Edelbrock 750 - Slow Return to Idle & High Running Temp

[EddieE]

I have an Edelbrock 750 that was on the car when I bought it 7 months ago.  340 was completely rebuilt and stroked by Ryan Johnson at Shady Dell Speed Shop. Now it's a 416.

Engine was dyno'd with this carb, and I've put about 700 miles on it since I put it in the car.  Carb has run well, although I still think it has too much of a stutter coming out of the hole in normal driving with a 4-speed.

Enough history.  Now the engine runs fine, although it runs at about 220 degrees while driving and about 190 while idling.  The symptom I have is a very slow return to idle after acceleration.  If I run the engine up to 2500 or 3500, it SLOWLY comes back to idle.  I looked in the carb and the butterfly seems to be snapping tight quickly, and I checked the accelerator pedal/linkage for any binding and found nothing.  I also checked for any obvious vacuum leaks.  I'm not running any vacuum advance to the distributor.  All ports are plugged at the carb, except the vacuum to the brake booster.  The brakes work fine.

I've heard that a lean condition can cause the high operating temp and a slow return to idle.  I've also heard that this could be a timing issue at the distributor.

OK Einsteins, what obvious cause am I missing? 

[torredcuda]

How much advance in your initial timing and at what RPM does the mechanical advance come in?

[74CudaDave]

I'd say timing - I had to retard the heck out of my engine to get it to pass emissions tests here, and it ran just like you describe.

[EddieE]

How much advance in your initial timing and at what RPM does the mechanical advance come in?

Ryan got most HP/Torque (463 HP and 530 torque) on the dyno with 36 degrees at 2500 RPM.  I dialed it back to be safe to 32 degrees at 2500.  I don't know at what RPM the mechanical advance comes in, but I'd like to if you can tell me how to find out.  I'm also open to reconnecting the vacuum advance, but that's another thread.

My tech told me today on the phone that I should disconnect and plug the vacuum line to the brake booster as the booster may have a leak but is still providing boost.  I'm going to try that first.

Any thoughts?