Carburetor Idle Transition Slots

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threefortyduster

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St. Petersburg, FL
After getting to the bottom of the last issue, I yanked the carb off so I could reset it and go from there to make sure the idle is dead right next time.

When trying to set the idle transition slots to the .020", the primary went just fine.

However, I can have the secondary curb idle screw all the way off the adjuster to the point that there is over .020" between the curb idle screw and the shaft adjuster, and the secondary blades with a simulated return spring on the throttle lever expose over .047" of the transfer slot (my .024 and .023 feeler gauges stacked on top of each other). According to Demon (and Holley), this slot should be totally covered by the secondaries, but I just don't see how that can possibly happen when there is a throttle return spring on the carburetor.

Now..when I open the throttle, the blades do drop and cover the transition slot fully before reopening. Is this typical? I would like the car to idle somewhat correctly without having to buy a whole new carburetor.


Flickr album of the transition slots:
https://www.flickr.com/photos/67485541@N08/sets/72157652657512445

Video of the exact issue:
[ame]https://youtu.be/r-i0-HCyrmc[/ame]
 
If it's a 4 corner idle carb the back can uncover the idle slot also. You want the slots to be square give or take if it's a little more rectangle it's not the end of the world as long as your still on the idle circuit.
 
EL5DEMON340 said:
If it's a 4 corner idle carb the back can uncover the idle slot also. You want the slots to be square give or take if it's a little more rectangle it's not the end of the world as long as your still on the idle circuit.
Click to expand...

It is a 4 corner, it is a 650 cfm Speed Demon. Everything I see (and talking with Holley tech support today) they say the secondary idle slots should be invisible from the bottom. I'll probably just have to try it.
 
Try holding the carb up to a light. You'll be able to see if the primaries and secondaries are open about the same amount by how much light shines through.
 
Where did the initial timing end up?

You'll be chasing your tail if that's not sorted out first along with the vacuum leak. Putting the cart before the horse.
 
Some Holleys have a piece of linkage on the driver's side,, that is a positive secondary close, sometimes it needs a little bend to achieve total close..
 
crackedback said:
Where did the initial timing end up?

You'll be chasing your tail if that's not sorted out first along with the vacuum leak. Putting the cart before the horse.
Click to expand...

OP: Please do not ignore this!!!
 
crackedback said:
Where did the initial timing end up?

You'll be chasing your tail if that's not sorted out first along with the vacuum leak. Putting the cart before the horse.
Click to expand...

Yes I'm aware. The vacuum leak was below the carb, so the carb had to come off.

Before the carburetor goes back on the intake manifold for anything, it is going to be set the way the factory recommends it or until someone can tell me this situation is normal. Nothing from Holley or Demon shows that it is ok to have half the idle transition slot exposed.

As for timing, when the carb goes back on, I'm going to start with an initial 18 like you recommended, but I need to tune the distributor to only allow 16 degrees mechanical advance. I will probably just buy the Pertronix distributor because it has nice easy tabs that let you limit mechanical advance to to 16 degrees. (their tabs allow 12, 16, or 20).
 
threefortyduster said:
It is a 4 corner, it is a 650 cfm Speed Demon. Everything I see (and talking with Holley tech support today) they say the secondary idle slots should be invisible from the bottom. I'll probably just have to try it.
Click to expand...

Not sure they know what they are talking about. They can be opened up just like the primary. http://www.dragracermag.com/solve-idle-dilemmas-without-misusing-throttle-plat

Here is some good reading.

Have blades in the secondary been messed with that you can tell? You may be able to loosen them on the shaft and see if they close up more of the venturie. And make sure the venturie is clean so they can close all the way.

If you get your timing squared away it will help get your idle figured out.
 
I went and found some pix of the 650 Sped demon,, and it does in fact have the linkage I mentioned in Post 6,, if you haven't looked and checked it's operation to be sure it's not the cause,, frankly you're wasting our time and yours.. jmo
 
Am I seeing that video right?
When you first start to open the primary the secondaries close further before they start to open. It must be a problem with the linkage on the carb.
 
inertia said:
I went and found some pix of the 650 Sped demon,, and it does in fact have the linkage I mentioned in Post 6,, if you haven't looked and checked it's operation to be sure it's not the cause,, frankly you're wasting our time and yours.. jmo
Click to expand...

I will take a video of the linkage activation. I'm glad I can help you waste your time. That's pretty rude, jmo. If you don't want me wasting your time, feel free to not post in this thread.
 
threefortyduster said:
Yes you're seeing it right, hence the confusion.
Click to expand...
I believe that it is the link connecting the throttle shafts that is causing this. I witnessed this on a carb that I bent the link on to achieve full secondary opening. When the primaries were closed, the link was at the end of the slot and was pulling the secondaries open slightly . As the throttle was opened slightly, the secondaries closed. This is hard to explain but if you watch the linkage you will see what I'm talking about. This issue would probably only come up on a carb with the primary throttle plates closed a lot to attain a low idle speed , such as on a small stock or near stock engine. My particular case involved a 4777 650 dp on a stock 318.
 
forphorty said:
I believe that it is the link connecting the throttle shafts that is causing this. I witnessed this on a carb that I bent the link on to achieve full secondary opening. When the primaries were closed, the link was at the end of the slot and was pulling the secondaries open slightly . As the throttle was opened slightly, the secondaries closed. This is hard to explain but if you watch the linkage you will see what I'm talking about. This issue would probably only come up on a carb with the primary throttle plates closed a lot to attain a low idle speed , such as on a small stock or near stock engine. My particular case involved a 4777 650 dp on a stock 318.
Click to expand...

Thank you. How did you solve it? I'd rather the car not idle at 1500 or so if it can be avoided.

Did you just bend the linkage as the guy whose time I am wasting suggested or was there another way around it?
 
FBO Don used to help tune Demon carbs (Holley on steroids) and maintained the visible square transfer slots on a 4 corner idler. The adjuster for the secondaries is under the carb. Square them up, set fuel level and go from there. Your linkage may need a little adjustment.
 
threefortyduster said:
Thank you. How did you solve it? I'd rather the car not idle at 1500 or so if it can be avoided.

Did you just bend the linkage as the guy whose time I am wasting suggested or was there another way around it?
Click to expand...
I just removed some of the bend that I had put in it . The sec no longer opened quite all the way, but considering it was on a stock 318 with an LD4B
and headers, I didn't feel I needed every last CFM. When the car goes back together with a hotter motor I will fool with it some more.
 
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