Ok, I finally got my 79 Z all back together and running, and I wanted to replace the jets in the carburetor. It dynoed 279rwhp/345rwtq before, but was running at 12:1 towards the top end which is lean, correct? Its a holley 750 with vacuum secondaries (List 3310-3 1370), and the stock springs.

I want to get the quick change spring kit for it, and was wondering what springs and jets i should go with? I'm not really sure what parts to buy or where to buy them. I would preffer if i could get them on Ebay. Could someone help me find them? This is my first carbed car.

[This message has been edited by Shawn MacAnanny (edited December 01, 2004).]

12:1 is actually very rich. Is the carb box stock? I think the 3310 came with #72 jets in the front. They used a metering plate in the rear.

[This message has been edited by 1978LT (edited December 01, 2004).]

So can i fix this? I was thinking correct A/F was 11:1, but now i remember it's 14.1. This could be the cause for my loss of power right?

If i hook up an A/F gauge will that help at all? Is there anyway to lean out the mixture?

The BEST way to get the proper adjustment is on a wideband O2 on a dyno, while changing jets and timing.

But you CAN change the jets in the carb as long as you change the fronts/rears in pairs, and keep them with 5 numbers of each other as a general rule.

14:1 is cruising ratio
at WOT racing 12:1 is about right

The springs will help alot you just keep going lighter until you get a hesitation then go up one(or do what i did put the lightest one in and make everything else work with it! cost more though)

12:1 is a little rich but not horrible. 13:1 is about perfect for a WOT AF mix. 14:1 is lean for WOT, but good for cruise.

I think the best way to get it a little leaner on the top end would be to use a lighter spring in your secondaries -- not the lightest, just a step or two lighter.

I'd try the purple spring and run #70 jets in front (72's are stock, but tend to be rich on a small block).

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Mid 11's on pump gas, all motor . . . and no trailer.

So i need to get smaller jets?? How about I try the spring thing first? Is there anyway i can check A/F without a wideband? I mean i know there are gauges, but i honestly dont know how they work or measure it. I like to know the mechanics of something before i try to use it.

I have heard A/F gauges arent very accurate. Is that true?

I dont think a lighter spring will help mixture because the mixture is controlled by airflow through the boosters in the venturi.
without changing jetting the mixture should remain the same ratio for any given amount of airflow.
you'll need to add a metering block to the back of that carb so you can change jetting,
you'll need a block off the rear of a 600-750 without the provision for power valve, or they sell a kit in summit i think its about $50.00 bucks adding the block will require extending your fuel line but you can cut that inbetween the bowls add a 3" pc of 3/8" fuel line (makes it easier for removal anyway)


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1972 Camaro 350 factory heads 1.94/1.5 street driven full interior everything works 7.59
89.54 mph

The metering plate in the back is equivalent to a #75-76 jet. That is just fine -- while a rear metering block is a nice thing to have I don't think you really need it at this point.

Changing the rear spring to a lighter one will make the secondaries open quicker and more fully at WOT. While it is true that a stronger signal across the venturi will pull more fuel, velocity will be reduced through the secondaries with a lighter spring. Lower velocity means a weaker signal will make the secondary a little leaner.

I've played with the O-3310 a LOT on my 383 and I found that my engine ran fastest with the Yellow spring and a #70F/#74 rear. I used the Purple, yellow and white springs to fine tune -- there was not a real big difference between how these two ran.

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Mid 11's on pump gas, all motor . . . and no trailer.

So what about the A/F gauge? Should i get one and check it before, then after i add the springs?

You might as well go ahead and get the spring kit if your keeping the carb youll improve performance after fine tunning the spring.

Fellow member Onovakind67 is in the hi performance industry. In another post he stated that on one dyno run he manually opened the vacuum secondaries on an engine and it gained 20 or 30 HP!! The stock Holley supplied spring is almost always too stout. That is why I am leaning more towards the mechanical secondary carbs these days. You KNOW you are getting full throttle!

Best way to tell if you are making more power (and the funnest way) is to take it to the track and watch your trap speed. If the trap speed goes up its making more power. Make sure you only change one thing at at time or results will get confusing.

The problem with a dyno is that it is only a simulation and doesn't accurately duplicate the loads and acceleration rates that the engine actually sees in the car at the track.

What makes more power at the dyno may cause driveability problems when actually in the car.

I'm not saying dynos are bad, just that you have to be careful -- what works at the dyno may or may not work in the car.

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Mid 11's on pump gas, all motor . . . and no trailer.

Ok, well im getting the spring kit, but no one has answered my question about the A/F gauge. Should i get one of them?

I guess its up to you do you want one could cut down wear and tear by tunning at the track youll have it pretty close before you get there i wouldnt mind having one myself.

<font face="Arial,Verdana" size="2">Originally posted by Shawn MacAnanny:
Ok, well im getting the spring kit, but no one has answered my question about the A/F gauge. Should i get one of them?</font>

A wideband would be nice but pricey, a narrow band won't be accurate enough to help with your fine tuning.