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bikerfox 
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Joined: Aug/02/2009 Location: USA Status: Offline Points: 4465 |
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 Posted: Feb/02/2023 at 12:11am |
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i r and r-ed the engine last week to fix an rear rtv leak in the cross ram.
otherwise, the intake was correctly rtv-ed and affixed to the block, so no vacuum leaks there....the only other area of leakage is the pcv valve that inserts into the valve cover and hoses that insert back into the carbs. i don't believe any leaks there either.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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FSJunkie
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Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
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Posted: Feb/02/2023 at 1:31am |
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Exposure of the idle transfer slots should not cause an erratic idle if the idle air bleeds are sized correctly.
I set Holleys by closing the secondary throttle plates all the way until they jam tight in their bores, then opening them up until they are just barely free. Jammed tight is not good because then the secondary diaphragm cannot pull them open. Basically I have them set as closed as possible without jamming. Then I do all my idle speed adjustment with the primary throttles. Never had a problem doing that. My engines with Holleys happily idle at 500 RPM. Performance camshafts tend to require a wider throttle opening to produce something that resembles an idle, and I will sometimes open the secondary throttles wider in that case if I feel the primary throttles are already far enough. However, I have often found that doing that tends to produce a rougher idle than running on just the primary throttles, because the idle circuit on the secondary side tends to be more primitive. Surging idle speeds in my experience tend to be caused by the distributor vacuum advance being hooked to manifold vacuum rather than ported vacuum, and the engine possessing insufficient vacuum to fully advance the timing at idle. Any change in vacuum causes a change in timing, which causes a change in vacuum, and....you get the picture. A different vacuum advance unit or switching to ported vacuum solves it. |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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bikerfox
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Posted: Feb/02/2023 at 1:42am |
matt--these carbs use mechanical secondaries and there's no vacuum advance hooked up.....
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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Sonic Silver
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Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7949 |
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Posted: Feb/02/2023 at 9:22am |
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He is referring to where the distributor vacuum advance is hooked to, not the secondary operation of the carburetor. You should have a choice of 2 ports to attach it to, one below and one below the throttle plate.
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Sonic Silver
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Posted: Feb/02/2023 at 10:04am |
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At least, I assume that carburetor has 2 places to hook up vacuum advance. I know there is one right above the mixture screw on the passenger side, close to the front float bowl screw in plug. That should be ported vacuum.
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Trader
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Posted: Feb/02/2023 at 10:29am |
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Is this the STR11 intake you still have?
If so, your going to have to adjust idle differently. FSJunkie and Sonic Silver are correct, but the carburetors have to balanced also at idle or they will be out of phase and idle will bounce all over the place. To balance the carburetors for idle, connect a vacuum gauge to each one ported, adjust by turn count to get the engine running, then adjust the idle screws not by RPM or turn count, but vacuum reading. Once vacuum readings are the same, adjust RPM on each little by little, keeping vacuum readings the same. They have to act as one carburetor to have proper idle on a cross ram style intake. Inline, you can use just one carburetor for idle and pretty much close the primary of the second carburetor and it will tune fine.
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Sonic Silver
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Posted: Feb/02/2023 at 10:35am |
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I have zero experience with a cross ram intake, or what it takes to balance the carburetors. I was just referring to the working of the carb itself. I do know how to balance twin SU's on a 240Z for what that is worth.
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bikerfox
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Posted: Feb/02/2023 at 10:57am |
as i said b4, vacuum advance is not hooked up. i don't have one of these (below) hooked up. also, the carbs have been balanced with a dvorak machine, which does the same thing as a vacuum gauge.  |
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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bwamx
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Posted: Feb/02/2023 at 11:47am |
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I'm at work and don't have my carb info here.
I've run a crossram since the 80' on my car with 2 different sets of carbs. Can you give us some more info : Standard or auto , base timing & advance/full , cam info . Do you know the vacuum at idle ? What was the AFR at idle when it was on the dyno if it was recorded ? Most carbs are calibrated for idle as a single not a dual set up . I can say the crossram does not like a lean idle . I tune with an Innovate AFR meter . On the 600 DP's I run now , I'm pretty sure I reduced the idle feed restrictions, along with more air flow at idle. I do have air holes in the throttle blades along with adjustable secondary's from the top. I do run a big long duration cam, but it idles at 800. Bob
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73 Jav-AMX " The Black Widow"
358cu/in Crossram T-10 9" Rear |
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ccowx
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Posted: Feb/02/2023 at 3:05pm |
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When I ran a cross ram, I also had four corner idle, which will likely help your mixture, particularly at idle.
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FSJunkie wrote: