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  #16 (permalink)  
Old 01-13-2013, 07:27 AM
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Quote:
Originally Posted by 75gmck25 View Post
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

This is all good info, but none of it is relevant until the timing set up properly for this cam. Thumprs are very difficult to set up for the street and if you don't have the proper initial timing and short curve it will never run right. If the timing too far retarded at idle, the throttle plates will need to be opened more to allow it to idle. This causes a tuning problem if the carb is not utilizing the idle circuit because of the throttle blades being opened too far. The timing MUST be set correctly before the carb is tuned or this set up will never run.

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  #17 (permalink)  
Old 01-13-2013, 07:54 AM
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Originally Posted by tcarlx View Post
The truck bucks the starter warm at 16 initial. Is the 22 including vacuum. I am guessing not since u said to run ported. Worth a shot. Thanks for the info.
To allow running the base inital timing that the motor wants with a cam like that, install and use a simple ignition power interupt toggle switch to aid hot cranking/starting. Install the OEM GM starter motor end brace too.

Its just that easy. 26deg inital timing 10deg mech curve 36deg total.

10deg of vac advance for cruising at part throttle.

You will never get it right until you give the motor the generous base timing it needs to idle correctly.
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Old 01-14-2013, 09:08 AM
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So I played with the truck a little this weekend and to my suprise it does start with 23* initial(no comments needed here). I unplugged the vacuum advance and its all in at 36*. Now come the questions.
Are my only options for limiting my mechanical to braze or stick something in the hole on/next to the center plate? Is there anything I can purchase for my HEI that would limit/ allow my to have only 10-12* mechanical?
Is it normal for my timing to bounce around slightly when check it with the light?
I didnt get to drive it without the vacuum advance plugged in to see if it shutters/bucks/bogs but will sometime this week. Just for reference when I built the motor I used a piston stop to find 0 on the dampner and have timing tape on it so its accurate. Thanks to everyone that posted on here. I will be back when I have more info.
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Old 01-14-2013, 01:42 PM
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Quote:
Originally Posted by tcarlx View Post
So I played with the truck a little this weekend and to my suprise it does start with 23* initial(no comments needed here). I unplugged the vacuum advance and its all in at 36*. Now come the questions.
Are my only options for limiting my mechanical to braze or stick something in the hole on/next to the center plate? Is there anything I can purchase for my HEI that would limit/ allow my to have only 10-12* mechanical?
That's the easiest thing to do. Once you get the hole tapped and the head of a few screws ground down (most times it takes a few tries to get it perfect), the rest is easy.

There is the option of buying an MSD distributor then forking out for custom bushings ($33), but that's a lot of money.

Quote:
Is it normal for my timing to bounce around slightly when check it with the light?
Timing hunting around can be from a chain w/too much play, the cam walking in and out (is this a retro roller w/a cam button?), excessive distributor end play, wear to the distributor/cam gear(s), a damper w/a loose outer ring, a loose damper-to-crank, to name a few.

Quote:
I didnt get to drive it without the vacuum advance plugged in to see if it shutters/bucks/bogs but will sometime this week.
If it's limited to 10-12 degrees you shouldn't have any surging like can happen if there's too much timing at light throttle cruise when the vacuum advance is all in. When you get ready to hook it back up use ported vacuum.
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Old 01-15-2013, 12:17 AM
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What is the final reaer ratio and tire diameter? It makes a huge difference.
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1406 edelbrock 600, rhoads lifters, sbc thumpr cam, sbc vortec heads

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