Hi all, trying to lean out my dual quad. When measuring vacuum to figure step up springs, run gauge off manifold vacuum I assume?
Edelbrock springs 1406 and 1405
- Thread starter 4spdragtop
- Start date
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Yep
Yes sir and when choosing step up springs, you choose HALF what the gauge reads. So if the gauge reads 12hg, for example, choose the 6hg springs.
Thanks guys, and whatever reading is on gauge, you divide in half for the spring "size"?
Eg 14" on gauge=7" springs?
Eg 14" on gauge=7" springs?
Correct!
Use the spring rated for HALF idle vacuum.
j par
Well-hung Member
Oddly enough I have different springs and primary jets in each carburetor... same secondary jets...
That doesnt seem odd at all really. It's getting to find the right combo.
I have to disagree with RRR about the method of choosing the correct step up springs. You need to swivel the piston tops so you can see the pistons. Use the strongest springs that will just prevent the pistons from moving [ lifting up ], engine idling, in gear. Once these are known, you can try lighter springs but you might get a bog because it is too slow to enrichen the mixture. Prolly only do this for economy, but I doubt that is a worry with two carbs...
Thanks, that's what I did in the video. Heres another vid showing them a little better with tops swiveled. I'll chk with it in gear idling.
Plugs look rich. That's why you want lighter springs. They delay the metering rods getting into the rich part of the metering rods. With a spring too strong, the rods stay in the rich step at idle, causing an overly rich mixture. What's the specs on your cam, Steve?
Then you will be disagreeing with both Holley and Edelbrock, as they both say to cut the manifold reading in half to make the spring choice, just like the power valve. Although I use cruise vacuum with the Holleys, both say that the metering rod carburetors are very difficult to get a good cruise vacuum reading on and I have verified that on the vacuum gauge. The LEAST little difference in the gas pedal or least little incline makes a big difference in the vacuum reading, but the Holley power valve is easier to use cruise vacuum. I JUST got off the phone with the Holley tech line this morning discussing this as I am tuning on my 625 Street Demon. They said word for word to use idle vacuum and cut the direct reading in HALF to make your choice for springs. Since Edelbrock uses the exact same springs, their method is the same and I have verified that with Edelbrock as well, trying to tune this 1407 750. The Street Demon however, is head and shoulders better.
Thanks Rob, its waaayyyy overcammed Rob. Comp 20-246-4. 340 cam in 273 lol. But it wasnt this rich with LD4B/1405. Those plugs are brutal lol
The manifold vacuum reading....its the reading at idle and in gear?
Weird how this thing fires off right away and runs "good" until about 10-15 minutes in I'll get a "surging" issue.
Weird how this thing fires off right away and runs "good" until about 10-15 minutes in I'll get a "surging" issue.
No sir. That's nowhere NEAR as overcammed as you think. In fact, I completely endorse that! You need to remember, solid cams genreally "act" about ten degrees duration LESS than their comparable hydraulic counter parts, so that's comparing to a hydraulic that's about 214 @.050. 224 @.050 is very mild for a solid. I'm all over that combo. That's a goodun. What's the max idle vacuum you've gotten so far?
Yes, if it's an auto, put it in gear to measure the vacuum.
Thanks, I havent messed with it much, so idle in park is 12". More tweaking to come, but I've already gone 1 step leaner with rod/jet. Springs were going to be next. But was unsure of changing those lol.
I'm unsure I would change the rods YET. I like to zero in on the springs first and you need the 5hg springs. I believe they are orange. I say the springs first, because if you make more than one change at the time, you don't know for sure what improved it or made it worse. Since we now KNOW it needs the 5hg springs, that's what I would do first. The closer you get to "right" the more vacuum you will read on the gauge. If you make a "wrong" decision, you will see that as well. But the 5hg springs are the "right" first step.
in other words, what I am saying is, the rods and jets are "usually" pretty close. You normally only need to change those if the combo is more radical than mild and yours is not.
I'll be danged if I can remember. The 1405 is the "performance" version of the 600, so the orange springs would make sense, since they would start to release the metering rods at "about" 10hg, which would be indicative of a mild, non stock camshaft. I "thought" they all came stock with the plain spring, but you may well be right.
Manual states "base calibration" is 5", which is the orange. I've tried to decipher which is which, but these dang springs have color wore off of some of them. See pic.
I thought I saw a blue tinge to the springs that are installed. If it is blue, that's the leanest spring, so why in the heck is it so rich?
Is there something "more" to the spring than the inches of vacuum? Height maybe as well?
I thought I saw a blue tinge to the springs that are installed. If it is blue, that's the leanest spring, so why in the heck is it so rich?
Is there something "more" to the spring than the inches of vacuum? Height maybe as well?
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Do those plugs look like that from idling or driving ?
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