3310-1 vacuum secondary check ball?

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rfoll
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3310-1 vacuum secondary check ball?

Post by rfoll »

I'm helping someone with one of the 780 cfm 3310 carbs. It's in nice shape, but someone screwed up the vacuum diaphragm installation. Huge air leak and inoperative secondary. I noticed the check ball was missing. I have them available, but I know they will work without. I believe the secondary opens much faster. The engine in question is a very well built 383 in a 66 Malibu. I would like to be able to make a good guess at a spring choice with or without the check ball. Any opinions besides just dropping a check ball back in? Thanks, Rick.
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Re: 3310-1 vacuum secondary check ball?

Post by mag2555 »

I am going to assume 3700 lb, but what rear gears ?
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Re: 3310-1 vacuum secondary check ball?

Post by rfoll »

Don't know for sure, but likely 3.73. i saw the build sheet and the motor has all of the big boy parts. The headers are at least 2" primary and the intake is a super victor. Professionally ported heads. It has a hydraulic roller cam with nearly 600 lift. It was dynoed at 506 hp. The headers and intake seem too big for a street car. The current carb is a Holley 83670, way small for that kind of power. I'm thinking to start out with stock jetting and power valves, although i'm inclined to bump the rear jets from 76 to 78. I suspect this is going to blow the tires off at will, so maybe a conservative secondary spring is in order.
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Re: 3310-1 vacuum secondary check ball?

Post by Dragsinger »

A good option is the kit by Holley that allows changing the secondary opening spring by only removing the top cap, thus, the diaphragm does not have to be disturbed. That kit plus an assortment of springs will make it easy to find the opening rate sweet spot.
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Re: 3310-1 vacuum secondary check ball?

Post by Tuner »

The original 3310 spring works good if you increase the coil diameter of the coils between the bottom coil which must seat in the diaphragm and the small coil that latches to the lid. Progressively expand the intermediate coils to close to the OD of the bottom coil.

I like to use the ball and drill a .035" hole from the ball seat to the passage below the seat. Drill parallel to the throttle shaft at an angle that puts the drill point in the bottom of the check ball seat against the vertical wall at the intersection of the vertical wall and horizontal seat for the ball, and the flutes of the drill bit near the top of the hole 180 deg. across. That will be near a 45 degree angle down and toward the gasket flange to the carb body. I put the drill bit in a pin vice and the pin vice in a hand drill motor. Lube the git with nose grease and use a delicate touch.

The long yellow spring is a good choice, but enlarging coils of the original spring reduces the spring rate and quickens the opening and provides good WOT opening.

No spring will work if the booster nipple in the passage to the vacuum servo is not in the primary venturi. I think the 3310-1 all had the nipple but be sure it is in the one you have.
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Re: 3310-1 vacuum secondary check ball?

Post by rfoll »

Dragsinger wrote: Wed May 24, 2023 9:24 pm A good option is the kit by Holley that allows changing the secondary opening spring by only removing the top cap, thus, the diaphragm does not have to be disturbed. That kit plus an assortment of springs will make it easy to find the opening rate sweet spot.
I have the cover and spring kit.
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Re: 3310-1 vacuum secondary check ball?

Post by rfoll »

I think I will leave the ball out or look through my pile for one with the pressed in orifice. Maybe start out with the purple spring.
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Re: 3310-1 vacuum secondary check ball?

Post by F-BIRD'88 »

It won't matter which spring until that booster pipe extension is fixed.
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Re: 3310-1 vacuum secondary check ball?

Post by 1980RS »

Here's what you do, throw the crappy Holley cover in the trash and get a QF adjustable cover. Stick a purple spring in the pod and then go out and make some test runs adjusting the screw in the cover. I did not know how well they worked until I had one on my FST 850 VS carb and was able to dial that carb in perfectly, no bogs, no sags.
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Re: 3310-1 vacuum secondary check ball?

Post by Tuner »

Use the shop compressed air blow tip and with the throttle open blow air down through the choke side primary venturi across the orifice (and hopefully the little brass nozzle) to the passage to the secondary vacuum servo. Ball in or ball out, observe the opening rate and opening force acting on the secondary throttle shaft.

The purpose of the check ball is to slightly slow the initial rate of secondary opening to cushion the effect of a sudden large reduction of airflow through the primary which occurs due to an abrupt secondary opening and results in a bog due to a large change of A/F, such as would occur with a manual secondary with no accelerator pump.
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Re: 3310-1 vacuum secondary check ball?

Post by rfoll »

1980RS wrote: Thu May 25, 2023 1:48 pm Here's what you do, throw the crappy Holley cover in the trash and get a QF adjustable cover. Stick a purple spring in the pod and then go out and make some test runs adjusting the screw in the cover. I did not know how well they worked until I had one on my FST 850 VS carb and was able to dial that carb in perfectly, no bogs, no sags.
I'm not likely to throw away a part I just bought.
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Re: 3310-1 vacuum secondary check ball?

Post by rfoll »

Tuner wrote: Thu May 25, 2023 1:58 pm Use the shop compressed air blow tip and with the throttle open blow air down through the choke side primary venturi across the orifice (and hopefully the little brass nozzle) to the passage to the secondary vacuum servo. Ball in or ball out, observe the opening rate and opening force acting on the secondary throttle shaft.

The purpose of the check ball is to slightly slow the initial rate of secondary opening to cushion the effect of a sudden large reduction of airflow through the primary which occurs due to an abrupt secondary opening and results in a bog due to a large change of A/F, such as would occur with a manual secondary with no accelerator pump.
Interesting Idea
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Re: 3310-1 vacuum secondary check ball?

Post by Joe-71 »

Take a phillips screwdriver and tap the ball seat just enough to leave four small dimples to let the ball seat but not fully. This will give just enough bleed through air to help the diaphram work smoothly and the ball not stick. Done this to dozens of VS carbs, and it works. Joe-71
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Re: 3310-1 vacuum secondary check ball?

Post by Tom68 »

780 on a 383 should be able to handle a pretty rapid opening without bogging, will just need armfulls of lock on wet roads when they open.
Last edited by Tom68 on Thu May 25, 2023 4:46 pm, edited 1 time in total.
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Re: 3310-1 vacuum secondary check ball?

Post by rfoll »

We have had that discussion. The car owner told me he drives it to work every day it doesn't rain. Of course, it rain a lot in Oregon. The Phillips is interesting.
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