[Mtume]

I just got a new edelbrock carb model 1405, which is a 600cfm performance calibrated carb. I used to have one just like that only that was the modell 1407, which is the same but with 750cfm.

I bought the new one so that I could save some gas. I got a very mildly tuned 350 with a edelbrock manifold. The problem is that the gas milage is worse with the new one. I turned to Edelbrock and they say its either my timing or the pressure from the elctrical fuelpump. I´m not so sure cause the car runs good, no black smoke or smell of gas. The edelbrock guy insist that I´ll give him the actuall numbers of the timing and pressure, the problem is that would cost me almost as much as an new carb.

Befor a decided to buy this carb, I cheched with edelbrock(the same guy) if the #1405 had the same messurements as the #1407 also telling him what kind of engine I have. Now, when I contacted him, he sad I should have gone with the #1406 which is calibrated for economy. I suggested that I recalibrated my new one, but doesnt think its good idea.

So, what do i do? Recalibrate? What do you guys think is the problem? The gas is almost 8$ a gallon here in Sweden.

 

[rkd]

It will take some tuning, but if you go at it systematiclly, you can probably get some mileage out of one of those. I have not tried tuning my 1406, but it does start and run decently.

I have a lot of experience with Holleys, and have a Holley 600 cfm, model 8005 that will pull down 21 mpg, in my other, non od, carbed hot rod. It had close limit jets, a two stage power valve, reverse idle, etc. The similar not so well tuned 80457 with 64 jets is doing 14 mpg as we speak, on the same car.

Some tuning of the jets/rods, and the vacuum settings should get you some improvement. Timing adjustment, both base and advance will help, and lastly, some appropriate gears.

 

[vrooom3440]

You should be able to get better mileage out of the 600 CFM version of the carb than the 750 CFM.

The Edelbrock tech was right that they do have different calibrations in the manual versus electric choke carb versions. But they also publish the rod/jet calibration combinations used in all the carbs. It should be a relatively easy operation to obtain the rods and jets used on a stock 1406 carb and put them in your 1405.

If you really want to optimize fuel economy though, you are going to have to spend some time and have some equipment. If you are balking at determining what your ignition timing and fuel pressure are you are not going to get there. The ignition timing in particular is the basics that need to be covered first. You will need your ignition timing setup correctly including a vacuum advance to achieve optimal MPG. I might suggest a read of the "ignition 101" thread for more background info there.

Then there is the use of a vacuum gauge along with a wide band O2 sensor. With those tools you can tell what is really going on. But it is gonna cost some money.

 

[Mtume]

The Edelbrock tech was right that they do have different calibrations in the manual versus electric choke carb versions. But they also publish the rod/jet calibration combinations used in all the carbs. It should be a relatively easy operation to obtain the rods and jets used on a stock 1406 carb and put them in your 1405.

That is what I´m thinking. Are those combinations to be found in the manual? I´ve looked it thru and there´s a hole lot of charts and such.

The timing was set by a mecanic two years ago, so I think its pretty good.

 

[vrooom3440]

Yep all the specs are in the manual. Here is an online copy:

http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

For a 1406 calibration you would need a .098" main jet part #1427, and a .075" x .047" rod part #1459.

I don't tend to use the Edelbrock charts anymore as I put together an Excel spreadsheet of ALL the combinations of rods and jets. Edelbrocks charts only show a small portion of the combinations possible. For example the 1406 EC carb calibration is completely off the chart of the 1405 MC carb but obviously can work just fine there.

So from my charts you have a 0.0040/0.0061 jet combination stock in the 1405 MC carb. The 1406 EC carb runs a 0.0031/0.0058 jet combination.

If you changed only your rods to a #1459 7547 you would have 0.0034/0.0061. This is the same power mode you have now and about 2/3 of the way to the 1406 EC carb in cruise mode. This is reference number 25 on your carb's Edelbrock chart BTW.

You could also run a #1419 7542 rod with #1427 .098 jet and have the exact cruise mode of the 1406 EC carb and a power mode slightly richer than the 1405 MC carb.

As for timing... it all depends on the mechanic and the setup. If it is a factory setup then the typical mechanic can do pretty well using the factory specifications. But if is has been modified and the mechanic uses factory specs, well that does not work out quite so well. So many of these cars have been modified over the years that the factory spec are often not applicable.

 

[Mtume]

Thanks for your help Steve! This was what I wanted to know. If the parts isnt to expensive, maybe it could be fun trying different settings.

As for the timing... and the mecanic. He´s a racer aswell, he has an nova doing low eights. And I got a HEI distributer. I think he has got it fairly right.

Thanks again!

 

[Mtume]

I saw a combination in the manual, number 28, which I thought I try out. main jet# 1427 and rod#1456. How does that sound?

 

[vrooom3440]

My spreadsheet shows that setup as a 0.0034/0.0058, or about 15% leaner in cruise and about 5% leaner power mode than a stock 1405 MC carb setup.

Or looking from the other direction... about 1% richer in cruise and same power mode as a stock 1406 EC carb. Probably a pretty good combination to try.

 

[Mtume]

I need a quick answer. I´m going to recalibrate the carb this afternoon and I´m not quite sure where the main jets are located? I know its a pair but I found four of them.

Yes, I´m a newbie

 

[Malibu ss 64]

Since it´s a 4 barrel you have 4 main jets two primarys and two secondarys it´s the primarys you want to change do not know exactly were they are located on a edelbrock carb but I´m almost sure that the ones you want to change are located in the front of carb.

Marcus

 

[Mtume]

Thats the thing Marcus, I need to know which of them is the main/primary jets. I also think it the pair in front, or more in the middle, of the carb. But itwould be nice ta have it confirmed.

 

[vrooom3440]

Ok...

Yes there are four "main" jets on an Edelbrock carb, one for each bore. The two jets in the middle of the carb are the primary jets. The ones in the rear are the secondary jets.

Another way to correlate this is the needles insert into the primary jets. So when you take the top off of the carb you can look where the needles come out of and correlate it with the jets underneath. The primary jets also are in more of a "notch" where the secondary jets are more in the "middle" of the float chamber.

 

[1966_L78]

Note to self; read ALL replies before posting...

 

[vrooom3440]

Note to self; read ALL replies before posting...

???

 

[Mtume]

I got it right, I hope. I went with the model #1406 standard calibration. I changed the jets in the "middle" of the carb. I took the car for a drive and it was good.

Thanks Steve

 

[dpvoiceguy]

Mtume,
If you're chaging jets on your carb, then you're not THAT much of a newbie! The performer series is easy to work on...those are the first 4-barrels I rebuilt as well. I just switched the other way; from 1406 to 1405. (Mine's a bit thirsty!)
Anyway...do you have a portable vac. gauge or can you borrow one? If you're trying to dial it in to get a little better economy you should be setting your mixture using a vac. gauge and (as previously mentioned) you owe it to yourself to know your timing to make sure you aren't chasing your tail. I did this for about a year with my 1406 and a $50 kit of jets and rods. I finally found my problem in the distributor and vac. advance. The car has never run better and I can now make changes to the carb and know that they really mean something. It's been said many times but it's so true...timing first, then carb!
Good luck!:thumbsup: