Rebuild 1406 vs upgrade to 650cfm (Edelbrock)

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

ChuckN

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
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

Full Access Member
Joined
May 13, 2019
Posts
4,135
Reaction score
4,983
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
1406 should be plenty. I would definitely just rebuilt what you have.
 

Bennyt

Full Access Member
Joined
May 17, 2019
Posts
1,018
Reaction score
1,397
Location
Surprise
First Name
Ben
Truck Year
1977
Truck Model
C10
Engine Size
350
Rebuild what you have or go quadrajet.
 

Camar068

Supporting Member
Supporting Member
Joined
Feb 5, 2014
Posts
4,122
Reaction score
2,957
Location
Kentucky
First Name
David
Truck Year
1986
Truck Model
K10/LM7 5.3/4L60e/np208/3.73/32"
Engine Size
10 yrs Air Force
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

Full Access Member
Joined
Mar 22, 2020
Posts
193
Reaction score
111
Location
indiana
First Name
butch
Truck Year
86 and 78
Truck Model
1500
Engine Size
350 and 305
lower your floats if u decide to buy a new one get an avs 2
 

ChuckN

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
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

Full Access Member
Joined
Oct 13, 2016
Posts
2,017
Reaction score
1,808
Location
Northern Virginia
First Name
Bruce
Truck Year
1975
Truck Model
K25 Camper Special TH350 NP203
Engine Size
5.7
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

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
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

Full Access Member
Joined
Oct 13, 2016
Posts
2,017
Reaction score
1,808
Location
Northern Virginia
First Name
Bruce
Truck Year
1975
Truck Model
K25 Camper Special TH350 NP203
Engine Size
5.7
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

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
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.
 

ChuckN

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
@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.

xc_hide_links_from_guests_guests_error_hide_media
 

Novapwr

Junior Member
Joined
Feb 3, 2023
Posts
9
Reaction score
52
Location
PA
First Name
Dave
Truck Year
1978
Truck Model
K10 Stepside
Engine Size
250

ChuckN

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
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

Junior Member
Joined
Feb 3, 2023
Posts
9
Reaction score
52
Location
PA
First Name
Dave
Truck Year
1978
Truck Model
K10 Stepside
Engine Size
250
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

Full Access Member
Joined
Nov 8, 2022
Posts
895
Reaction score
2,544
Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
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.
 

Latest posts

Forum statistics

Threads
41,847
Posts
903,385
Members
33,362
Latest member
Dhatch84
Top