Holley 4150 secondary vacuum

[Jeremy Hedges]

I posted this message earlier this week. So people said that I needed the Diaphram check ball in the secondary diaphram and some people said it would never open with it in. Should I put it in or not?
I have a 65 350hp, the carb has been rebuilt but the secondary will not open?

Thanks

[Clem Z.]

Re: Holley 4150 secondary vacuum

try it without the check ball and if the engine bogs when the secondary opens you need the check ball. some holley carbs have the check ball some do not. with the engine not running open the primary wide open and then make sure you can open the secondary by pushing up on the diaphram rod,you should hear air being pushed out the holes in the venturi. with a check ball you have to turn the carb up side down to do this.

[Clem Z.]

PS

i can usually tell from my holley illustrated parts & specs book if it needs a ball check because they list it in the parts rundown if the the carb used one but john h proved to me that the book is not always correct.

[Everett Ogilvie]

Re: Holley 4150 secondary vacuum

As Clem said, some carbs are designed for the check ball and some are not. If you remove the cover from the secondary vacuum unit and look at the vacuum passage, you can usually tell if your particular carb came with a check ball by looking at the area where it would seat. If there is no groove down in the seat area, the carb did not come with a check ball (and if you put one in on these carbs, no signal will ever reach the vacuum diaphragm). If there is a small groove, the carb originally came with the check ball, and it does not hinder performance to keep it in place. I re-read the Holley book this week and the check ball regulates the OPENING of the secondaries by controlling the signal passing through the groove, so they don't overwhelm the engine as they start to open. The ball will not limit how much they open, so it will not limit wide-open throttle performance. When guys remove the ball, they "feel" the secondaries open, but this is because the secondaries cause a slight bog when they start to open too quickly, and when the hesitation abruptly ends, it "feels" like the secondaries really kick in - this is an illusion - the car is not faster.

The Holley vacuum secondary system is so simple and works so well, there is rarely (never) a need to alter it, if your engine and carb were originally designed for each other. The vacuum secondaries open at a rate, and deliver the flow that the engine requires. As the Holley book says - they "size" the carb to the engine's requirements, meaning you don't have to feather or play with the gas pedal when you nail it. Mechanical secondaries on carbs that are too big for a given engine always bog when you nail it, requiring lots of playing around with the throttle in order to get the engine to get past the bog.

[Clem Z.]

Re: Holley 4150 secondary vacuum

if someone has changed the diaphram housing all bets are off. try it without the ball and it will always open as i posted before.

[Werner R.]

Re: Holley 4150 secondary vacuum

still not sure why you believe that the secondary is not opening. did you try the grease method that clem mentioned?? maybe they are opening just fine and you don't feel it happening. that would be normal. it's if you feel the opening that there might be a problem.
in any event, no-one has mentioned the spring and that has more effect on the opening than a check ball. did someone throw in the very heavy stiff spring??

do you have the quick change housing cover so that you can easily change springs?? if so, how is the rubber gasket?? is it cracked etc??

is the diaphragm good?? they usually tear when you try to remove the cover to change springs. did you test for this??
i suggest you remove the secondary housing and then use a vacuum gun attched to the area where the cork gasket sits. gently apply vacuum and make sure the diaphragm rises all of the wayand stays there]. if this is good and if you used a new cork gasket when originally assembled then either your shaft is tight or the vacuum port that connects the primary venturis to the secondary assembly is plugged. be sure to test for that when you have the secondary housing off. connect a small plastic hose to the port on the body where the cork gasket mates. then [and this is the tricky part] blow cigarette smoke into the tube. you ought to see smoke coming into both primary venturis because that is the route that the vacuum uses to signal the secondaries. if those channels are open and if the secondary shaft is free and if the vacuum test is good and if you have a normal tension silver spring, there is not much else that can go wrong.
let us know if you do any of these tests. finally, how much vacuum does your engine generate??

[Clem Z.]

the spring should be purple *NM*

[John H.]

Re: Holley 4150 secondary vacuum

The engine has to be operating under load, driving the car, in order for the secondaries to open - you can't get them to open just revving it in the garage. The vacuum signal that opens the secondaries has nothing whatsoever to do with manifold vacuum (which drops to zero at wide-open throttle anyway) - its a venturi vacuum signal, generated by high-velocity airflow past a pickup tube in the primary venturi, later assisted by a similar venturi vacuum signal from the secondary venturi once they start to open. Do the grease trick Clem mentioned earlier to confirm whether or not the secondaries are opening; if they're not opening, check the secondary throttle shaft for free movement, the main body vacuum passage and gasket, the integrity of the diaphragm, possible check ball in a non-check ball housing (check-ball housings have four indentation slots around the ball seat to "soften" the onset of the signal), and see which spring is installed.

[Everett Ogilvie]

Re: Holley 4150 secondary vacuum

The guys are right - you can't rev it enough sitting still to open the secondaries. But, I just disassembled the vacuum housing on 3 spare carbs of my own and with the vacuum housing removed from the carb, you can simply suck on the signal opening on the vacuum housing and watch to see if the diaphragm moves, and stays there, as Werner mentioned. This is very easy to do and does not require a vacuum pump (yes, the different springs will change how easily the diaphragm moves, but I have yet to see one I could not move simply by suction). As others have stated, when putting the diaphragm back in place, you have to be very careful - I had to disassemble the cover three times on one of my carbs - turning one of the screws was wrapping up the diaphragm corner causing it to be pulled out of place, which caused a leak. Double check it after you tighten the four cover screws by sucking on it again.

By the way, my spare 3124 had a check ball in place and no apparently grooved seat. I could not make this diaphragm move, so I removed the ball and it then worked fine. Two spare 3247 carbs had the same seat but no check ball, and those units worked fine. I am starting to wonder which carbs did use the check ball. Clem, maybe your book can confirm that 3124 and 3247 don't use the ball?

[Clem Z.]

Re: Holley 4150 secondary vacuum

i will check and post but a trick to use when putting the screws back in to prevent grabbing the diaphram is to put oil on the screw threads.

[Clem Z.]

Re: Holley 4150 secondary vacuum

neither one list the ball check valve.