MrJlr

Can I re-jet my 1406 carb up to 750 CFM?
It's either that or buy a whole new carb......

Thanks in advance!

CaseyJones

A 1406 will only flow 600 CFM. That is air flow through the venturis. You can add more gas to the mix with jet changes but you are stuck at the CFM.

Start saving your pennies. Time for a new carb. Sorry about that.

MrJlr

Thanks
Kinda figured that......but at least I know now.....

scottyp99

Please don't take this as an insult, I don't mean it in a negative way, but I have to say that the very nature of your question shows a profound lack of understanding about how a carburetor works. If you spent a little time learning the basic principles of how a carburetor works, you will find that they are much easier to deal with. Here are a few articles to get you started:

http://jalopnik.com/how-a-carburetor-works-496394819


http://www.popularhotrodding.com/tec...buretors_work/

http://www.chevyhiperformance.com/te...uretor_basics/

To answer your question, the cfm rating of a carb is just how much air it is capable of flowing at a certain level of manifold vacuum. The jets meter fuel, and have nothing to do with cfm. A bigger jet will allow more fuel to flow through it, resulting in a richer air/fuel ratio, and a smaller jet will flow less fuel, resulting in a leaner air/fuel ratio. Air/fuel ratio is not one of those things where "more is better", you want it to be just right (like baby bear's porridge) and the jets are used to adjust it. If you want more cfm, you need a new carb, or some serious modifications to your present carb.

Can you tell us why you want to have more cfm? It's possible that what you really want has nothing to do with cfm, and we might be able to help you out with it. Don't be embarrassed, everybody on this forum had a time in their life when they knew absolutely nothing about carburetors. (some still don't, and don't really want to, because they have always dealt with fuel injected cars). But if you have a carbureted vehicle, and want to keep it carbureted, you need to learn a little something about how they work, if only because it will enable you to better understand the answers to questions you may have. Good luck!

Scott

MrJlr

Not insulted......I asked because I really don't know much about carbs.

I have a 383 on the way and they recommend a 750 cfm.
My 1406 is a 600 cfm.
Just wondering if I could get away with the carb I have as it's only a year old.

scottyp99

Your 600 cfm carb will work just fine for a street driven vehicle. They probably recommend the 750 because it generates slightly better numbers on a dyno. You'll only be giving up a few horsepower on the top-end, but the trade off is that you'll enjoy a little better throttle response with the smaller carb. And throttle response is what makes a fast car fun to drive. If it's a really gnarly 383, (huge cam, huge heads, 7000 rpm redline, etc.) the 750 might be worth shelling out for, but that's probably not what you have. You can put the 750 cfm carb on the "maybe someday" list. For now, put your time and effort into tuning the carb within an inch of it's life. A great investment here would be an air/fuel meter, like this:

http://www.innovatemotorsports.com/products/lm2.php

It may seem a little pricey, but it's money well spent.

Scott

MrJlr

Good advise
Guess I'll run it with the 600 and see how she is!

wilcar

You might want to consider rejetting to the 1405 manual choke version which comes with .100 primary jets, .095 2ndy jets and .070x.047 metering rods. This is a little richer than the stock 1406 specs. For normal street driving I found that my mild 350 was running a little too rich with the stock 1405 settings(verified by my autometer wide band afr gauge) so I went with some .095 primary jets. You may find that the 1405 settings may work fine with your 383 for street use. I run a stock 1405 on my 460 ranchero for strictly street driving with no problems.

doorgunner

MrJlr......I also added an oxygen sensor to the exhaust on my 350SBC/Holley600CFM to help me re-jet it for better mpg.

You don't need to do this though if you locate a standard size jet chart for your Holley carb and follow the chart guide-lines.

If your engine "starves for fuel" at 60mph or higher...change the main jets two sizes larger than stock jets and adjust the accelerator pump for a bigger squirt.

(Me being a rookie....you need to wait for experts to post some answers)

7t9l82

what intake are you going to use? if its an air gap type you will likely experience a stumble, if so go up 2 sizes on the squirter, and try it.

SH-60B

Use a 750, you didn't get a 383 just to attend cruise night did you? A 650 will become a restriction at higher RPM, that's why "they" recommend a 750. Ask yourself, how many 750CFM carbs were installed on Chevy smallblocks with a 4 barrel Rochester from the factory? (Hint, all of them) The big blocks got 850CFM.

MrJlr

What is the CFM of my original Q-Jet (I still have it!)

SH-60B

750

MrJlr

Hmmm.....maybe I should send it off to Lars.....???

SH-60B

Or SMI

MrJlr

Just sent Lars an e-mail......I'll see what he says...

Thanks for all the tips!

Yeller81USNRet

In French Carburetor means " Don't F**K with it "

Jebbysan

My 383 El Camino had a 600 Edelbrock on it and it loved it...although it ran only cleaned up stock 882 heads and a XR274 Hyd. roller cam...headers, performer...etc.....

Tell us a little more about your 383?

Jebby

MrJlr

It is this:
http://www.blueprintengines.com/inde...1-engine-specs

It will be delivered tomorrow (tracked on Fedex)

Jebbysan

Ooooooh.....you are going to need a 750 for that power level....

You will be happy with blueprint....I have installed and got their product
running.....

Jebby