Rebuild 1406 vs upgrade to 650cfm (Edelbrock)

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ChuckN

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Some may have seen or read about my project, but if you haven’t, here’s the rundown.

355ci SBC, flat top pistons (w/ 4 valve reliefs), 64cc camelhump heads. Performer RPM intake, long tube headers. Cam is unknown- haven’t been able to get it to run good enough to see if it has a lope. Brand new rebuild.

I bought it mid-swap, and now want to get it running…right.

Before I go buying a rebuild kit for the carb, should I be looking at a 650 instead? It has a flooding problem even with a 5-6psi Edelbrock fuel pump.

If it has a stock or mild cam, I will likely do a mild street cam like a Comp Cam XE268.

If it were you would you go with a 650 now or just go through and rebuild the 1406 at this point? Thanks in advance.
 

Bextreme04

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1406 should be plenty. I would definitely just rebuilt what you have.
 

Bennyt

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Rebuild what you have or go quadrajet.
 

Camar068

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Some may have seen or read about my project, but if you haven’t, here’s the rundown.

355ci SBC, flat top pistons (w/ 4 valve reliefs), 64cc camelhump heads. Performer RPM intake, long tube headers. Cam is unknown- haven’t been able to get it to run good enough to see if it has a lope. Brand new rebuild.

I bought it mid-swap, and now want to get it running…right.

Before I go buying a rebuild kit for the carb, should I be looking at a 650 instead? It has a flooding problem even with a 5-6psi Edelbrock fuel pump.

If it has a stock or mild cam, I will likely do a mild street cam like a Comp Cam XE268.

If it were you would you go with a 650 now or just go through and rebuild the 1406 at this point? Thanks in advance.
1. rebuild it
2. try cranking the fuel pressure down to 4
3. if your going to buy a new/replacement one, get a Quad or Demon in that order.
 

potent rodent

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lower your floats if u decide to buy a new one get an avs 2
 

ChuckN

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Rebuild kit in hand. Watched a Hagerty video, doesn’t look too bad. Haven’t done a carb since high school with my Nova’s two- barrel.
 

75gmck25

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1406 is not really that complicated, so a rebuild should be straightforward. However, what problem are you trying to cure? High fuel pressure, wrong float level, and poorly-matched step-up springs are the most common problem sources (other than dirt and contamination).

I 2nd the recommendation to try an Edelbrock AVS2 as a replacement. Apparently has much improved low speed driveability, which is good on a truck.
 

ChuckN

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1406 is not really that complicated, so a rebuild should be straightforward. However, what problem are you trying to cure? High fuel pressure, wrong float level, and poorly-matched step-up springs are the most common problem sources (other than dirt and contamination).

I 2nd the recommendation to try an Edelbrock AVS2 as a replacement. Apparently has much improved low speed driveability, which is good on a truck.
Mostly it was running poorly. Dumping fuel and way to rich.

Took it apart today but the guy before me had really aggressive step up springs in it (silver). I set it to stock 1406 +1 stage on the chart. Tomorrow I’m going to do some tuning- it’s not completely happy, have to dial in the choke and I might need to switch out the springs again- I have orange in there now. Has a stutter when I goose it.

Edit- I did completely tear it down and do a rebuild kit on it today.
 

75gmck25

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The silver/ gray spring would make it go from lean cruise to power mode early (8” vacuum), so he was probably trying to resolve a severe part-throttle bog. With a relatively mild engine the orange (5”) should be a better match.

Also check the transfer slot exposure at idle to see that it is about square before you install the carburetor. This should make it easier to set the idle mixture so that there is a smoother transition from idle to cruise.

Check the base timing and see if it runs better by increasing it. My GM engine specs say use 4 degrees, but my engine (aluminum heads, 213/217 @ .050 cam) ) works much better with about 15-16 degrees base and 18 more from the mechanical advance.
 

ChuckN

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The silver/ gray spring would make it go from lean cruise to power mode early (8” vacuum), so he was probably trying to resolve a severe part-throttle bog. With a relatively mild engine the orange (5”) should be a better match.

Also check the transfer slot exposure at idle to see that it is about square before you install the carburetor. This should make it easier to set the idle mixture so that there is a smoother transition from idle to cruise.

Check the base timing and see if it runs better by increasing it. My GM engine specs say use 4 degrees, but my engine (aluminum heads, 213/217 @ .050 cam) ) works much better with about 15-16 degrees base and 18 more from the mechanical advance.
You’re definitely on to something there- I think I’ll hold off on the carb adjustment until I get the tach in and adjust it to my liking.

Do you a distributor that you can custom taylor the ignition curve? I just have the standard HEI. I know the guys on Engine Masters usually will do 30-35 total timing at around 3500. I did that on my old truck with a 327 and an L79 cam and it seemed to like that a lot.
 

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@75gmck25 here is the video of it running. If you listen closely, when I step on it it hesitates. It doesn’t do that every time, but a lot of time it does. The cam sounds pretty lopey, but I have no clue what is inside it. I suppose I could get out my vacuum gauge. I don’t know if it’s a cam that just sounds big and isn’t (like a Thumpr) or it it actually is really aggressive.

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ChuckN

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Read the Edelbrock theory of operation if you already haven't. It's a great guide to fine tuning these carbs. Once you understand how they work, whatever condition you are chasing is easier to recognize and correct. (I had to read it several times till I got it) Lol.


Absolutely! I was just reading that since I last posted on this thread. Where the “stumble” is, is when I goose it hard. Per the manual, that could be the setting on the accelerator pump, not the step up springs. I had forgotten about that! So next time I have it running, I’ll change that either way and see if it makes a difference.

After that, I need some dry weather so I can access test the drivability. But I really need to get that tach in first- gotta make sure I have the timing set before I bother with trying to dial in the carb.
 

Novapwr

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Something I found to be helpful was I wrote down exactly what it was running like and then I noted the changes and how they affected the tune. Early on in my younger days I ended up chasing my tail a few times as I forgot where I was on springs, rods and jets after a few cold refreshments....lol!
 

ChuckN

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Something I found to be helpful was I wrote down exactly what it was running like and then I noted the changes and how they affected the tune. Early on in my younger days I ended up chasing my tail a few times as I forgot where I was on springs, rods and jets after a few cold refreshments....lol!
Great advice! I like a cold snack or three when I’m out in the garage, lol.
 
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