Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - SBC with vortec heads and thumpr cam timing/carb questions
View Single Post
  #15 (permalink)  
Old 01-13-2013, 06:54 AM
75gmck25 75gmck25 is offline
Registered User
 
Join Date: Aug 2006
Location: Alexandria, VA
Posts: 1,762
Wiki Edits: 0

Thanks: 4
Thanked 66 Times in 64 Posts
On the Edelbrock 1406
- The idle circuit is mostly independent of the rest of the carb, so if its pig rich at idle you have an idle mixture problem to solve. It may not affect the rest of the carb very much.
- When you get stutter with an Edelbrock under light to moderate acceleration its usually due to step-up springs that are too low (e.g. 5"). The low rate springs delay the transition from cruise to power until 5" of vaccum and the accelerator pump does not provide a long enough shot to fill the transition gap. The carb goes lean and stutters until the vacuum drops enough to allow transition to power mode. Switching to a 6", 7" or 8" spring will let it transition to power sooner as the vacuum drops.
- If you are getting a surge at steady cruise it usually means the cruise step on the rods is too lean. You should be able to use a rod that is 1-2 steps richer in cruise and the same in power.

The Edelbrock carb tuning book provides a lot of good information, but does not emphasize enough that it will work much better if you do certain steps in order.
- Fix the idle mixture first - if you can't fix the idle there may be a flaw with the carburetor.
- Use step-up springs to fix part throttle problems before you start switching rods.
- Don't try to use only the accerator pump shot to fix part throttle transitions. It does not provide a long enough shot to overcome big gaps. Use step-up springs first, then accerator pump.
- Once you get the cruise mixture running right (by swapping rods), then play with other rods to get your power mode running better. You will reach a point where going richer in power has no effect.
- If possible, use an AFR meter to check the mixture while running. Sometimes its hard to "feel" lean vs. rich and you may be trying to fix the wrong problem.

Sets of rods are relatively expensive if you play with many different combinations and you buy one or two rod sets at a time. You probably have to buy them online, and $7/set + shipping can be painful if you buy one set at a time. I bought the Edelbrock tuning kit for the 1406, but it did not have very many combinations on the rich side. You may want to look at the 1405 tuning kit, considering your cam.

Bruce
Reply With Quote