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  #31 (permalink)  
Old 03-24-2012, 11:24 AM
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I have a 2400 in mine and it makes traffic lights a lot better. I dont think it changed the idle any however but my cam is fairly mild.

What is your vacuum reading at idle both in park and in gear.
Wen you put it in gear what happens to the timing. if it drops you need to fix this first.

I agree with others that more initial may solve some of your problem.

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  #32 (permalink)  
Old 03-24-2012, 09:05 PM
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Quote:
Originally Posted by 23 tbucket
there is no change at idle if I pull the vacum advance
That may or may not be telling you the vacuum advance can is bad or the advance plate stuck.

You need to connect the vacuum advance to a MANIFOLD vacuum source as I described above in the last three paragraphs. If it's connected to a ported source, there isn't going to be enough vacuum present at idle to work the vacuum advance, so there will be no movement of the advance can's rod or change in the idle speed when you attach/remove the vacuum hose.
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Old 03-24-2012, 11:32 PM
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We then set up the mechanical curve to add about 18-22 degrees, all in by apprx 2800-3000rpm's. The curve must NOT start till just past idle speed. This is extremely important. IF any of the timing from the mechanical advance is coming in at idle speed, it typically falls out when the trans is placed in gear. This can cause dramatic drops in engine rpm's at idle speed, and is almost ALWAYS blamed on the carburetor not working correctly.
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Old 03-25-2012, 07:25 AM
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Did you set the initial timing with a vacuum advance connected to a full vacuum port?

I use a ported vacuum port for my vacuum advance.. You have to make sure it's not a EGR timed port by comparing the vacuum reading to a full vacuum port at off idle..

I find the ported source provides a much more stable idle, only a 50 rpm difference when placed in gear, with absolutely NO change in temperature. Low speed acceleration is more stable and snappy too. Trouble is, most people try an emissions, timed, port and of course the motor runs like hell, so they think people like me are crazy...

I do have a Cliffs custom Quadrajet on my motor, that was originally a Brad Urban build..
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Old 03-28-2012, 06:45 PM
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i went ahead and installed a streetmaster torque converter from hughes and it made a small difference but something else is definitly the colpret, I tried another vacum canister on the distributer and it made no difference, one thing I did notice is the throttle is completly off the idle screw and is still running at 1300 rpms in park any thoughts on this?
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  #36 (permalink)  
Old 03-28-2012, 06:57 PM
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bad vaccum or you need to play with your idle mixture screws. regaurdless of what the manual says.
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  #37 (permalink)  
Old 03-28-2012, 07:01 PM
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I'm gonna get a vacum gauge tomarrow to see what kind of vacum I'm pulling
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  #38 (permalink)  
Old 03-28-2012, 07:08 PM
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Quote:
Originally Posted by 23 tbucket
...one thing I did notice is the throttle is completly off the idle screw and is still running at 1300 rpms in park...
Unless the throttle shaft is bent or the butterflies hitting the throttle plate, linkage bent or etc., it could be the choke fast idle.

Look carefully at the choke and the linkage on the passenger side and see if you can tell where the fast idle cam is at. From there you should be able to see what is wrong. It could be it's sticking from dirt, or what have you or it needs adjusting.

You also may have the curb idle screw backed all the way out and the throttle blades ARE closed, but air is getting into the engine from someplace other than the throttle blades. BG carbs can have a built-in vacuum leak they call the Idle-Eze that can cause the idle to be higher than normal, but it won't cause the throttle to not contact the idle screw.

All I remember you saying about the carb is it has sight plugs for the fuel level. What is it?
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Old 03-28-2012, 07:21 PM
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it a 600cfm, dual feed 4 barrel with electric choke, made by summint racing, part #sum-M08600VS,a nd the distributer was also made by summit racing part #SUM-850001R, it has a 50,000 volt coil, medium weight advance springs
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  #40 (permalink)  
Old 03-28-2012, 07:35 PM
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I believe the choke/fast idle mechanism might just be the problem.

To begin with, the choke has to be fully open or the fast idle could be engaging. If the choke is FULLY open and the idle is still high and the throttle isn't touching the curb idle screw, go to the choke/fast idle cam and take a good, close look.

From the MANUAL:
Quote:
Manual and Electric Chokes
2. If the fast idle RPM is too low or too high for your preferences, SHUT DOWN THE ENGINE! Advance the throttle to wide open, exposing the fast idle set screw below the choke housing (See Figure 8).
3. Using a 1/4" open end wrench, turn the screw clockwise to increase the RPM or counterclockwise to decrease the RPM.
The factory setting should give you a 1500-1600 RPM fast idle speed.
NOTE: All vacuum ports must be plugged to properly adjust the fast idle RPM or it will result in a false setting.
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Old 03-29-2012, 03:29 PM
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( I got the idle screw working) after the new torque converter, I set the idle in park at 800 rpms, then set the timing at 10 degrees advanced with vacum pluged off, when I connected the vacum line it did not advance it at all but I was able to get it tuned down to 1000 rpm in park and 650 in drive (300 rpm less then before) does this seem right or do I still have a problem you think?
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  #42 (permalink)  
Old 05-03-2012, 03:03 AM
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Ive tried the torque converter idea in the past when I was just learning and it didn't do anything for me. Still sounds really not right that the vacuum canister on the distributor is doing nothing. Is your vacuum advance currently hooked to full manifold or ported vacuum? If you can fix up the distributor and remove timing as a variable from the problem, you will be so much farther ahead.

Someone suggested getting the Mighty Vac hand held vacuum pump, and its definitely one of the best tool you will ever own for distributor tuning. I would pull the Distributor out and make sure the advance weights are moving freely and visually verify that the the vacuum canister is moving when you apply vacuum to it with the Mighty Vac tool. The mighty Vac will also have a gauge on it telling you how much vacuum before the vacuum advance is all in. If you are making 15" hg at idle in gear and the can is not all in until 16" you are gonna have major idle problems. If your running vacuum advance and its not set right, when you put the tranny in gear, then engine loads up, the rpm's drop, then vacuum drops so timing drop out, and the whole thing just falls flat one its face.

The vacuum can must be hooked to full manifold and I can post and article written by one of the original GM engineers who developed vacuum advance to back up my theories An adjustable vacuum can will allow you to tune it so it is all in at least 1" below your vacuum reading at in gear idle. If your cam is lumpy, then make sure you can is tuned so it is all in 1" below what seems to be the lowest point the vacuum gauge on the engine fluctuates to at idle. As well Crane cams makes an adjustment plate which allows you to limit the total amount of vacuum advance you can add.

Its really important that you know how much vacuum your engine is producing in gear and tune accordingly. You need to get a really good handle on what your distributor is doing and get is close to where it should be, then you can fine tune your carb a bit, and then take more vacuum readings, and then more fine tuning of the timing, then carb etc. You should of course tune your carb in park, but make sure you know your vacuum readings in gear to tune your vacuum advance properly.

I would set initial timing to 14 degrees, set the total mechanical timing to 20 with the curve starting around 1200 rpm and ending around 3000-3200rpm. you will likely have to pick up a kit with springs and bushings to get the mechanical timing set right.

Have you vacuum advance limited to 10 degrees, hooked to full manifold vacuum tune it so it is all in at least 1" below your idle vacuum reading in gear. I used my Mighty Vac and shortened the slot in the vacuum canister with my welder, and tested it on the motor to get exactly 10 degrees with the timing light. doing it this way means you have to remove the distributor many times though. With the crane kit, is very simple limit your vacuum timing.

Any questions at all, I'm glad to help if I can. You may have carb issues too but sorting out the timing and getting it rock solid is a lot easier than it seems.

My pickup truck makes roughly 470hp and my mother can drive it with one foot all day long so I know whatever I have done works perfectly for me.

Last edited by Scrumgees; 05-03-2012 at 03:24 AM.
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  #43 (permalink)  
Old 05-07-2012, 05:40 PM
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thanks you for the info, im gonna play around with it this weekend.
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  #44 (permalink)  
Old 06-12-2012, 11:17 PM
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Check your battery ground cable bolt. I had same problem.. finally I found out it was loose ground cable.
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  #45 (permalink)  
Old 08-08-2012, 04:23 PM
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Timing doesn't advance when the vacuum canister is connected? That's a bad vacuum canister, wrong vacuum canister, you don't have vacuum at idle which means that you're connected to the wrong port on the carb.


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