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Thread: not enough vacuum

  1. #1
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    not enough vacuum

    after rebuilding the engine in my lark i have a problemo with vacuum. after adjusting the valves three time and numerous timing adjustments i only have 15-16 pounds. i have an r2+ cam and springs and am sure thats not helping. my engine is bored 80 0ver with flat tops but i don't think that has anything to do with the problem. any ide'rs?

    notsoslow64
    1964 lark daytona
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  2. #2
    Golden Hawk Member JDP's Avatar
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    Might be normal with a new engine until everything seats, but make sure the timing is advanced enough too. On a good day, a Avanti engine will only pull 20 inches.

    64 Commander 2 dr.
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  3. #3
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    i advanced the timing as much as possible while watching a vacuum gage, highest it got was 16. i hope you are right though, the engine only has about 200 miles at most. but there is a huge flat spot at low idle. if i try to goose it at all it just dies down. and i am pretty sure its the vacuum issue. thanks guys.

    notsoslow64
    1964 lark daytona
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  4. #4
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    My R2 bored .156 over and R2.5 cam only pulls 15-16 lbs. Runs GREAT. Look for other problems. Check the metering rods. Make sure they are moving freely in their bores. Check the accel pump and squirters, look for a strong spurt not a dribble at the slightest movement of linkage.

    A cam with a little more duration will reduce vacuum at idle. But under acceleration or any movement of the carb plates vacuum will naturally drop down so low vacuum when you goose it is normal and the vacuum at idle reading will not correlate to off idle throttle response.


  5. #5
    Golden Hawk Member Roscomacaw's Avatar
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    Hey! Benny! Good to hear from you again. I've wondered how you were and where you might be. (Benny's a Marine Helicopter tech)

    What sorta carb are you running on this thing?

    Miscreant adrift in
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    1958 Provincial wagon
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  6. #6
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    Not trying to sound like a know it all, but vacuum is measured in inches (of mercury) and not pounds. Old time vacuum gauges (including the one my dad made himself) basically consisted of a vertical tube with a hose attached to the top and at the bottom was a reservior containing mercury. This whole affair was attached to a flat piece graduated in inches. Attach a vacuum source to the end of the hose and it would lift the mercury up the tube where you'd note the inch reading. In the good old days (not really that long ago) high dollar motorcycle carb synchronizers had four of the tubes side by side while the cheapo jobs (like mine) consist or four gauges. Mercury being a no-no anymore, I doubt you can get the mercury ones anymore. Oh, water won't take the place of mercury because it's not heavy enough. I tried that when I was a kid and sucking a big tube of water into the carb kills the engine in a hurry.

  7. #7
    Golden Hawk Member Roscomacaw's Avatar
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    John,

    Fresh outta the service, I got a job at Continental Motors Division of Teledyne-Ryan. I had a job of building up jet eninge/turbocharger test cell control panels and running required cables and tubes to the cells from the control rooms.
    The control room walls were one huge expanse of calibrated mercury tubes that they'd connect various test points to. The "techs" were forever spilling mercury out of the manometers and as a result there'd be big puddles of it in the area behind the manometer wall.[}] Once it was on the floor, it was considered "dirty" - it having been contaminated with dust and debris. The engineers considered the puddles a nuisance and so they were all too happy to let me scoop up and claim whatever was lying on the floors.
    I'd get a quart bottle of the stuff and take it to a scrap metal yard there in Toledo. I usually got about $30 bucks for a quart! A nice little windfall in 1967!

    Miscreant adrift in
    the BerStuda Triangle


    1957 Transtar 1/2ton
    1960 Larkvertible V8
    1958 Provincial wagon
    1953 Commander coupe


  8. #8
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    Benny,
    Your vacuum sounds like it is in the ballpark to me. My R2 bored .060 only pulls about 14 at idle. I'd suggest that the bogging down problem is due to the accelerator pump or a timing/distributor issue.

    Tim K.
    '64 R2 GT Hawk

  9. #9
    Golden Hawk Member JDP's Avatar
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    One issue I've had with the Avanti carb is the metering rod springs. The Avanti engine does not pull enough vacuum to overcome the stiffer springs that are often installed and that allows the mixture to richen too early.

    64 Commander 2 dr.
    64 GT Hawk R2 clone
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    59 3E truck
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  10. #10
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    Good point, John. I use the lightest springs in the kit, the blue ones.

    Tim K.
    '64 R2 GT Hawk

  11. #11
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    If you have the lash set at .010/.012", try loosening them up to .020" and if it is still quiet enough for you (will have slight lifter clatter) that should help the idle some but the 15/16 inches is probably not too far off for the R 1 and 2.

    Ted

    quote:Originally posted by benny_64

    after rebuilding the engine in my lark i have a problemo with vacuum. after adjusting the valves three time and numerous timing adjustments i only have 15-16 pounds. i have an r2+ cam and springs and am sure thats not helping. my engine is bored 80 0ver with flat tops but i don't think that has anything to do with the problem. any ide'rs?

    notsoslow64
    1964 lark daytona
    bd_marks@yahoo.com

  12. #12
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    Hey Ted (and others),
    I'm confused (of course, for me that ain't exactly hard to do). What manner of Stude engine are we talking about here? Lash set at .010"/.012", or even .020"? That is a wee bit TIGHT, or do I misread here--this sounds like a serious thread here and it's not April 1st yet. So what gives? If Benny has an R2 it must be a 289 (and more) and not a F**d engine, so what gives with this valve adjustment advice?

    wagone and the OLD R2 Avanti

  13. #13
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    well i dont think the problem is in the timing or distributor. i've advanced and retarded it into just about every position possible. i put a pertronix setup in it, so i guess points are ruled out. i am running a edelbrock carb, 600 cfm, i know i know its a bit over carbed but when i go through all the symptoms it seems like its not getting enough fuel. i went through the carb before putting it in and cleaned every spec of grime. i didn't replace the excelorater pump though. i will check it for healthy spurt and go from there. thanks a lot guys.

    notsoslow64
    1964 lark daytona
    bd_marks@yahoo.com

  14. #14
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    Which Edelbrock do you have? 1406 with the electric choke or the 1405 manual choke? Or, a 1405 with the electric choke installed. If you have a 1405, you may be dumping too much fuel when the car transitions from cruise to accel. They have larger jets and smaller rods. Is it new?
    ErnieR


  15. #15
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    not new, it is a manual choke. i checked the carb and i am getting a pretty weak spurt from the jets, i am going to change the accelerator pump and see what happens. thanks again guys.

    notsoslow64
    1964 lark daytona
    bd_marks@yahoo.com

  16. #16
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    That will definitely cause a stumble. Check the jets and rods. If they haven't been changed you might be runnung very rich. The manual choke 600's from Edelbrock have .100 primarary jets and 70/47 rods.

    In my R2 I run the .98 jet and 73/47 rods. I had 100's in it and it was too rich.

    ErnieR


  17. #17
    Golden Hawk Member JDP's Avatar
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    The stock Edlebrock metering rods spring are too stiff.

    64 Commander 2 dr.
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    63 R2 4 speed GT Hawk
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    63 Daytona convert
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  18. #18
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    Just saw this - am having similar vacuum readings on my 53 Commander w/289 in it. Have R1/R2 cam, Pertronix module & coil in early Delco, & Edelbrock 1406 (elec choke 600), & dual exhaust w/stock manifolds. I've been struggling with low vaccum as well 13-15 "hg with associated rough idle. More annoying is the part-throttle surge I've got - almost lean surge, almost misfire - hard to tell. Been swapping jets, rods, & springs - keep going back to 1 step leaner - combo 5 on the 1406 chart (I live at 7000', but work at 5300').

    When I get on it, it runs strong, no surge, no miss, no nothing - pulls hard. May be some more tuning in the springs/jets/rods for perfect performance, but until I get the part-throttle surge cured, I'm happy with the setup as-is.

    Tried chasing manifold vacuum leak - sprayed carb cleaner all around, then tried ether - no changes. Tweaked timing & idle mixture and best I can get is 13-15"hg...

    Daddy always said, if yer gonna be dumb, you gotta be tough & I'm one tough sumbitch!

  19. #19
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    Have you tried changing the springs on the metering jets to a lighter pair? It could be that the rods aren't dropping into the economy setting soon enough. I'd also give the distributor a good looking over. If it hasn't been reconditioned, this could be your problem. Driving in thin air presents some challenges.

    Tim K.
    '64 R2 GT Hawk

  20. #20
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    I tried all the springs - lightest to heaviest. No difference in the surging. If I really go overly rich, it will quit surging - which doesn't make much sense to me - especially at my altitude. Like I said, I keep going back to my zero-reference point - 1 step leaner (which is 2 steps leaner than a 1405).

    Pulled the distributor, had it apart, cleaned the advance mechanism well, re-lubed everything appropriately. Bushings seemed tight, so I called it good. Checked my vacuum advance unit with a mity-vac & a "T" to my vacuum gauge - no leaks there either.

    I'm more of a Holley guy than an Edelbrock guy & I do have a fresh 1850 (600 vac) & the adapter to put it on the Stude - so that may go on simply to rule out the carb...

    It's fine as long as I'm accelerating! Which is fine with me, but Johnny Law don't like it much!

    Daddy always said, if yer gonna be dumb, you gotta be tough & I'm one tough sumbitch!

  21. #21
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    Heavier springs could be the answer. The springs push up on the rods to move them up out of idle mode. Vacuum holds them down, this way the fat part is in the jet leaning it out. When you depress the throttle vacuum drops and the rods are pushed up by the springs. Light springs are for cars with big cams so they don't run too rich at idle because the rods are up too high due to springs overcoming low vacuum. I don't think 13-15 is partcularly low, that's where my R2 runs all the time. Part throttle surge is a lean condition but if everything else is satisfactory go with the heaviest spring and work down.

    Also, I used to get a surge because the vacuum advance was pulling the timing too far advance at cruise. I could duplicate the condition by bringing the car up to about 3,000 rpm and listening for a slight miss. That same miss is the surge.

    ErnieR


  22. #22
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    What was your solution? Less initial timing? Or did you fashion some sort of advance stop?


    Daddy always said, if yer gonna be dumb, you gotta be tough & I'm one tough sumbitch!

  23. #23
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    Before the car went "under the knife" I disconnected the vacuum advance. I switched to a Delco window distributor with a Pertronix because I knew I could tune it. The adjustable aftermarket vacuum cans have both a limiter and an internal adjustment for the rate at which the advance comes on.

    So, if I read your post correctly you are running a .095 jet with a 71X47 Rod?

    ErnieR


  24. #24
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    quote:Originally posted by wagone

    Hey Ted (and others),
    I'm confused (of course, for me that ain't exactly hard to do). What manner of Stude engine are we talking about here? Lash set at .010"/.012", or even .020"? That is a wee bit TIGHT, or do I misread here--this sounds like a serious thread here and it's not April 1st yet. So what gives? If Benny has an R2 it must be a 289 (and more) and not a F**d engine, so what gives with this valve adjustment advice?

    wagone and the OLD R2 Avanti
    Sorry I'm so late in answering but I just saw this post. The reason I mentioned the .010" valve setting is he indicated he had the R 2+ cam. That is a reground stock cam and the grinder has a different "ramp" that allows a tighter setting. As I mentioned, this cam can be set as tight as .010" but if you go more than .020" the clatter may be a little noisy.

    Ted

  25. #25
    Silver Hawk Member N8N's Avatar
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    Ernie,

    Just curious, where do you get an adjustable vacuum advance for a Prestolite? I have looked but have not found. I would have ASSumed that MoPar Performance would sell one, but no dice.

    edit: just reread your post and saw that you said you'd switched to a Delco... never mind. But if anyone knows the answer please let me know.

    thanks,

    nate

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  26. #26
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    Nate, I have purchased two Mopar Performance distributors and they both had ( I still have one in my 72 Duster ) adjustable vacuum advances! I might even have one...I'll take a look tomorrow.

    ErnieR


  27. #27
    Silver Hawk Member N8N's Avatar
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    I think you'd need a B/RB vacuum advance for a Studebaker, otherwise you'd have a vacuum retard! or are they the same and you just flip them upside down?

    Actually the dist. in my car is from Dave T. - I bought it at a swap meet not from Dave directly though. Anyone know if he used adjustable advances, and if so how to adjust? I think I'm to the point where I'm going to have to start tuning soon (driveshaft should be here TOMORROW...)

    nate

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  28. #28
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    There is an Allen head adustment screw inside accessed through the hose nipple. The adjustment that can be made through the can is how quickly it reacts to the vacuum signal. The amount of advance is controlled externally with a little "spacer" that manually advances the breaker plate limiting it's travel. You would re-adjust static timing to compensate for the breaker plate change. So, if the amount of advance is the problem you don't need a special vacuum can.

    I think the cans are the same big and small block. My extra would be a big block though.

    Ernie R


  29. #29
    Silver Hawk Member N8N's Avatar
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    Let me get back to the car and see if there's something for an allen wrench to fit into before you start looking, but thanks for the info.

    nate

    (big block Duster? Sounds like fun to me...)

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  30. #30
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    The big block was a 65 Monaco, Duster is a little 318 that I've been promising to finish for my wife. 72 Duster has sentimental meaning to her...to me it's a little boring and that's why I'm having trouble finishing it.

    ErnieR


  31. #31
    Silver Hawk Member N8N's Avatar
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    ISTR that my mixing and matching parts from later cars, you can get big disc brakes on an A-body and HD torsion bars and leaf springs are available... that could make it a little more exciting (so would a 340, for that matter, but we're getting OT here...)

    nate

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