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Why wont the secondaries open on a holley 4150

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Jim_66SS

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66 Chevelle SS396 & 66 Chevelle 327 Convertible.
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Discussion starter · #1 ·
The secondaries on a friends holley 2818-1, which is on a 74 327 with a 65 3844461 aluminum intake, won't open? We did the thing where you tie a twistie to the shaft and see if it gets distorted, it doesn't This carb and intake was used on the 65 corvette with the 327/350hp.

We did the suck test on the diaphram and the shaft will suck up and hold. Don't know what cam he has in there. Appears that the original spring is in the diaphram. Also make sure the gasket seal was good between the diaphram and the main body.

Would there be a problem with not enought vacumn? We did manual connect the secondaries and the car preformed a lot better. Thanks.
 
#2 ·
You can try a lighter spring in the diaphram to see if that makes a difference.
Was there still a ball bearing in the diaphram housing still?
Sometimes I leave them out to allow the secondary's to kick in or open better.
Its not really vacuum that opens the secondary's, its venturi action passing through the main body that opens them.

Dave
 
#5 ·
Are you doing this test with the car stationary or under load?
They will NOT open If the car is in the driveway.
 
#8 ·
His biggest problem is that he doesn´t have a doublepumper. I got tired of getting old and grumpy waiting for my secondaries to kick in. I`m only 32.
Got a double pumper, never been happier.
 
Discussion starter · #10 ·
JC396 said:
I've never seen one that would open correctly...always used a machine screw, nut and washer in the secondary slot to "mechanically" pull them open...back in the day.
Click to expand...
We did that and the car really had some zip. But with letting the diaphram do the work they won't open.

Did the twister test on my stock 396 with 3419 holley and it feels and appears the secondaries are working OK.
 
Discussion starter · #11 ·
Dave427 said:
You can try a lighter spring in the diaphram to see if that makes a difference.
Was there still a ball bearing in the diaphram housing still?
Sometimes I leave them out to allow the secondary's to kick in or open better.
Its not really vacuum that opens the secondary's, its venturi action passing through the main body that opens them.

Dave
Click to expand...
Think we should try to remove that ball and see what happens.
 
#12 ·
Removing the ball causes the secondaries to slam open and are used in conjunction with the spring to regulate the opening rate preventing a bog from too low a booster signal.The carb on my truck needed some secondary tuning and I found this secondary diaphram that works perfect because all I have to do is turn a screw and test drive it.
http://www.summitracing.com/parts/PRO-67235/
 
#13 ·
Everytime I have removed the checkball I never had an issue with a bog.
We did some back to back testing at the track a few years back on a 454 and didnt pick up or lose any 60 ft, ET or MPH...but I guess the spring that was in there (short yellow) worked well.
 
Discussion starter · #15 ·
update. Still can't get the secondaries to open. Did the suck test, so diaphragm should be good. Made sure the gasket between main body and diaphragm housing is good. Correct shaft length. This is a 1979 Holley 2818-1 with vacuum port for vacuum canister on the metering block. That little ball that is suppose to be in the diaphragm is missing.

Secondaries open when we manualy hook them up to the main throttle shaft. We bought a Holley quck change kit. We used the lightest spring and they will not open. Throttle shaft and free and does not stick or hang up on anything we can detrmine.

This is on a 73 350 engine with a 65 covette intake. We don't know the cam shaft.

Thanks.
 
Discussion starter · #16 ·
von said:
If you find the tiny orifice in the primary venturi, you can blow compressed air across it and the secondaries will open if everything is correct. It's much easier to do with the carb off the car.
Click to expand...

Von, where is tha orifice located.
 
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Jim_66SS
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