Idle Transfer Slot on secondaries?

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340inabbody

340inabbody

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Posting here as I haven’t gotten much traction on FBBO.

Carb is a Holley 650 Double Pumper.

Does the idle circuit use the transfer slots on the secondary as well as the primary? Or are the secondary transfer slots for smoothing the transition from primary to secondaries?

Or another way to ask.

Do I need to have the transfer slots on the secondaries exposed the same way as on the primary side (just a small square)?

Thank you for taking the time to read and respond!
 
No. If you expose the transfer slots on the secondaries, you will probably increase the idle speed to 2500 RPM.
 
The way I have done it for 60 years (Right or Wrong) is
to have no transitional slots exposed.
.
If required, I drill small holes in the throttle plates
to get the idle high enough to tune with the Air Bleeds.

However, I deal with very radical engines with very little vacuum
signal.
 
340inabbody said:
Posting here as I haven’t gotten much traction on FBBO.

Carb is a Holley 650 Double Pumper.

Does the idle circuit use the transfer slots on the secondary as well as the primary? Or are the secondary transfer slots for smoothing the transition from primary to secondaries?

Or another way to ask.

Do I need to have the transfer slots on the secondaries exposed the same way as on the primary side (just a small square)?

Thank you for taking the time to read and respond!
Click to expand...
In most cases the transfer slot on the secondary's are usually shorter and higher. To get the so called small square window on the secondary's would require you to open them too far allowing too much are in and raising the idle speed.
 
mbaird said:
It’s a custom carb so it has aftermarket.
I only pointed this out in case readers know that not all Holley looking carbs follow this procedure.
Click to expand...
In most cases the aftermarket transfer slots are too big and need TSR to get them right or as some one I know who knows more about this stuff said he just rips them off and puts the OEM holley base plates back on.
 
The reason I am asking is that I am finding that the idle mixtures are having a negligible effect with vacuum/idle. I assumed the transition slots were opened too far. It’s not see pic.

Also Idle needs to be 1100RPM in Park and drops to 850RPM in gear. I don’t want to start drilling if this isn’t the issue but it still appears to want more air? I have no adjustable air bleeds.

Would my next step be drilling out the air bleeds and putting in metering screws? I don’t really know where to go from here….

IMG_3415.jpeg
 
Hysteric said:
Once they are set up correctly you can get them to where they only drop 50 RPM


Change that. What are the IAB's and IFR'S
Click to expand...
They must be stock as I haven’t touched them. Are they not fixed brass inserts? This is my first Holley.

image.jpg
 
Describe your engine build and tune . May be a-timing issue as well . Or power valve or float height or fuel pressure .
 
Fuel pressure @6.5, floats adjusted at bottom of window requiring bumping the car to slosh out. Timing is now fully adjustable on the fly as I am running the Progression Distributor. 18° at idle.
Motor is solid flat tappet lifter J heads with double springs. Unknown cam. Pistons 12:1 TRW. Duel plane AL intake.
Note had colder plugs to help with minor detonation and a slow curve all in 32° at 3000. The plugs are now fouled and I need to go hotter than the Autolite 63’s that are in there. Need to probably go back to the Autolite 65’s?

image.jpg
 
That idle is quite high. What's the cam specs and how much vacuum is it making at 850?

What's the jetting?
 
Do we assume you've adjusted the secondaries so they feed some air at idle?
This quite often allows you to close the primaries enough to get a clean idle with both mixture screws.
It usually doesn't take much of an increase to allow this to work.
 
Hysteric said:
That idle is quite high. What's the cam specs and how much vacuum is it making at 850?

What's the jetting?
Click to expand...
Idle is too high in N. It drips from 1100 to 850 in gear. That’s an issue. Unknown cam but I believe it has a significant overlap. Vacuum is about 11Hg at idle. Goes up as timing increases.
 
sccachallenger said:
Do we assume you've adjusted the secondaries so they feed some air at idle?
This quite often allows you to close the primaries enough to get a clean idle with both mixture screws.
It usually doesn't take much of an increase to allow this to work.
Click to expand...
Right. That's a good trick, too. But, SO FAR I haven't seen one where you have to expose any of the transfer slot on the secondary side. They are just too high up to do that. Heck, I had mine on my 450 adjusted square on all FOUR when I fired off my slant 6 to break in the cam. It popped right off.......at about 2700 RPM. lol I just left it there and it broke in fine. I readjusted it back later.
 
340inabbody said:
Idle is too high in N. It drips from 1100 to 850 in gear. That’s an issue. Unknown cam but I believe it has a significant overlap. Vacuum is about 11Hg at idle. Goes up as timing increases.
Click to expand...
Pull initial timing in until the vacuum stops climbing. See how it does then.
 
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