Edelbrock/Carter style carbs are junk. Throw it away and get a Holley 650 Double Pumper. The throttle repsonse will be much better and the Holley's have much more tuning capabilites

 

750 CFM is too much carb for a 351M. The primary venturis are 1 7/16" diameter on an Edelbrock 1407. An Edelbrock 1406 has 1 3/16" diameter primary venturies. That means the carb opens faster. If the carb opens too fast then the metering won't be right and it will bog. You can help it by putting the accelerator pump rod into the hole closest to the carb body. This will give you faster action from the pump.

Check your plugs for color. If they are tan, then your mixture is OK, if dark you may be rich. Rich mixture will cause similar problems. Check your rods and jets. A 1407 should have 0.113 main jets and 0.071 X 0.047 Rods. Lean mixture can cause the same problems. If your plugs are white, you may be lean. The vacuum surging at idle and the rich smell is a problem with the idle mixture. Edelbrock recommends to get the maximum speed by turning each adjusting screw counter clockwise(rich) and then backing off until the speed drops 20 rpms.

Another point that Edelbrock makes is if you have a long duration camshaft to run as much initial advance as possible. I have mine set to 10 degrees initial, and cut my vacuum advance down to 2 degrees, to keep the total to 36 degrees (24 mech +2 vacuum +10 initial). You could also reduce the mechanical advance by recurving the dist. You could also connect your vacuum advance to manifold vacuum to get full vacuum advance at idle, and none at higher RPM's whennthe mechanical advance takes over.

Put a vacuum gauge on it. If the vacuum is below 7" Hg at idle, then you need a weaker step-up spring. Your rods a probably up in the Power mode at idle causing a rich mixture.

 

I've a pretty similar problem with a 351W and a Street Avenger (670cfm). It'll bog everytime off-idle I step on the gas.

Can adjusting the float level fix the problem?

Thanks.

Ben

 

Bogging off idle is usually due to a lean condition, but it can be other things. Float Level is not one of those things. The fix that usually works is to adjust the accelerator pump to get fuel earlier and faster. If your fuel level is too low in the bowl, and the pump doesn't start to pump right away, then adjusting the float level will help, but that is because the float level wasn't set right to begin with.

 

Heres another interesting one, I had a CJ7 with the small block AMC V8 and it would do exactly that...pulled my hair out. It turned out being a very loose timing chain, it was that way from the shop that rebuilt it. put in a new one and it got rid of that problem.

 

Not sure if you ever got your off idle stumble fixed but for my '79 stock 351m, it was the advance canister. I messed with the carb, the vacuum lines, the choke, etc. and finally realized my vacuum advance canister was shot. Put ona new one and the stunble disappeared. I had to re-tune my timing a bit, but otherwise was fine.

 

Yea, Ive still got that lil stumble right of idle and I hate it... But I havent been home much to tinker with my old truck like I want to.. Im going to school now and its in North Carolina and I dont get to come home much to fool with it...

 

I had the exact same problem with a 400 and 750 edelbrock. The only thing I can figure out is that the transition slot isn't set up right when you over-carb with an edelbrock. It takes too much movement of the throttle blades to activate the pump shot, which then causes a lean condition due to the transition from idle to main jet not being set up, or tuneable like a holley. I took mine off and put on a 600 that I had, and it got rid of the problem all together. My top-end suffers a little, but it hasn't bogged down or stalled out on me yet. When you watch the throttle and you crack it open while idling, watch how far you have to open the throttle before the accel pump gives any fuel. If you play with it long enough, you will eventually see that the dead spot is right where the slack is in the linkage. Unless you have an idea how to improve this, I think that it's gonna take a carb swap to cure it. As for the holley problem, I think it's very similar, but more tuneable on a holley.