    A flat tappet cam change in the Stude world shouldn't require a huge fueling change. And most likely richer...not leaner (for a more radical cam)..! If...everything was assembled properly. Again, more on the ign. timing side.

    Vacuum advance wise, you'll have much less vacuum with a hotter cam. Therefore, the stock canister may/probably will not work. You'll need a low vacuum version, which I do not believe is available for the Stude.
    As noted, either full vacuum or as I do, no vacuum advance. It's all n the distributor adjustment.
    Mike

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    Golden Hawk Member DEEPNHOCK's Avatar
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    Pretty good writeup just showed up in my e-mail this morning.....

    http://www.onallcylinders.com/2017/0...llCylinders%29
    Jeff



    Note: SDC# 070190 (and earlier...)

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    Thanks for the link. I've done a lot of research and reading since I started this post and have come to the conclusion that we SHOULD have vacuum advance at idle. Our cars do not have ported or "timed" vacuum as others have said. That wasn't introduced until the late 70's and into the early 80's to try and reduce emissions, something Studebaker never had to deal with. I replaced my vacuum advance unit that wasn't activating until it saw 15" of vacuum with a unit that starts at 9". I now have it set with 12 deg of base timing and the engine runs so smoothly and idles nicely at 650 rpm now.

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    Sounds like you got it working.
    FWIW, the Avanti shop manual has the vacuum advance beginning between 7-9 inches and all in by 13-15.

    Other models may be different

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    President Member TWChamp's Avatar
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    A good investment to check your vacuum advance is to buy the brass vacuum hand pump and brake bleeder from Harbor Freight.
    Mine was just under $20 with the 20% coupon.

  18. #18
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    Quote Originally Posted by ColoradoHawk View Post
    Thanks for the link. I've done a lot of research and reading since I started this post and have come to the conclusion that we SHOULD have vacuum advance at idle. ....ported or "timed" vacuum as others have saidwasn't introduced until the late 70's and into the early 80's to try and reduce emissions..... and the engine runs so smoothly and idles nicely at 650 rpm now.
    ===============

    Hi Colorado Hawk,

    On line ignition research generally uncovers the detailed posts by former GM process engineer the honorable John Z on various Chevy sites.
    http://www.corvettemuseum.org/learn/...john-hinckley/

    A little while back a poster on one board who knew John Z said he was in the hospital. I have not heard back if John is OK. I wish I'd been able to talk to him.


    His wording often makes ported (non manifold) Vac ADV sound like an invention of the emissions era. i think what he meant, and should have said instead, is that the emissions era made its use nearly universal.

    Post 88 here-
    https://www.jalopyjournal.com/forum/....706544/page-3

    Post 11 here-
    https://www.jalopyjournal.com/forum/...#post-10439588

    --

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    I do have it working perfectly and I think it was the good advice from you, 64studeavanti. Thanks so much. I set the base timing to what you suggested and got a vacuum advance that works exactly like it's supposed to and now the idle mixture screws work like they're supposed to. THANKS!!

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    I don't think i can take credit for your solution, you received good advice from several sources.

    Just to try to clear things up, with every thing stock, there is no timed vs full vacuum issue. There is only one place to connect the va - as the engineers designed it.

    FWIW, once you are off idle there is no difference between timed or full vacuum.

    The issue does arise when there are changes from stock.

    As has been discussed, a more radical cam may need a little more advance. Quite often, advancing the static timing will take care of this. However, if the static timing is advanced too much you risk detonation under load. You can also change the characteristics of the vacuum and centrifugal advances to get everything to work correctly.

    When you change to an Edelbrock, you now have a choice of timed or full vacuum.

    I eyeballed stock stude carbs - stromberg ww, wcfb, afb - with all of them, the vacuum port is partially exposed when the throttle plates are completely closed.

    The timed port on the edelbrock is completely closed when the throttle plates are closed.

    Based on those observations, i believe that there is some vacuum at idle for stock carbs. If it is enough to pull down the diaphram, i do not know.

    I plan on hooking a vacuum gauge to the port on one of my stock setups to measure and will report back.

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