Help with Edelbrock fine tuning....

[bandit67]

Guys, I have very little experience with tuning the Edelbrock carbs and need some understanding. Im taking a used, highly modified 1406 back to stock calibration first and then will proceed to fine tune it for current engine use. Question is, the 1406 calls for metering rod spring to be orange. It currently has a 'plain' spring in which Edelbrock says it's an 8 hg. I believe hg is for a hydro gauge and that is how all the spring colors are listed. Not having a hydro gauge meter, is there a conversion as comparing vacuum gauge settings? I mean we use vacuum gauge setting in determining which power valve number needed with a Holley, can that be done with Eddys also...thanks...

 

[lewtot184]

Edelbrock lists a color/vacuum rating for their step up springs. Edelbrock lists .098 jets .075x.047metering rods with an orange spring for the primary side and .095 jets for the secondary side of 1406; per 2019 catalog. This is going to be pretty lean on the primary side. I use .101 jets, 71x47 rods, and orange springs with the 1406 I use.

 

[pnora]

HG is considered vacuum. All those springs for tuning have a HG after the number.
METERING RODS:
The metering rods are accessible through top of the carb by loosening and rotating their retainer plates. The metering rods use a
small vacuum piston to pull the rod down and a spring to push the rod up in relationship with motor vacuum. High vacuum pulls
the piston down, low vacuum allows the spring to push the piston up. The high/low vacuum relationship corresponds with motor
demands, no/low motor load conditions (cruise) will have high vacuum, high motor load conditions (power) will have low vacuum.
The metering rods are machined with two different diameter steps, smaller at the bottom (power step) and larger above (cruise
step). When the motor is operating at cruise speeds there is no load on the motor and it produces high vacuum keeping the
metering rods down in its cruise mode. In the cruise mode the larger diameter part of the rod is in the primary jet restricting the
jet’s area allowing less fuel through the jet into the primary boosters (lean). When the motor is under power (pulling/load) the
vacuum is low allowing the spring to push the metering rod up into its power mode. In the power mode the smaller diameter part of
the rod is in the primary jet allowing more fuel through the jet into the primary boosters (rich).
Different sized rods change primary overall jet sizing, changing a rod size on either step by one diameter size (.002) is equal to
one half (1/2) of a jet size, making it easy to fine tune the jet mixture. When a jet change is slightly too rich or lean, a rod size
change will usually get you where you need to be.

METERING STEP UP SPRINGS:
The metering springs are rated by the amount of vacuum (HG) required to compress the spring and hold the metering rod in the
down position (they are not rated by weight or length). When vacuum decreases as the throttle opens the metering rod spring
pushes the metering rod up out of its cruise position and into the power position increasing fuel into the motor. In the power mode
the piston/rod is up (low vacuum spring pushes rod up), in the cruise mode the piston/rod is down (high vacuum compresses
spring). The higher the HG rating of the spring in relationship with the vacuum present, the faster the rod will move up into the
power mode and visa / versa. If air/fuel ratios (jetting) are correct, a higher HG spring in most cases will cure a stumble. 8hg
(silver) is the heaviest spring, 3hg (blue) is the lightest. 5hg is normal (orange).

 

[Car #4]

Great explanation @pnora

 

[pnora]

Great explanation @pnora

I stole it off the net. However the poster just needs to use google search and a wealth of information comes up.

 

[R/T Boy 67]

Hg is the chemical symbol for mercury. Basic vacuum gauges measure in inches of hg.

 

[RJRENTON]

HG is considered vacuum. All those springs for tuning have a HG after the number.
METERING RODS:
The metering rods are accessible through top of the carb by loosening and rotating their retainer plates. The metering rods use a
small vacuum piston to pull the rod down and a spring to push the rod up in relationship with motor vacuum. High vacuum pulls
the piston down, low vacuum allows the spring to push the piston up. The high/low vacuum relationship corresponds with motor
demands, no/low motor load conditions (cruise) will have high vacuum, high motor load conditions (power) will have low vacuum.
The metering rods are machined with two different diameter steps, smaller at the bottom (power step) and larger above (cruise
step). When the motor is operating at cruise speeds there is no load on the motor and it produces high vacuum keeping the
metering rods down in its cruise mode. In the cruise mode the larger diameter part of the rod is in the primary jet restricting the
jet’s area allowing less fuel through the jet into the primary boosters (lean). When the motor is under power (pulling/load) the
vacuum is low allowing the spring to push the metering rod up into its power mode. In the power mode the smaller diameter part of
the rod is in the primary jet allowing more fuel through the jet into the primary boosters (rich).
Different sized rods change primary overall jet sizing, changing a rod size on either step by one diameter size (.002) is equal to
one half (1/2) of a jet size, making it easy to fine tune the jet mixture. When a jet change is slightly too rich or lean, a rod size
change will usually get you where you need to be.

METERING STEP UP SPRINGS:
The metering springs are rated by the amount of vacuum (HG) required to compress the spring and hold the metering rod in the
down position (they are not rated by weight or length). When vacuum decreases as the throttle opens the metering rod spring
pushes the metering rod up out of its cruise position and into the power position increasing fuel into the motor. In the power mode
the piston/rod is up (low vacuum spring pushes rod up), in the cruise mode the piston/rod is down (high vacuum compresses
spring). The higher the HG rating of the spring in relationship with the vacuum present, the faster the rod will move up into the
power mode and visa / versa. If air/fuel ratios (jetting) are correct, a higher HG spring in most cases will cure a stumble. 8hg
(silver) is the heaviest spring, 3hg (blue) is the lightest. 5hg is normal (orange).

Hg is an abbreviation for MERCURY and is a vacuum measurement as in mm Hg or milli-meters of mercury on a calibrated scale. The greater the mmHg reading the higher the vacuum (stronger).....just thought you might like to know....
BOB RENTON

 

[Geoff 2]

The easiest way to tune the Edel carb met rod springs is to install the carb on the engine.
Use the stiffest piston springs you have. Swivel the piston cover so that you can see the piston, but it is still retained. Tighten the cover screws.

Warm up engine, adjust idle mixture screws & idle speed. Put in gear if auto. The pistons should stay DOWN & not move. If they do this, job finished. If the pistons move, go the next lighter spring & repeat test.
The object is to use the strongest springs that allow the pistons to stay down at idle.

 

[RJRENTON]

The easiest way to tune the Edel carb met rod springs is to install the carb on the engine.
Use the stiffest piston springs you have. Swivel the piston cover so that you can see the piston, but it is still retained. Tighten the cover screws.

Warm up engine, adjust idle mixture screws & idle speed. Put in gear if auto. The pistons should stay DOWN & not move. If they do this, job finished. If the pistons move, go the next lighter spring & repeat test.
The object is to use the strongest springs that allow the pistons to stay down at idle.

The only thing wrong with this premise is: all idle fuel is metered in the primary booster venturi cluster thtu the "low speed jet" and is non- adjustable (except by drilling). The only fuel access is the bottom of the low speed jet and a calibrated air bleed on the rear of the booster assembly. These orifices also provide the off idle transfer mixture to the point when the VELOCITY of air flowing thru the primary venturii increased io the point where the primary booster venturi nozzles begin feeding fuel. At this point, the primary metering jets, combined with the metering rod diameter begin to control,the fuel flow.

The above pix shows the low speed jet and air bleeds that supply the idle fuel.....for your reference.....one could remove the primary metering rod at this point as the fuel is flowing thru the jet/metering rod and hsve no effect on the idle fuel mixture, except for the idle mixture screws.....just thought you might like to know.....if you don't believe me, inquire of Dragon Slayer, who is extremely knowledgeable.......
BOB RENTON

 

[Geoff 2]

There is nothing wrong with the premise I posted in post #8. It was about how to select spring tension to enrichen the mixture for the main cct.
Yes, one could remove the met rod & it will have no affect on idle. But it WILL be very rich at cruise because the carb is designed so that the thicker cruise step of the met rod is in the jet 'metering' fuel for cruise.
There has to be a method of ensuring the met rod steps [ cruise & power ] are in the jet at their correct positions for cruise & power. Post #8 describes how to do that.

 

[bandit67]

Ok, my thinking was that if vacuum was 18 inches at idle, I should start with what hg spring rating? If my vacuum is 10 what hg spring would I start with?
Using Geoff 2s method, finding the whats needed would be real quick, as there are only five different springs. thanks

 

[lewtot184]

Start with the orange 5"hg spring the carb came with. Edelbrock supplied a booklet with their carbs that walks you through the process of fine tuning the carb. I think it would be near impossible to give exact guidance thru the internet; there's simply not enough information. Get the booklet or go on edelbrock website for the info. I've messed with Carter 4bbls for decades but I still use the booklet and there are still some carter afb/avs websites out there.