I have an edelbrock dual quad intake and two 600cfm performer quads on top of a rebuilt 427. The throttle is progressive so the rear opens first and then the front one comes on later. I thought in setting this up that it should be idling completely on the rear carb and therefore I set the front carb clear off all the way. I've run the motor three times for around 15 minutes each time. First time I kept the rpms up for break-in. Changed oil after each run.

I called edelbrock tech about something else today and got to visiting with him about the linkage. He said I should be idling with both carbs and if I adjust one carbs idle I should do the same to the other so they are even.

Could I have done some harm to the front cylinders or valves during these three runs? The eldebrok tec said by having the idle off on the front carb that the front cylinders would have been running very lean. I did notice the headers/side pipes were SUPER hot. A lot hotter than my last motor but it had a worn down cam.

Edelbrock said that there are some intake runners between the front and rear carb. There must not be much though if the front cylinders can go lean when idling with only the rear carb. If this is true then I would think the progressive linkage would cause the front cylinders to be lean cruising down the highway??

Could I've damaged anything by running it this way on the rear carb 3 times 15 minutes each? The water temp never went over 180. Could it of scorched the valves?

 

What do the plugs look like front to rear? I'm interested in what others have to say here as well as I’m getting ready to fire up my 427 dual quad setup, but my linkage is not progressive and I’m wondering if I should. I didn’t’ because I’m thinking that the vacuum secondaries on Holley 600s will make it less “on/off”.

I must say that your motor is friggin' beautiful.

 

The plugs don't look bad. I can tell that #1 and #2 were a little hotter than the others but not a lot.

 

You haven't done any harm to the motor by idling only on the rear carb. Exhaust temps at idle are much cooler than any part throttle or WOT running and by then you are out of the idle circuit so it wouldn't matter anyway. However, turning off the idle on the front carb may cause you to have an off idle stumble as the transition from the idle to part throttle circuit may be too abrupt for only the rear carb to manage, thus leaning out the front cylinders a bit. This would be more of a driveability concern than an exhaust temp concern.

Set both carbs up so that both of their idle circuits are working like the Edelbrock rep said.

Your motor IS awesome.

I'm planning to use the same induction setup as you have for the 496 that I'm building.

 

Sounds good thanks LemansBlue68. I'll leave it setup as the Edelbrock rep said and maybe later set them up one to one and see how that goes too. Keep us posted on the 496 your building!

 

The Edelbrock dual quad set-up is similar to the street Hemi stock set-up ......I had one and found the correct tuning to be: 1. Set the carbs to idle equally, balance the airflow between the two. 2. Linkage is set so that normal cruising is done using the front two barrels of the rear carb. 3. At about 40% of throttle, the front two barrels of the front carb begin to open. 3. At full throttle, the secondary air valves allow the rear secondaries of BOTH carbs to open (simultaneously). I always used equal jets on all secondaries. If either the left or right had lean cylinders, I'd stagger the primary jets accordingly as needed........hope this helps, good luck.

 

i don't see how you could have harmed the motor under the conditions you stated