[Cliff R]

At light engine load with the throttle plates nearly closed a good portion of the fuel to the engine comes from the idle mixture screw holes and off idle transfer slots. Large bore carburetors with small boosters rely on this more than smaller bore carbs with more booster area, like the TQ and Quadrajet.

The accl pump is NOT a player in that range, it is only there to cover up a momentary potential lean condition going QUICKLY to heavy or full throttle, or any really quick throttle movements. If you are "easing" into the throttle and seeing a lean spot, surging, hesitation, stumble, bog or just "flat" and not picking up speed as quickly as it should, you need to add fuel to the idle system more times than not.

As far as accl pumps go, the lip seal type pumps are not nearly as effective or desirable as those that use a garter spring to keep the pump cup in constant contact with the bore. I still see those older accl pumps showing up in rebuild kits for Q-jets and they don't make the grade, plus the "blue" or "black" seal on them is a complete POS and will not hold up in this new fuel. I have tens of thousands of "blue" seals removed from accl pumps to install a good one if anyone wants any samples to test PM me and pay the shipping and you'll have a small bag of them at your door in 2-3 days.......Cliff

[67gtospud]

Quick update on the stumble:

I removed both carbs to find the secondary transfer slot was exposed more than the primary carb's slot. After setting them equal and resetting idle this tremendously helped eliminate the stumble. Along with the vacuum advance connected its gone. I did also change up my timing curve. It's now 16 initial, 32 total. VA is adding 10 degrees.

After resetting the carbs, the best vacuum I can achieve is 6" at idle. I'm idling at 850rpm. It still diesels when I shut the car off. I tried 900rpm but it dieseled more than it does at 850. I can get the car to idle down to 750-800 and the dieseling is nearly gone however the best vacuum I can achieve at that speed is 5".

The last issue I can't seem to sort out is when I'm cruising my afr Is hovering around 12.5-13 unless I add just a hair of throttle. Then it'll happily sit at 14 BUT with this additional hair of throttle the car is accelerating. So I'm constantly speeding up and slowing down. I dropped the step up springs back down to the 4" ones and same thing. I will try to test drive again this weekend with the lightest (3" blue) springs but I'm not confident that will solve this slight issue.

[Kenth]

You need to feed that engine with proper amount of combustible A/F mixture at the right end.
The symptoms is NOT cured by adding ignition lead, accl pump shot, power piston springs or main jets.

Until you open the idle/low speed jets/tubes you´re just chaing your tail.
Start with .002" larger than present.

JMHO

[67gtospud]

Originally Posted by Kenth

You need to feed that engine with proper amount of combustible A/F mixture at the right end.
The symptoms is NOT cured by adding ignition lead, accl pump shot, power piston springs or main jets.

Until you open the idle/low speed jets/tubes you´re just chaing your tail.
Start with .002" larger than present.

JMHO

You're talking the idle air bleeds correct?

[Kenth]

No, i´m talking of the idle tubes, in the primary venturi nozzle assemblies, feeding fuel into the idle/lowspeed cicuit.

[steve25]

Why don’t you try a Easy experiment?

Close down the mixture screws on one carb and set the other to idle the motor off of.

In doing this does the motor still run on in the same rpm range?

If not then this proves all the more for the need for what you are being instructed to do in post 43.

[67gtospud]

Originally Posted by Kenth

No, i´m talking of the idle tubes, in the primary venturi nozzle assemblies, feeding fuel into the idle/lowspeed cicuit.

Ahh ok. So opening these up allows more fuel correct? My idle mixture screws are currently 1 turn out from closed and it Idles around 14:1. At this point it makes the best vacuum.

Originally Posted by steve25

Why don’t you try a Easy experiment?

Close down the mixture screws on one carb and set the other to idle the motor off of.

In doing this does the motor still run on in the same rpm range?

If not then this proves all the more for the need for what you are being instructed to do in post 43.

I will try this. The run on only happens when the engine is fully warmed so I will see what happens

[77 TRASHCAN]

Originally Posted by steve25

Why don’t you try a Easy experiment?

Close down the mixture screws on one carb and set the other to idle the motor off of.

In doing this does the motor still run on in the same rpm range?

If not then this proves all the more for the need for what you are being instructed to do in post 43.

and post 3

[67gtospud]

Originally Posted by 77 TRASHCAN

and post 3

My idle mixture screws are 1 turn out. At this point are my best vacuum readings. If I fatten all 4 screws up 1/4 turn vacuum drops to 5".

[77 TRASHCAN]

Originally Posted by 67gtospud

My idle mixture screws are 1 turn out. At this point are my best vacuum readings. If I fatten all 4 screws up 1/4 turn vacuum drops to 5".

Ok, no ill will intended.

[steve25]

The idle mixture screws on any Carb provide a homogenized mixture of fuel and air if I am not mistaken.

[Formulas]

If your spark plug coloration isnt already to cold going cooler on plugs will help with run on

They over say a piston top or combustion chamber are more likely to auto ignite if to hot

Carb problems are often times misdiagnosed from other issues and via versa

[67gtospud]

Originally Posted by Formulas

If your spark plug coloration isnt already to cold going cooler on plugs will help with run on

They over say a piston top or combustion chamber are more likely to auto ignite if to hot

Carb problems are often times misdiagnosed from other issues and via versa

I'm currently running NGK heat range 7 plugs. I thought about going 1 step colder but not exactly sure how to read if my plugs are too hot or too cold

[PontiacJim1959]

Originally Posted by 67gtospud

Quick update on the stumble:

I removed both carbs to find the secondary transfer slot was exposed more than the primary carb's slot. After setting them equal and resetting idle this tremendously helped eliminate the stumble. Along with the vacuum advance connected its gone. I did also change up my timing curve. It's now 16 initial, 32 total. VA is adding 10 degrees.

After resetting the carbs, the best vacuum I can achieve is 6" at idle. I'm idling at 850rpm. It still diesels when I shut the car off. I tried 900rpm but it dieseled more than it does at 850. I can get the car to idle down to 750-800 and the dieseling is nearly gone however the best vacuum I can achieve at that speed is 5".

The last issue I can't seem to sort out is when I'm cruising my afr Is hovering around 12.5-13 unless I add just a hair of throttle. Then it'll happily sit at 14 BUT with this additional hair of throttle the car is accelerating. So I'm constantly speeding up and slowing down. I dropped the step up springs back down to the 4" ones and same thing. I will try to test drive again this weekend with the lightest (3" blue) springs but I'm not confident that will solve this slight issue.

You may have posted this, but I may have missed it. Is your vacuum advance hooked to manifold vacuum or a ported source on the carb?

If you have manifold vacuum, it will pull in the vacuum advance as soon as you connect it. So if you have set your Intial at 16 with no vacuum advance, connect the vacuum advance to direct vacuum, you now have 26 degrees Initial (16 + 10 = 26) which is way too much and may be contributing to your fast idle speeds. You should shoot for 20-21-ish Initial with the vacuum connected to manifold vacuum - which means Initial at the balancer with the vacuum advance disconnected should be set at 10-12 degrees. See if that will drop your idle RPM's down any.

Dieseling is from too high an idle RPM which can mean the throttle plates are still to far open and allowing gas to be siphoned out through the idle mixture slots - thus your idle speed isnt dropping.

From other carb issues having high idle, make sure the throttle plates are capable of closing completely. Could be hanging up or hitting a gasket?

Next seems to be the idle bleed tubes may require opening up to allow more air through at idle - this is just a suggestion.

5-6 inches of vacuum sounds like a vacuum leak somewhere - that is extremely low. Power brakes? Brake booster? Brake booster check valve?

Sometimes it is best to make a block off plate for one of the carbs so you can work with one at a time and see if blocking 1 off changes any of your numbers - it could isolate the issue.

[67gtospud]

Originally Posted by PontiacJim1959

You may have posted this, but I may have missed it. Is your vacuum advance hooked to manifold vacuum or a ported source on the carb?

If you have manifold vacuum, it will pull in the vacuum advance as soon as you connect it. So if you have set your Intial at 16 with no vacuum advance, connect the vacuum advance to direct vacuum, you now have 26 degrees Initial (16 + 10 = 26) which is way too much and may be contributing to your fast idle speeds. You should shoot for 20-21-ish Initial with the vacuum connected to manifold vacuum - which means Initial at the balancer with the vacuum advance disconnected should be set at 10-12 degrees. See if that will drop your idle RPM's down any.

Dieseling is from too high an idle RPM which can mean the throttle plates are still to far open and allowing gas to be siphoned out through the idle mixture slots - thus your idle speed isnt dropping.

From other carb issues having high idle, make sure the throttle plates are capable of closing completely. Could be hanging up or hitting a gasket?

Next seems to be the idle bleed tubes may require opening up to allow more air through at idle - this is just a suggestion.

5-6 inches of vacuum sounds like a vacuum leak somewhere - that is extremely low. Power brakes? Brake booster? Brake booster check valve?

Sometimes it is best to make a block off plate for one of the carbs so you can work with one at a time and see if blocking 1 off changes any of your numbers - it could isolate the issue.

Vacuum advance is connected to ported source. The vacuum can doesn't begin coming in until about 12" vacuum so I get no additional advance at idle anyways.

The throttle blades are capable of completely closing. They're currently set that about .020" of the transition slots are showing with the throttle plates closed.

By opening the idle bleed jets/tubes what change would that make to my idle mixture screws? Will opening the jets allow more air or more fuel? Will this increase my base rpm? As I posted my mixture screws are currently 1 turn out from closed.

I've check 3 times now for a vacuum leak. Twice with propane and once with carb cleaner. I'm about ready to build a smoke machine and see what I come up with.

I am running hydroboost brakes so no vacuum lines there. The only vacuum lines I have is 1 to the vacuum advance and 1 on the back of the primary carb down to the pcv valve.

Is it possible my pcv valve isn't operating properly due to not enough vacuum thus creating a large, unmetered leak inside the engine?

[Formulas]

Plug reading without pictures

Basically you want gray white any color than pitch black about half way down the ground strap

Same with center electrode except at the tip and extended from the tip a bit

Basically hot enough at speed to keep vicinity of the spark hot enough to burn off contamination so it doesn't foul / fail to ignite,
anymore heat than that is not productive

Some plugs heat range and numbers go different directions than others

I fought run on with #48 heads on a 440 with flat tops 2 valve reliefs in the early 80's this is PART of how I cured it

[67gtospud]

Originally Posted by Formulas

Plug reading without pictures

Basically you want gray white any color than pitch black about half way down the ground strap

Same with center electrode except at the tip and extended from the tip a bit

Basically hot enough to keep vicinity of the spark hot enough to burn off contamination off so it doesn't foul / fail to ignite

I'm gone for the weekend but will be home tomorrow afternoon. I'll post up a couple spark plug pictures then. I just changed them yesterday though they do have a fair bit of idle time on them shortly before I pulled them.

[67gtospud]

These are 2 of the plugs I pulled last week. Some are a little darker than these but most look similar. Again, there was quite a bit of idle time on these right before I pulled them

[steve25]

Your plugs and there heat range look fine to me!

[AG]

Heat range looks good but they look like you are rich.