Left or right idle screw

[73 T&C]

dumb question:

Balancing left right side of carb.

The manifold vacuum take off at the rear: is it on the left (passenger side) plenum or right?

Pulled #1 and it looked white (lean).

Raised the idle mix a 1/4 turn both sides to 1-3/4 left and 2 full turns on the right. Thinking I got them backward and would rather not remove carb to confirm.

 

[73 T&C]

This ELB is totally different from my 73 440 that I can tune with my eyes closed.

 

[CBODY67]

Consider the plenum as a reservoir which all of the runners feed out of. Unless there is a full (all the way to the bottom of the carb) plenum divider, "rh" or "lh" usually makes no difference with respect to manifold vacuum. Some engines have ONE vac tap on ONE cylinder's runner as others have it on the back of the carb.

In "balancing" the idle mixture, start with the idle screws turned outward equal amounts. The old spec used to be 1.5 turns out, from a lightly-seated position. Then start the car and set the base hot base idle, then tweak/fine tune the mixture screws for the highest idle speed. If the idle speed rose too much, readjust the speed down and re-tweak the idle mixture screws. IF turning one screw has little affect as turning the other one has more affect, time for a carb teardown.

Idle mixture probably will NOT color a plug very much, unless it's way too rich. Best way to look at the plugs is after many 1000s of miles on the road OR at the end of a 1/4 mile drag strip run. The carb's main jets or main jets w/metering rods have a much strunger affect on spark plug insulator color, by observation.

CBODY67

 

[73 T&C]

Ok.... looked it up.

Cylinders 2,3,5 & 8 are fed from the passenger side of the carb. Top plenum. Cylinders 1,4,6 & 7 are fed from the drivers side of the carb. Bottom, lower, plenum.

Manifold vacuum taps into the #7 runner just after split to 6&7.

Balanced carb. Slightly richer idle on the drivers side... makes sense.

 

[commando1]

This is why I luv'ya, Javier.

 

[73 T&C]

This is why I luv'ya, Javier.

View attachment 204500

How did you get a picture of the inside of my head????

 

[commando1]

How did you get a picture of the inside of my head????

We're alike. Fortunately my severe A.D.D. keeps me from becoming obsessed.

 

[CBODY67]

Ok.... looked it up.

Cylinders 2,3,5 & 8 are fed from the passenger side of the carb. Top plenum. Cylinders 1,4,6 & 7 are fed from the drivers side of the carb. Bottom, lower, plenum.

Manifold vacuum taps into the #7 runner just after split to 6&7.

View attachment 204448

Balanced carb. Slightly richer idle on the drivers side... makes sense.

Ahhh, you've got one of those electric-assist choke, full plenum divided, EGR's pieces of spreadbore carb cast iron!

HOW MUCH richer on the driver's side? "Makes sense"???

Just curious,
CBODY67

 

[73 T&C]

On this car... about 1/4 turn. On the wagon just a smidge.

But on this car, the needles are sharper so I’m figuring they are about the same..... no egr.

 

[CBODY67]

In the picture, the surface casting over the lh exhaust crossover is where an egr valve would go. It might have a block-off plate and gasket. The holes in the primary sides of the manifold are where the egr enters the manifold to go to the cylinders.

CBODY67