AFB Tuning

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What size jets and rods, are you running? Can be as easy as a metering rod change, try a richer rod combo.
 
Slantsix64 said:
Maybe a secondary jet swap?
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Man I don't know. Usually when there's a secondary tip in bog, the air door needs adjusting. Unfortunately, adjusting that one is a bit complicated. I'd sure try a jet change first, though.
 
eekvonzipper said:
Is there a Quick Method to Tune the Transition when you Step-On-It?
Runs Great at Idle, Cruise and W-O-T...
but during Cruise it makes a BlehBleh before it Goes when you mash it.
Choke Fully Open and Warmed Up. I wouldn't mash it otherwise.
It's a Carter 500 on a 273 2bbl engine w/ a Halifax Distrib.
Runs Great other than this One thing...
What is it?

View attachment 1716282055
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Accelerator pump volume?
 
Does it stumble at all if you floor it from a stop? In my experience it's a bit of a trade-off with that style of carbs, if you speed up the secondary air door opening so there's no delay when mashing it at cruise then it stumbles when mashing it from a dead stop and vice-versa.
 
Only happens Once... Floor it in 2nd and you'll feel it burp just once, then No problem to 5k.
Granny shift to 3rd and floor it again, No problem to 5k.
Granny shift to 4th and floor it again, No problem to 100.
 
I honestly don't think I've Ever Launched it Mashed to the floor...
I have a 7 1/4" Rear to think about.
 
I started working with Carter 4bbls in the 1970s. AFB, AVS & TQ. Also Edel later.

I have never used one or tuned one that needed more pump shot than using the outside hole on the pump arm, the least amount of pump shot. Later AFB & AVS,TQ & Edel used a 13/16" plunger. These are 4cc. Std Holley is 3cc, big pump is 5cc. So Carter pumps are quite big.
 
Bewy said:
I started working with Carter 4bbls in the 1970s. AFB, AVS & TQ. Also Edel later.

I have never used one or tuned one that needed more pump shot than using the outside hole on the pump arm, the least amount of pump shot. Later AFB & AVS,TQ & Edel used a 13/16" plunger. These are 4cc. Std Holley is 3cc, big pump is 5cc. So Carter pumps are quite big.
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I say it may be a pump issue. The AFB is an older carb and maybe the plunger is old or hard and you are not getting the full 4cc. I need to change my plunger every couple years when I notice a difficult start. It is a easy try, without removing the carb and doing other adjustments. I would like to note, being your car runs fine, except for that miner glitch, right down all your starting points before any adjustments are made.
 
The problem with just up jetting the secondaries is it takes time to get the raw fuel moving through the boosters. I just remembered, you can pull the secondary boosters and see what the bottom of the emulsion tube looks like. Some are fully open ended and some are very closed off.
DD1E7D03-6061-44CF-BA70-F37D6AE8B4C4.jpeg

Also, Edelbrock 1406 secondary venturi cluster
 
You can play with the secondary air bleeds. I would take a strand of copper from some wire. Slide it in the secondary air bleed hole and bend the top over. I would put a small piece of aluminum tape to hold it in place. Less bleed air more fuel, give it a try. It is easy to reverse.
 
I enlarge the end hole on the E tube on those. The exiting hole can be smaller than the jet, so that the hole is the fuel limiting device, not the jet.
 
eekvonzipper said:
Nah, Runs Great! Pulls Hard all the way to 5k...
just sometimes has a lil stumble when your doing 30 behind some a-hole on the highway and you jump on it to pass.
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Probably no problem with the carb. You just need to be in the right rpm range when you kick in the secondaries. Since you are running a 4 speed, downshift to a lower gear and wind it up a bit (2,500 to 3,000 rpm) then her it rip when you get your chance.
 
Bewy said:
I am not sure if the 500 cfm model has velocity valves [ weights ] in the secondaries. That looks like a factory carb.

What model is it?
Four digit # should be stamped on one of the mounting feet.

Does the carb have a large brass screw in between the idle mixture screws?

I can see one problem: it looks like it has a single plane intake.

Is the engine stock?
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Stock 273 Commando 4 speed Carter AFB. They have very light weighted velocity valves. All 273's use the same velocity valve with the large cut out on the counter weights. The larger valve is from a big block car or aftermarket AFB for comparison.

P1010012.JPG
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There were a number of different vel valves used. I do not know the exact number. Some did not have the U shaped cut out in the blades; I have one that has alum weights molded onto the ends.
 
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