| ole_Bill | -- 08-02-2011 @ 9:17 PM |
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Is there a step-by-step procedure somewhere for setting up duel carbs using a vacuum gauge?
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| supereal | -- 08-03-2011 @ 6:35 AM |
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Bill: you can set the idle with a vacuum gauge just as you would for a single. Set the idle speed, then adjust the idle bleed needles for the highest vacuum. The main problem with multiple carbs is too much Venturi capacity for the engine vacuum, a problem that isn't adjustable without revising the carb capacity. The usual cure is progressive linkage that doesn't allow the second carb to come on line until the engine speed is high enough to provide adequate vacuum for both.
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| 37RAGTOPMAN | -- 08-03-2011 @ 10:19 AM |
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I would make sure the throttle ROD between the 2 carbs is disconnected for ajusting the 2 carbs, once ajusted, reinstall and adjust the throttle ROD so it does not alter the idle, also make sure both carbs, are all the way closed down to the stops,when ajusting the idle, if open the slightest will effect the idle, your vacuum gauge needle will fall,if the venturi plates are open, its a matter of trial and error hope this helps 37RAGTOPMAN
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| Stroker | -- 08-03-2011 @ 3:32 PM |
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Guys: I kinda hate raining upon your otherwise great advice; but if memory serves me correctly, Ol'Bill has an Edelbrock Super manifold, which has no balance plenum connecting the carbs in the manifold. This complicates things a bit, as the front carb only feeds cyl's 1,2,3 & 5; with the rear carb feeding cyl's 4,6,7 & 8. This was designed as a "wide-open" racing manifold, with very little thought given towards "streetability". So....you basically have 2-4cylinder systems in play here, and changing the settings on one carb only affects the mixture in those cylinders that are connected to it. Progress linkage won't work, unless you want to run on 4 cylinders around town. Disconnecting the linkage between the two will result in the same thing-running on 4-cylinders. The racers really didn't care about "adjusting" for smooth operation, as they most likely were running a cam grind that would preclude anything even distantly approaching smooth operation. About the only thing I can think of that might work is if Bill could find an old "Uni-Syn" system on E-bay. These allowed you to synchronize the airflow through each carb, using a U-tube manometer.
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| 37RAGTOPMAN | -- 08-04-2011 @ 9:16 AM |
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I forgot ,ole-bill has a full race intake, even that UNI-SYN probably will not work, I used these on old VW with twin carbs, you still have lower RPM for them to work, I think tuning the carbs, you have to do by ear, I think it is time for a different intake, one for the street,this might solve a lot of problems, my 3 cents 37RAGTOPMAN Maybe that is why the trans grinds also,because the rpm are to high and not dropping down,so a smooth shift is possible,
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| supereal | -- 08-04-2011 @ 1:42 PM |
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Dan: you have a better memory than me.. If he is running that type of manifold, the mismatch between CFM and demand will be even greater. That is why we recommend using a 350 cfm four barrel carb instead of multiple two barrel types which nearly always have poor low speed characteristics. Coupled with a high overlap cam, idle speed above 1500 rpm makes street use more than a bit tricky, as I recall.
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| Stroker | -- 08-04-2011 @ 2:56 PM |
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Super, et.al. I think Ol'Bill just wanted "The Look" and sound of a 40's style Hot Rod/Dry Lakes/Bonneville/early Nascar motor. I think the cheapest way for Bill to salvage the above requirements; solve his linkage work around, power valve issues and get a reasonable venturi to displacement ratio would be to find a couple of nice old Stromberg 81's (V8-60 carbs), have someone like Vintage Speed rebuild them, and sell his Edelbrock 94's on E-bay. When I put my 300 inch stroker motor from my 32 pickup into my 38 wagon in the early 60's, I had 3-97's on an Edelbrock manifold with straight linkage. This worked ok in the little 32, although I might have well simply wired the throttles open, and driven it with the ignition switch (like a WW1 fighter plane). When I installed it in the heavy 38 wagon, I calmed it down with progressive linkage, and 3-81's. A 4 bbl manifold would have been a much better choice however. Brother Chuck had a stock 8BA in his 51 with a Stromberg A-series carb off a Buick "Fireball" inline 8, on a Edelbrock 4-bbl manifold, and it drove like a stocker.
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| Stroker | -- 08-04-2011 @ 3:48 PM |
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old_Bill" If you would PM me, I'll go into much more detail. I don't want to tie-up a lot of space in this primarily "as Henry built it" Forum with discussions on hopped-up motors. I think I could contribute to your project challenges one-on-one, having "been there". Dan
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| carcrazy | -- 08-04-2011 @ 4:33 PM |
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A kind of a quick and dirty way to adjust multiple carburetors is to: 1) Disconnect the linkage between the two carbs. 2) Close the throttle plates all the way and then just open the throttle plate on each carb a small equal amount (start with about 1/2 turn of each idle speed screw). 3) Gently close all of the idle mixture screws and then open them all an equal amount (start with about 3/4 turn of each). 4) Start the engine and allow it to warm up to operating temperature. 5) Obtain a length of fuel line hose about two or three feet long, place it between your ear and the air horn of each carb and listen to the sound of the air entering each carb with the air cleaners removed. The sound should be the same at each carb - if not readjust idle speed screws to achieve the same sound level. 6) If there is a common plenum chamber beneath both carbs to provide a vacuum source, connect a vacuum gauge to it, and adjust the idle mixture screws to obtain the highest and steadiest vacuum reading. If there is no common plenum chamber, use a tachometer to verify you have achieved the highest and seadiest idle speed. 7) After you are satisfied that the engine is running as smoothly and efficiently as possible, connect the linkage between the two carbs without disturbing the position of either throttle shaft. 8) Once you have the carbs properly tuned and synchronized the acceleration should be smooth and strong. I hope this procedure will help you to get your car running properly.
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| Stroker | -- 08-04-2011 @ 5:19 PM |
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ole: CarCrazy's advice is excellent. Dan
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