I have an Edelbrock 1407 (750CFM) carb on my 390 and am experiencing a bog just off idle. I've been fighting the timing battle, thinking that was my problem since I could never get the truck to run well with the vacuum advance hooked up. I replaced the distributor with an MSD billet unit that does not use the vacuum advance. I noticed some performance improvement but still have the bog just off idle. The truck idles well, and when I get past the bog down, it get's up and goes!! But this bog down usually occurs just as am pulling across oncoming traffic from a stop in a turn lane or such!! So, I'd like to fix it. I also have significant backfiring after I really get on it. Are these symptoms of running to rich or poor timing, or both or something completely different?

FYI- I have an Edelbrock Performer RPM intake and a crower Power Beast cam with the folllowing specs:
Grind Lobe Center :292H/112D
Advertised Duration (Intake): 292, (Exhaust) : 302
Duration @ 0.50 in. (Intake) : 214, (Exhaust) :224
Gross Lift(1.76/1.76) (Intake): .521", (Exhaust): .547"

I may be a little weak in the spring department, as I'm still using the stock valve train (Crower said this was possible). I'll eventually upgrade the springs and may try the edelbrock heads again, hopefully avoiding any heli-coil issues this time.

Another observation: if I set the timing by ear, I can get a very smooth idle with enough advance. Should that be possible with a cam with these specs? Should I ignore the smooth idle and target an idle timing of 8-12 degrees anyway? this thing get's very rough or dies around 10 degrees or less.

Any suggestions greatly appreciated.

Greg

 

You got too much carb, 600 cfm is what a FE like best. You should be able to rejet the carb for less fuel flow.

Maybe one of the carb gurus will be here shortly and get you on the right path.

John

jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quiet of night you can hear chevies rusting away.

 

Weak valve springs only cause problems at higher RPM's not off idle. I like that cam you are running. Go ahead and advance your timing to whatever it feels like it should be but be careful of detonation. You air/fuel mixture may need adjusted also. Richening it up a little on the idle adjustment may help. A 600 cfm carb would work fine but with your setup I don't think a 750 is too big. You will definitely benefit from it when you get the edel heads.

 

Ok Your 1407 has>>
Main jet size>>.113 (#1433) secondary jet size >>.107
Metering rod size>> ..071 x .047 (#1453) STOCK ROD

I would suggest to go smaller on the Main jet size..like
>>.110 (#1443) OR even for a trial >>.107 (1431)
With the smaller jets you can then go UP to a `Smaller` meetering rod to get somewhere in between. like .065 x ..037 (#1442)

Since you are not using vacumn advance..Try bringing `IN` the mechanical advance by 2,700rpm ... set the initial at 12-14....
MAX TOTAL advance 38-40

With the `750` cfm you will be seeing LESS velocity through the carb till you get to the `higher` RPM level like 2,000
Bogging may be due to Over Rich condition for street driving, decrease the `shot` from the accelerator pump! give the engine a chance too get the full effects of the bigger carb.




__JOHN__Õ¿ö
FTE Club #7
Member-
http://www.cruisin-north.com/
Santa Rosa, Calif.
72 F-250
ICQ#6030753
http://www.ford-trucks.net/users/jbhf250/
https://www.ford-trucks.com/pictorial/big/1972_f250_2.html

 

Thanks for all of the great info. Look's like I've got some tinkering to do. I didn't notice the bogging down whe I came into work tonight. I advanced the timing a little. I was worried that too much advance at idle would result in way too much advance at higher RPMs, but I can use different stop bushings on the MSD distributor to put a limit on the advance. I'll continue to work the timing until I feel it's at it's best, then I'll work on tuning the carb.

Again, thanks, for all of the help. This is a great site.

Greg

 

I didn't know you could use the stock springs with that cam. I bought it for my 360 which I still need to assemble. I thought I would have to get their springs for it. Would it be safe using the stock ones to break in the cam? Thanks Eric