Divorced idle circuits

[statsystems]

These blind men of Carburetorstan
Disputing loud and long,
Each in his own opinion
Exceeding stiff and strong,
Though each was partly in the right,
And all were in the wrong!

As they'be been groping 'round the Elephant
They must have no sense of smell,
Lest they'd know what they've been stepping in
As this thread has gone so well.

There is something in the Gasoline
In Carburetorstan,
That makes every Carburetor Man
Think he is the one to understand.


OP, did you get some clues from all this or would you still like to have any of your original questions answered?

Set that poem to rap music and you'll be a kajillionair.

I'd like to have the OP questions answered because I'm curious as well.

[NormS]

You see , Malik,you're doing the same thing again. Read what you just said.

"Wow ... defensive comprehension at its best.
That merely exclaims that the way you described is not the only way it can be done because, you possibly have never done anything else as that and better fuel control can be had.
A bit "tongue in cheek" perhaps but, from all your following posts, that appears it might have been correct.
Says absolutely nothing about any other way being the ONLY way."

Again, you're attacking me and inferring that I speak from inexperience. You're accusing me of doing exactly what you are doing. I never said my way is the only way to do it. I said, the way I do it, is the way that gives me the best results. I tried what you say is the better way, and found it gave results that left something to be desired.

[n2xlr8n]

These blind men of Carburetorstan
Disputing loud and long,
Each in his own opinion
Exceeding stiff and strong,
Though each was partly in the right,
And all were in the wrong!

As they'be been groping 'round the Elephant
They must have no sense of smell,
Lest they'd know what they've been stepping in
As this thread has gone so well.

There is something in the Gasoline
In Carburetorstan,
That makes every Carburetor Man
Think he is the one to understand.


OP, did you get some clues from all this or would you still like to have any of your original questions answered?

Set that poem to rap music and you'll be a kajillionair.

I'd like to have the OP questions answered because I'm curious as well.

I'm with Stat- let's hear what swami Tuner says; I've always loved his carb posts.

[Walter R. Malik]

I remember divorced idle circuits being talked about a while back here on Speedtalk. So i have some questions to be answered please.
1. On a race quality 4150 platform WHAT is the definition of divorced idle circuits ? 2. What was the reason for developing this feature ?
3. In what application (type of service, racing, driving, etc.) would divorced idle circuits be most likely employed ?
4. What are the good traits of divorced idle circuits ?
5. Are there ANY negative aspects to D.I.C.'s ?

Thanks in advance for any and all responses ! Mark H.

1. has been answered in a lot of posts in this thread
2. The main reason it was used is for better fuel control at closed throttle without affecting the off idle, transition.
3. Applications where the engine spends a lot of time on deceleration at closed throttle; mostly low emission road vehicles.
4. Less fuel consumption, less hydrocarbon in the exhaust gasses.
5. The difficulty within its complexity for getting it to do exactly what it is intended to do in use.

[jmarkaudio]

This is the latest metering block to use a divorced idle. I think it was intended for the new Gen 3 large bore carbs, still a bad idea and doesn't run well. I've also found them on a pair of Gen 3 1050's on a nitrous engine, same issue there as well. The first two pics show the entrance point to the idle/transition fuel.



This leads to the vertical idle well towards the idle jet, located at the top where I don't want it.



This is the area I mill a slot to change it to a mainwell fed idle, plug the bowl side of the entrance and drill at an angle a passage to the mainwell. It gets threaded for a lower idle feed.


This is a Pro Stock metering block, also was a divorced idle. You can see the passage I milled to feed it from the mainwell.



I've done this to several carbs, all suffered from poor idle and transition quality, this and an overabundance of emulsion made the fuel curve erratic and lean at the top, distribution was impossible to fix. So many builders don't realize how bad the carbs run overall when you don't pay attention to low speed metering.

[Walter R. Malik]

This is the latest metering block to use a divorced idle. I think it was intended for the new Gen 3 large bore carbs, still a bad idea and doesn't run well. I've also found them on a pair of Gen 3 1050's on a nitrous engine, same issue there as well. The first two pics show the entrance point to the idle/transition fuel.

With the first blocks you show, it looks like they are actually referring to this incorrectly, (as you say), the idle AND transition fuel are both divorced from the main-well.
With an actual divorced idle system, the transition slot draws its fuel from the main-well while only curb idle fuel is completely separated.

I do agree that these compound divorced systems don't transition very well.

I am only guessing but, I believe the thought here was that the intermediate system would "fill-in" the bad tip-in so the idle and transition could remain very lean. A bad idea in my opinion.

[swampbuggy]

Hey Mark W., i noticed how those main jets are made. That makes good sense, do you always use that style in your carb builds ? Mark H.

[jmarkaudio]

Those are BLP jets, I use that in almost everything. They are numbered in .001 increments so smaller changes can be made if needed.

[groberts101]

I keep snickering because every time I look at Marks pictures I want to say.. "man those metering blocks look tiny against your huge hairy thumbs!". But I won't.. because that would just be too juvenile.

[Tuner]

I keep snickering because every time I look at Marks pictures I want to say.. "man those metering blocks look tiny against your huge hairy thumbs!". But I won't.. because that would just be too juvenile.

You shave your legs, do ya?

[fordman460]

groberts thanks for that. Was trying to put that into words myself! But unlike Tuner, I don't want to know if you shave your legs... or thumbs.