Holley Idle Transfer Slots

I've pulled my Holley Ultra HP (double pumper) apart for a good clean and 'reset to factory specs' ahead of some fine tuning. I want to start with the absolute basics and proceed from there.

Question on the transfer slots, before I begin playing with the idle settings. Endless tech articles suggest aiming for just enough slot to be exposed under the throttle plate, that it forms a 'square' shape. Any more than this is not a good thing.

I picked up a Holley 600 off Craigslist and the guy said he had it on his car for 10 minutes and it was too much carb for his car. Needless to say I got a good deal on it and a man can't have to many carbs in my opinion. I pulled the bowls off and everything looked clean so I checked the transfer slots and idle screws and put it on. Adjusting the pri throttle blades so.020' of the transfer slot (looks like a square as seen with the carb upside down) is a Barry Grant thing not Holley but is an ok starting point. It insures the transfer slot is not completely uncovered. I believe Holley sends them out new in the box with about.030' or.040' uncovered. I got it all back together over the weekend. I need to pull the carburetor back off and readjust the secondary throttle plates, i couldnt get it to idle happily under 1500 rpm, pulling 13 inches of vacuum. I have too much transfer slot showing on the secondaries, i was able to shut the primary throttle blades all the way and still have the car. The adjustment is made using the Idle speed Screw on the side where the Throttle linkage hooks up. Turn the Carb over and slowly back off the Idle screw until the Transfer slot BELOW the Throttle Plate looks like a Square. You do need to be sure the Choke fast Idle screw is off and not holding the Throttle plate open. By Joe-JDC - 3 Years Ago. On a Holley you set the idle mixture for most vacuum then go back in about 1/8 turn. Adjust the desired idle with the throttle adjustment screw (there goes how far the transfer slot is un-covered). Like I said earlier about your bog or stumble, my money is on the accl pump, pump cam and squirter size needing a bit of tuning.

But what about less? My primaries are covering the slots (only just) - I can almost just see the very tip of the slot. So I would actually need to open them more to achieve a square. Not what I was expecting, especially since my carb has a history of being filthy rich.

My secondaries are also fully covering the slots - even more-so than the primaries. I'd need to give the the base idle screw a really decent turn to expose the transfer slot and form a square.

Holley Idle Transfer Slot Tuning

So how important is the square? Am I best opening both primary and secondary throttle positions to have matching squares, or just leave them alone (what we'll call fully seated) - and then adjust idle accordingly. Holley's instructions specifically state the the throttle blades should not be touched as they are already optimised from factory. Hence I find these 2 different things quite contradictory...

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PostPosted: Sat Mar 01, 2008 8:05 am

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Thanks guys!
I will up grade from the dual resistor to a single and hopefully find one with a little lower ohm rating.
This is my situation:
During the winter months with the lights on, wiper on and blower on high the voltage stays kind of low at 600 rpm and will cause a very small stumble if I take off slowly. If I hit the pedal aggressively there is no stumble but the car wants to go sideways with the posi. So I would like to see at least 6 volts at the coil not 3 or 4 in those conditions. I would like a little more voltage for a nice smooth acceleration. After recurving the distributor the throttle is allot more sensitive and responsive making the car allot more touchy.

Your idle circuit may be lean. Do this check: raise the idle speed up to about 1400 RPM. Look into the carb to make sure no fuel is coming out of the booster venturis. If it is, lower engine speed until fuel no longer flows out of boosters. Then turn idle mixture screw in (out if reverse idle circuit). If engine speed increases, then your idle circuit is lean. If opposite is true, then idle circuit is rich - not likely. If lean, then the correct fix is to enlarge the idle feed restriction. If all checks out OK, then go ahead and play with your ignition.
Mitch

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PostPosted: Sat Mar 01, 2008 8:32 am

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if idle is indeed rich @ 600 rpm but you get stumble on light throttle action, maybe your idle trasnfer slot is either partially clogged or lean for your motor. that is assuming your accel pump is working flawlessly. the drawback if your transfer slot is lean, is that it uses the same circuit as idle. You'll have to rework the slot.

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PostPosted: Sat Mar 01, 2008 9:18 am

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Juan,
Setting aside the low voltage issue at the coil under severe load.
My accelerator pump shot is awesome. That is why the rear end will break loose very easily if you hammer the throttle. The gentle take off is what I am going for.
Since this is a 1920 Holley Economiser, how would you suggest reworking the slot?

the drawback if your transfer slot is lean, is that it uses the same circuit as idle. You'll have to rework the slot.

I am interested in giving this a try over the weekend. My idle mixture screw has a very subtle effect and have suspected that the idle bleed may be on the small side.

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PostPosted: Sat Mar 01, 2008 9:33 am

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Juan,
Since this is a 1920 Holley Economiser, how would you suggest reworking the slot?

the drawback if your transfer slot is lean, is that it uses the same circuit as idle. You'll have to rework the slot.

I am interested in giving this a try over the weekend. My idle mixture screw has a very subtle effect and have suspected that the idle bleed may be on the small side.

Ted, the idle transfer slot and the idle air bleeds are 'engineered' into the carb. The only variables you can change are the throttle plate position relative to the transfer slot and the idle feed restriction. Both affect fuel delivery and transition into the main circuit. From your description of the idle screw's lack of sensitivity, I am guessing that your idle circuit is lean. This means you will lean out as you open the throttle during idle to main circuit transition. Do the test I suggested. It is easy and will tell you what is going on.
Does your carb have a reverse idle circuit? At idle, can you richen the mixture enough to cause a drop in engine speed? How far do you have to turn the screw before you see a response. Being an Economaster, the idle circuit is probably setup on the lean side.
Mitch

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PostPosted: Sat Mar 01, 2008 11:16 am

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the drawback if your transfer slot is lean, is that it uses the same circuit as idle. You'll have to rework the slot.

I am interested in giving this a try over the weekend. My idle mixture screw has a very subtle effect and have suspected that the idle bleed may be on the small side.

on the base, right below the idle transfer slot, there's a brass plug. You have to pop this circuit open to work there. A lot of folks don't like to mess with a carburetor beyond swapping jets (PowValve in your carburetor ain't a variable as they did come and come in only one flavor)
but if we think of economaster as holley did, a more precise fuel metering system carb than their regular production, some things may be an issue.
Idle, and transfer slot are the first. Let me elaborate. Those carburetors are meant for a bone stock slant six of the gas concern era. the accel pump shooters are smaller than regular 1920's, that is because the annular finned booster gives them excellent signal features (crisper throttle response, more fuel drawn with smaller jets, etc) so when you kinda mash it, your improved slant takes advantage of that. But in the transition, you're stuck with 'barely enough' for meeting strict emissions controls plus for a motor that was intended for economy or 'granny' driving.
Now, using a drill bit, we can get a measure of the idle air bleed. I kinda refuse to believe your idle circuit is rich, how many turns you have left in the idle screw when you kill the engine? if you can screw it all the way in and the engine will idle roughly then yes, you have a idle/accel pump/transfer slot circuit problem (all those subcircuits 'drinks' from the same well)
Plus if I don't recall wrong, by the time economaster holleys were on the market, the timing specs for the slant six was about zero initial advance. Increased advance creates sorta 'artificially lean' condition. I believe you have reworked your timing curve, am I wrong??
I would check if your idle circuit and its branches ain't lean as MitchB suggest, before getting serious hands on approach on the matter. How? just put a piece of small wire inside the idle air bleed (peel any multifilament wire and grab 3 or 4 'straws' and tie the other end to anything so if they fall your engine would not suck them.

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PostPosted: Sat Mar 01, 2008 1:43 pm

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8< 8= 8< 8= 8< 8= 8< 8=
(much good information)
8< 8= 8< 8= 8< 8= 8< 8=

if I don't recall wrong, by the time economaster holleys were on the market, the timing specs for the slant six was about zero initial advance.

0Â° (TDC) was the spec from around '72 through '75 or so (years not exact, don't have specs in front of me). Starting in '76 and up through the end, the spec was for a lot of initial advance...between 8Â° and 12Â°.

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PostPosted: Sun Mar 02, 2008 4:59 pm

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Mitch and Juan,
Thank for the detailed advise. It rained and hailed all day yesterday. Today we have some sun, so I installed an electric fan and did the carb testing.
Mitch,
Per your instructions I raised the idle to 1400, no fuel from booster, screwed the idle mixture screw in and the idle speed slowly reduced till it quit at 1.5 turns out. It seems to run best at 4.5 turns out with 12 degrees of initial timing. Turning the screw out much more and you can here the idle slow down again getting rougher and you can smell it at the exhaust pipe as being too rich.
Juan,
My carb does not have a reverse idle circuit. Screw the idle mixture screw in to lean it out. Turn it out to richen it up. It has a very subtle change, not a sudden change like on a Rochester.
I grabbed some .010 monel steel fishing leader and ran 3 strands down the idle air vent and there was no significant change.
Yes, I recurved the distributor. It shows 30 degrees at 2000 rpm.
The pump shot is sudden and responsive. With more timing, it responds crisper. 16 degrees is nice, 20 degrees is awesome. Super instantaneous revs. 12 degrees is much tamer so I am not freeking my wife out. At cruise with 12 degrees it doesn't surge like it does at 16 or 20 degrees initial. It must be putting me over the top when I let off on the gas at the higher settings. I have a 11R vacuum pod. The mechanical is about 18 degrees, a little more at 2500.
If you could explain how to get rid of the slight sag or bog after decelerating or starting up from a stop, with light pedal pressure that would be great!
As I said before, if I aggressive mash the throttle, there is no bog, it just jumps, or goes sideways.
Thanks guys,
Ted

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PostPosted: Sun Mar 02, 2008 5:24 pm

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hey ted
never thought you had a reverse idle screw (there's no such thing as that on a 1920)
can you kill the engine at idle by screwing the idle mixture screw all the way in? (it should die at about 1 turn of fully closed)
I'd try 2 things: 1st, actually reducing the jet on your carb. Yes, going down to a 55 and see what happens. If this improves your light throttle pressure bog condition but hurts power and surges on cruising, I'd then ream the idle air bleed and go back to a 57 jet. Follow?

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PostPosted: Sun Mar 02, 2008 8:37 pm

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Juan,
Yes, I follow.....and yes it will die at about 1 turn at idle which is about 350 rpm.
If we get some good weather this week I will pop in a 55 jet and give it a try. I know the smaller jets always seem to be crisper, but forces me to run on the power valve more than I would like. Mine is a dual plunger type and it dumps allot of fuel and goes! I have allot of hills around here and need a good compromise on the main jet.
Are you referring to idle bleed on the top, when looking down the throat of the carb from the air cleaner side where you had me run the wire in?
On opening up the air bleed, what drill bit size would you try?
Any idea what the stock idle bleed hole diameter might be?
I just had the car out tonight and it runs nice and warm now with the new electric fan set up.. It used to run a little on the cold side with the clutch fan churning all the time. I noticed that the bog is not quite as bad when it's good an warm. Pretty smooth......but when it's cold and choke is off, in the in-between stage the bog is very evident.
This is super info.......thanks!

Last edited by Aggressive Ted on Sun Mar 02, 2008 8:55 pm, edited 1 time in total.

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PostPosted: Sun Mar 02, 2008 8:52 pm

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Eric W,
Good ideas!
I checked my dual resistor ohm rating and it is 1.5 ohms. I went to our local Napa and checked the new style single resistor (back is not potted) and they measured 2.5 ohms. Then I had them pull out some early single resistors that are triangle shaped and potted and they all measured 1.5 ohms.
I pulled out the big MSD resistor that came with the MSD Blaster 2 coil and it reads 1 ohm but is stamped .85 ohms.
Next weekend I will cut the old dual connectors off and solder up new crimp ends and install the MSD resistor and then measure the voltage at the coil. That mod should give me a little more voltage at idle. Good idea!
When you run a wire from the alternator to the battery solenoid doesn't that throw off the amp meter to where it will not show discharge or charge? Isn't that bypassing it? or do you still see activity on the amp gauge?
Thanks,

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PostPosted: Sun Mar 02, 2008 11:30 pm

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Yeah, the ammeter isn't accurate anymore. Mine reads just below the middle at idle with nothing on. Your not bypassing the guage, you still get power through the system. Your just giving a more direct route from the alt to the battery. Not as much drain when you have the lights, wipers and defrost going when sitting at that long light with your turn signal on.

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Idle bleed for a stock 1920 would be in the 1.5 mm ballpark. I would really advise against drillbits, I'd rather use a hex reamer, like a broach.
You did put the wire on the 'big hole' air bleed didn't you? the one that would be near the valve cover? I'd rather play a lot with jets before reaming idle air bleed.
One thing that puzzles me is this. Assume we put a smaller jet. Throttle response at medium/wide openings wouldn't be compromised because economasters have great signal with their fancy finned annular boosters, power valve would kick in more often on light/medium openings over load situations,... you can always customize the power valve rating by cutting the spring one or two loops at a time (no need to tear appart the whole thing, just drop the air cleaner, those 3 screws and bingo....) and you could run wider open idle screw settings (remember, transfer slot uses the same circuit) ...
I read that you have full 12v at ignition on motor off... and resistor when you're running on the motor? that should be the exact opposite way! I'm sure dan will fill in here, but you sould be getting 12v on engine running. Wich side of the car is the looped double contactor for the resistor is fitted over? (you know, there's a short wire going from one terminal to another on one side of the double resistor) it should be on the passg side of the car, looking at it from the front of the engine bay.
Inspect the idle transfer slot, check for debris, casting flaws, etc. Close the idle screw all the way in and using a good carb cleaner or WD40 give it a good pressurized shot (easy using them straws) then open almost all the hay out and shoot another time (thru the idle air bleed) then use compressed air to clean the whole circuit. (This better done with carb of the car, I know you get it but never hurts to add to the instructions sheet just in case a newbie reads and coopycats )

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PostPosted: Mon Mar 03, 2008 8:31 am

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Per your instructions I raised the idle to 1400, no fuel from booster, screwed the idle mixture screw in and the idle speed slowly reduced till it quit at 1.5 turns out. It seems to run best at 4.5 turns out with 12 degrees of initial timing. Turning the screw out much more and you can here the idle slow down again getting rougher and you can smell it at the exhaust pipe as being too rich.
Ted

At normal idle speed, do you get a best idle with the idle mixture screw turned 4.5 turns out or was this different? We want to see if turning the idle screw in or out at 1400 raises the engine speed. In other words, does adding or pulling fuel at 1400 compared to your idle setting change anything?
Mitch

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PostPosted: Mon Mar 03, 2008 9:12 am

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Mitch,
At idle or 1400 there just isn't any significant difference. I also tried it at 1200 to be sure. 4.5 turns just seems to be a happy place, not super lean causing the idle to decrease or super fat causing the idle to decrease from loading up. This particular Economaster carb doesn't respond as fast to idle screw adjustments as a stock 'T' bar type 1920 with a #58 jet. It might be due to the #59 jet that I put in it last week to cover up the bog. But with a fatter jet, if the manifold is not super hot, it still bogs, so I am going back to my trusty #57. I also lost 2 miles per gallon (20.5 mpg) by going to the #59. I was getting 22.5 mpg with the #57. I have been driving the car hard and fast lately. It get's 24.5 mpg if I drive like a granny. That means I can't cruise at 70 mph on the freeway and pass too many cars on the back roads.
Juan wanted me to try the #55, so I need to give that a try as well and document the results.

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PostPosted: Mon Mar 03, 2008 9:52 am

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Juan,

You did put the wire on the 'big hole' air bleed didn't you? the one that would be near the valve cover? I'd rather play a lot with jets before reaming idle air bleed.

Yes!

you can always customize the power valve rating by cutting the spring one or two loops at a time (no need to tear appart the whole thing, just drop the air cleaner, those 3 screws and bingo....) and you could run wider open idle screw settings

That is a heck of a good idea to modify the power valve. Hadn't thought of that one. I could carry a few extra power valves for different set ups. Right now the stock one kicks in at 10' on the vacuum gauge. It would be nice to post pone that to say 5 or 6'.

I read that you have full 12v at ignition on motor

That is on my gauge inside when everything is on, fully loaded system.
I was taking measurements at the coil seeing 4.5 volts at idle no load. Lower voltage with everything on, 3.5 to 3.8 volts. Thus thinking the lower voltage was causing the bog.

Which side of the car is the looped double contactor for the resistor is fitted over? (you know, there's a short wire going from one terminal to another on one side of the double resistor) it should be on the passg side of the car, looking at it from the front of the engine bay.

Yes, it is on the left side/passenger side. I see about 13.6 volts up there, no load at idle.

Inspect the idle transfer slot, check for debris, casting flaws, etc. Close the idle screw all the way in and using a good carb cleaner or WD40 give it a good pressurized shot (easy using them straws) then open almost all the hay out and shoot another time (thru the idle air bleed) then use compressed air to clean the whole circuit.

I have done this before about a month ago when the carb was off, but I will give it another shot for good measure, but leaving it on the car this time.

I'd try 2 things: 1st, actually reducing the jet on your carb. Yes, going down to a 55 and see what happens. If this improves your light throttle pressure bog condition but hurts power and surges on cruising, I'd then ream the idle air bleed and go back to a 57 jet. Follow?

I have yet to try a #55. Last time I did was about 3 months ago and yes it was very crisp, no bog, but no power when you needed it either. It would go on the power valve way too often..... but it was a nice crisp feel at low loads, just no power when you came to a hill until the power valve dumps.
It is a very anemic feel as far as over all feel. A # 57 is a good compromise. A #58 is very nice!. The #59 is just fat and alot of fun.
Guess I need a four barrel so I can run it lean, better tune the power valve and have the secondaries for passing.
Thanks guys for the input!
If this Economaster can be tuned just a little to improve that off idle lean transition when using a light foot (little pump shot) that would be great. Right now the only way around it is to aggressive mash the throttle so the pump shot is longer which eliminates the bog. I am not always in the mood to do drive aggressively

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