Edelbrock carb: Metering rods & jetting appropriately for altitude
I am setting up an Edelbrock 750cfm carb (#1407) I've already converted it over to an electric choke as well as changed out the metering rods and the primary & secondary jets. As well as modifying the linkage for a custom app.
This carb will be sitting atop a .040" over 350ci, cammed & 10.5-1 compression. A big carb for the engine, I know.
According to the Edelbrock Manual, for every 1500ft of altitude the carb needs to get leaned out by 2%.
Here in Prescott Az we're at 5,400ft and in some parts go higher. That would mean the carb would get leaned out by 7.2%
This is the Edelbrock chart for the 1407
The closest configuration in the chart that would get me to a 7.2% lean is the #22 marker
That would put me 8% lean in the cruise and 10% lean in the Power, this is what I currently have the carb set up as. I also have the secondary jets set for 8% lean
Does anybody see anything wrong with running the carb .8% - 2.8% more lean than necessary? Would I need to add or take out any timing to compensate for the A/F ratio?
Thanks guys ~Mykk
IIRC when over carbing an engine you would want to jet richer to compensate for loss of signal (air velocity). Now a 750 doesn't sound like way too much carb for a healthy 350 but you might want to consider running the secondary side a little richer to avoid being too lean at WOT.
Just my $.02
Personally---I would give the base setting a shot.
I at one time leaned out a QJ on a 350 just a bit and ended up burning exhaust valves and turned the mufflers blue. (but this near sea level on the Central Coast)
Also----given your location, If you insist on leaning it out, #19 would be a better choice.
That would still be usable at Flagstaff's 7000 ft
And Phoenix's 700 ft
I have done the Phoenix to Flag several times (once lived in Phoenx), so it is kinda hard to believe someone would just hang out in Prescott and never venture out.
(BTW---I hope to go back to Az someday to stay---thinking Prescott)
Thank you Bryan,
I'll take your advice and go with the #19 position.
Does your alternator work properly now that you've done the carb swap.
Sort of off topic, I know.
I've been working on pretty much the exact same project for the past 5 months on my few moments of spare time.
A lot of the guys I talk to are saying that the PCM will throw so many codes once all those sensors are unplugged that it won't let the alt. charge right.
I know I'm keeping the oil pressure sensor, coolant sensor, runnin the stock fuel pump with a bypass regulator. That's what comes to mind now, and I'll keep the computer plugged in for simplicity to make the fuel pump work right (this is how I understand it atleast.......)
Ima try and finally fire her up Sunday and see, but I just didn't know if you encountered this at all or if its all just a bunch of jabroni! lol
If you read the Edelbrock manual again, you will see that the rich/lean rod settings are going to based on both the numbers and what you think feels right. Start out with #19 and make your adjustments from there.
- cruise - go as lean as you can without getting a surge (surge usually means too lean)
- power - go as lean as you can without getting any pinging under load
Also make sure you have a set of step-up springs to try swapping, since they seem to be very important in reducing a part-throttle bog or hesitation.
Awesome. I just got my truck running. I don't remember if I said before, it is a SBC in a 99 silverado.
Anyway, I'm not real happy with the way I'm running the fuel and kinda curious what you did with the fuel supply. Did you regulate the fuel pressure using the factory fuel pump or did you go for something else?
I couldn't get the fuel pump to stay on even though it reads oil pressure (something I read would keep it on) so I bypassed it with a key-on hot wire. Now of course the fuel level sensor isn't reading anything and the computer is whining at me as if the engine isn't on. I didn't keep the crank sensor like you did though so maybe our setups aren't that similar.
Any help is very appreciated!
By the way, that sbc sounds bad ***! lol
I ended up pulling the in tank pump, using a piece of 3/8" straight tubing in the factory sending unit and than mounting a email@example.com PSI pump on the frame wiring into the trucks factory fuel pump wires.
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