School me
- Thread starter Cobain03
- Start date
Like Bottlefed70 stated, if you pulled them open with the engine running and it didn't bog down, the fuel is flowing. No more than you can open the primaries without over revving it in neutral with no load, you can only crack the secondaries slightly and the amount of fuel they draw will not be visable. Work the throttle with the engine off, and see where, on the driver's side linkage on the carb, connecting the two sides together you can insert a machine screw and nut to convert it to mechanical operation. Do this and then drive the car, you will be guaranteed to have full secondary operation and then you will be able to "feel" if they were opening on their own without the screw. The only other way to see if they're opening is to remove the hood and drive it without the aircleaner and get a freind to watch the secondary linkage and see if they're opening. That or do it on a chassis dyno.Cobain03 said:
I just swapped out my vacuum secondary spring a few minutes ago.. it was the black one, which according to the chart doesnt BEGIN to open past 4k rpm, and never fully opens. I put in the yellow spring, which begins to open around 1500, and fully opens a little past 5k i beleive. WOT, no stumbles.... I am going to try the short yellow spring later on.
Black spring FTL.
Black spring FTL.
Negative, the vacuum secondary spring kit came with a manual and a chart. It estimated on a 350CI engine, at what RPM @ WOT the spring would begin opening, and also when it would fully open. It also had a chart for a 454 CI engine. I derived the approximate RPM's for a 289 engine with that info.
I should have added that the RPM's were approximated @ WOT, with the airflow and efficiency of the engines in the chart estimated at stock/normal values. The chart came in a kit for 4160 Holley carbs.
Also, vacuum source for the secondary diaphram... I am unsure if it is manifold vacuum, or ported... or perhaps some special vacuum source. The manual was very specific in adding that there were ball bearings in some model carbs secondary diaphram ports that should not be removed because they served some special purpose. I'll scan the manual later tonight if you would like
I should have added that the RPM's were approximated @ WOT, with the airflow and efficiency of the engines in the chart estimated at stock/normal values. The chart came in a kit for 4160 Holley carbs.
Also, vacuum source for the secondary diaphram... I am unsure if it is manifold vacuum, or ported... or perhaps some special vacuum source. The manual was very specific in adding that there were ball bearings in some model carbs secondary diaphram ports that should not be removed because they served some special purpose. I'll scan the manual later tonight if you would like
ok here it goes vacuum secondaries 101.
lets start out with the pod. it is a vacuum diagphram with a mechanical linkage. on the top side of the diagphram there is a spring(this is also the vacuum chamber)opposite of the linkage. at rest the pod pushes the linkage out closing the throttle plates. when vacuum is applied the diagphram pulls on the linkage and compresses the spring.
next is the vacuum source for opening the secondaries. IT IS NOT MANIFOLD VACUUM. it has its own special port on the underside of the venturi. which basically utilizes bournoullis principal, air moving over a curved surface creates vacuum- more flow more vacuum(same damn thing as main metering system). so more cfm means more vacuum.
add that vacuum to the pod and you have vacuum secondaries. so the more cfm thru the primaries the more the secondaries open. put in a lighter spring and it happens earlier.
lets start out with the pod. it is a vacuum diagphram with a mechanical linkage. on the top side of the diagphram there is a spring(this is also the vacuum chamber)opposite of the linkage. at rest the pod pushes the linkage out closing the throttle plates. when vacuum is applied the diagphram pulls on the linkage and compresses the spring.
next is the vacuum source for opening the secondaries. IT IS NOT MANIFOLD VACUUM. it has its own special port on the underside of the venturi. which basically utilizes bournoullis principal, air moving over a curved surface creates vacuum- more flow more vacuum(same damn thing as main metering system). so more cfm means more vacuum.
add that vacuum to the pod and you have vacuum secondaries. so the more cfm thru the primaries the more the secondaries open. put in a lighter spring and it happens earlier.
Have one on me. 
so.. more airflow = more cfm = more vaccum right?
airfilter vs no airfilter on a carb. your getting a whole lot more air which is more vaccum. that would screw things up wouldnt it?
airfilter vs no airfilter on a carb. your getting a whole lot more air which is more vaccum. that would screw things up wouldnt it?
Cobain, look at the secondary vacuum diaphragm. See the straight up and down rod that comes out of the bottom of it? Now, with the car off, open the vacuum secondaries manually, and note how you can move that rod up and down. OK, now you have seen how the rod works when the secondaries are applied.
Now, look at the carb with the car off and note the position of the rod. This is the position of the rod with the secondaries closed. As you have seen by playing with the linkage, when the secondaries open, this rod will move upward to facilitate that.
Place a paper clip at the very top of the rod with the car off. By looking at the assembly, can you see what will happen when the secondaries open and the rod moves upwards? When the rod moves upwards, it should force the clip to slide down the rod. When the secondaries return to the closed position, the rod will move back down, taking the paper clip with it.
If your secondaries are working, the clip should have moved down the rod and be resting at the bottom. I may try and take pictures this weekend and post them if you are still fuzzy.
Now, look at the carb with the car off and note the position of the rod. This is the position of the rod with the secondaries closed. As you have seen by playing with the linkage, when the secondaries open, this rod will move upward to facilitate that.
Place a paper clip at the very top of the rod with the car off. By looking at the assembly, can you see what will happen when the secondaries open and the rod moves upwards? When the rod moves upwards, it should force the clip to slide down the rod. When the secondaries return to the closed position, the rod will move back down, taking the paper clip with it.
If your secondaries are working, the clip should have moved down the rod and be resting at the bottom. I may try and take pictures this weekend and post them if you are still fuzzy.
geostang351
Member
geostang351
Member
Sorry dude. It just helps. There are two things I don't know: Tranny's and carbs, so this is a big time learning experience.
All I know is my Edelbrock carb sits under my airfilter and a small screw turned clockwise or counter clockwise effects my engines RPM's at idle
All I know is my Edelbrock carb sits under my airfilter and a small screw turned clockwise or counter clockwise effects my engines RPM's at idle
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