I'm in the process of rebuilding my carburetor and have a question. I have 4 different sizes of "Pump Discharge Nozzles". There is a 25, 28 31 & 37. These came in the rebuild kit. The size that my carb had was a 31. Now I can see the difference between the ones with and without extensions but what size should I use? I have a jet size of 65. What would I gain or lose by changing the Pump Discharge Nozzle? Also this is just a pure stock 390 and the carb is a Holly 600 CFM. Any suggestions on the jet size also? I never played around with these before. Thanks in advance.

Mike
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1966 500XL 390 C6 Mostly stock at the moment.

Going by the holley performance catalog, the different carb model numbers have different sizes for the same cfm carb. You could try going to www.holley.com and going to the catalogs part, and download a copy of the catalog, if it is the same as the paper catalog it has a section that is called carburetor numerical listing, in there they have a list of the nozzle size compared to cfm, what renew or trick kit is used, and jet size.
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66 hardtop downunder

That's part of the problem. I have the Trick Kit for my carb and in it is a #25, #28, #31 % #37 squirters. It really doesn't say which one to us. Just wondering which I should use.
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1966 500XL 390 C6 Mostly stock at the moment.

Shoters and pump cams are for tuning the carb's response. Before doing any tuning, I strongly recommend that you return the carb to stock so that you have a baseline. You may find that it needs nothing. If you find that you do have running issues, there are various methods to address them when it comes to a Holley.

Smaller shooters let the pump shot occur over a longer time period but with less instant shot. Opposite for big shooters.

The shooters work in concert with the power valve. It's best to get the power valve right first, then work with the shooters and pump cam to fine tune the enrichment circuit. No part of the enrichment circuit will affect the main metering circuit. If the jet is too small, then you have to fix that with a jet change.

That is some of my problem Gerry. The previous owner did all this work. I do know know what stock would be. I have this sick feeling that I am missing something on this carb. I did take some photos before I pulled it off. Right now I don't remember removing a cam!!! Maybe that was my problem to begin with! I'll have to check those photos and look closer at the carb when I get home.
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1966 500XL 390 C6 Mostly stock at the moment.

OK....I found the pump cam....right on the linkage where it belongs! Now I have all kinds of different ones in this kit. Along with the different squirters, which ones should I use. I guess I mean, does anyone know what the stock ones are for a Holley 4160? What do the different cams do? I see that they operate the pump but what are the advantages or disadvantages? How about with the combonation with the different size squirters? Boy I'm going to have fun when I set the float levels!
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1966 500XL 390 C6 Mostly stock at the moment.

Naw, Mike, none of this is too hard. Go to Holley's site an look up the specs for your list number and put it back to stock according to the specs. There are different 600 cfm 4160 models, so you can't go by the conventional wisdom. Go to the source.

I really doubt that you'll have to do much fiddlin' with the carb once it's back to Holley specs. The 600 cfm vacuum secondary carbs are some of their most fool-proof carbs.

About the only part of the carb that you will benefit from tuning is in the secondary spring. The Holley-installed springs are usually way to stiff for anything other than a motor home pulling a full load up the Indio pass.

Hey Gerry,
Downloaded the info on Holley's website. Now I do have a couple of questions for you. About the pump cams....all I got from reading was that the accelerator pump shot is relative to cam color from lightest to heaviest are as follows. White, Blue, Red, Orange, Black, Green, Pink and Brown. Now mine is old but it looks like it could be red. I don't have a red one in the kit that I bought. I can see what these cams do but have no clue as how it effects the running of the car. Also you mentioned the secondary spring.....I have 4 in this kit. They are from the shortest to the tallest, purple, black, silver & green. I haven't taken my old one out yet so I have no idea which one I have in there now but maybe you could shed some light on the subject. How would I benifit from changing springs and which one should I go with.? I guess I'm asking again, how do they effect the running of the car. Thanks for my education Gerry.

Mike
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1966 500XL 390 C6 Mostly stock at the moment.

The red pump cam is the factory cam on most Holleys. The pump cams only "tune" the accellerator pump shot. This is the how much and how fast part of the shot. The factory cam will give a relatively constant volume over the duration of throttle travel. You can change cams to bring in more shot earlier or later in the throttle travel. This tuning would be beneficial in very particular environments, like bracket racing where you may be leaving the line by flashing the converter from idle so you may use the fast pump cam to get you smoothly to booster flow. But this cam would not be ideal on the street in throttle transitions on the highway. For a street-driven car, you would likely use the factory red cam. The pump cams affect the running of the car only in throttle transitions. They have no affect at all under idle and cruise.

As far as the secondary springs...the Holley spring kit, as I recall has six or seven springs. On the package, it tells you which spring is which and what the secondary opening window is for comparison on each spring. Their performance table doesn't relate directly to reality for very many applications but, again, just shows you the affect of the different springs. As I recall, the silver spring is the lightest and will open the secondary the earliest. The spring package is a bit under ten bucks and is worth having. If you don't have the package it came in with the spring performance table, you may want to get a new package so that you know which spring is which.

The secondary springs will allow you to tune when your secondary comes open. Out of the box, it's nearly impossible to open the secondary early enough and completely on most cars. A very heavy car with a numercially low rear gear will probably do fine with the factory spring, but a lighter car and higher rear gear will really benefit from tuning the vacuum motor. The secondary spring tuning will not affect how the carb functions except at full throttle.

I always tune the secondary with the lightest spring as my starting point. If there is a bog in the carb when the secondary starts to open, then you go up a level until the bog goes away. I have never had to go higher than the next to the lightest spring.