Holley Idle Transfer Slots

Page 1 of 10

[ 141 posts ]

Go to page12345 … 10Next

I found this out on the net but conflicts with other things I've read. 'The next thing to note is that the secondary transition slots on a Holley are often located higher in the throttle bores than on the primary side: If you try to obtain the.020” transition exposure on the secondary side of a Holley, you will often end up with the secondaries opened significantly more than the primaries. The ideal position of the throttle blades in relation to the idle transfer slot is shown in Photo A where the primary throttle blades just barely uncover the bottom of the transfer slot-roughly. I just read in an old Holley manual that the transfer slot circuit can be tested. 'Slowly opening the throttle with the idle speed screw until the booster starts supplying fuel, then backing off until it just stops. If richening or leaning with the idle mixture screw causes rpm drop off, the mixture is correct. I noticed when I rebuilt my Holley that my idle transfer slots were uncovered quite a bit. I have a pretty healthy cam and a single plane intake and I've read my problem is pretty common. I also installed a 5.5 powervalve to replace the 6.5 since my vacuum is around 10-11. To improve fine tuning abilities I installed an aftermarket bracket on the secondary throttle shaft of my 850 CFM Holley dual-feed double-pumper with mechani.

Print view

Previous topic Next topic

Author

Message

PostPosted: Sat Mar 01, 2008 8:05 am

Offline

Board Sponsor

Joined: Fri Nov 01, 2002 11:04 am
Posts: 270
Location: New York
Car Model:

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

Top

PostPosted: Sat Mar 01, 2008 8:32 am

Offline

Board Sponsor

Joined: Mon Jan 12, 2004 4:20 am
Posts: 2011
Location: Argentina
Car Model:

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.

_________________
Juan Ignacio Caino
Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Top

PostPosted: Sat Mar 01, 2008 9:18 am

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

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.

_________________
Aggressive Ted
http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger
74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5' HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26' tires, 25+MPG

Top

PostPosted: Sat Mar 01, 2008 9:33 am

Offline

Board Sponsor

Joined: Fri Nov 01, 2002 11:04 am
Posts: 270
Location: New York
Car Model:

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

Top

PostPosted: Sat Mar 01, 2008 11:16 am

Offline

Board Sponsor

Joined: Mon Jan 12, 2004 4:20 am
Posts: 2011
Location: Argentina
Car Model:

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.

_________________
Juan Ignacio Caino
Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Top

PostPosted: Sat Mar 01, 2008 1:43 pm

Offline

Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
Posts: 23548
Location: North America
Car Model:

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°.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Top

PostPosted: Sun Mar 02, 2008 4:59 pm

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

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

Top

PostPosted: Sun Mar 02, 2008 5:24 pm

Offline

Board Sponsor

Joined: Mon Jan 12, 2004 4:20 am
Posts: 2011
Location: Argentina
Car Model:

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?

_________________
Juan Ignacio Caino
Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Top

PostPosted: Sun Mar 02, 2008 8:37 pm

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

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.

Top

PostPosted: Sun Mar 02, 2008 8:52 pm

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

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,

Top

PostPosted: Sun Mar 02, 2008 11:30 pm

Offline

Turbo EFI

Joined: Sun Nov 03, 2002 1:49 pm
Posts: 2445
Location: Lubbock, TX
Car Model:

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.

Top

Post subject:

Offline

Board Sponsor

Joined: Mon Jan 12, 2004 4:20 am
Posts: 2011
Location: Argentina
Car Model:

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 )

_________________
Juan Ignacio Caino
Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Top

PostPosted: Mon Mar 03, 2008 8:31 am

Offline

Board Sponsor

Joined: Fri Nov 01, 2002 11:04 am
Posts: 270
Location: New York
Car Model:

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

Top

PostPosted: Mon Mar 03, 2008 9:12 am

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

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.

Top

PostPosted: Mon Mar 03, 2008 9:52 am

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

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

Top

Page 1 of 10

[ 141 posts ]

Go to page12345 … 10Next

Page 4 of 10

[ 141 posts ]

Go to pagePrevious123456 … 10Next

Print view

Previous topic Next topic

Author

Message

PostPosted: Thu Apr 10, 2008 8:32 pm

Offline

Board Sponsor

Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9679
Location: Salem, OR
Car Model:

so noone would be forced to use a BBS again

I just took apart a BBS and the Bendix/Stromberg carb and I can see where these have the advantage over the holleys (the BBS is fully disassemblable and has no blind passages/sealed metering block)... The stromberg is even more simple and it looks like it was designed to be able to knock the main venturi out and change it and increase the CFM rating with no major hassle... too bad there's not a kit with these major assembly parts in it...
LOL...
-D.Idiot

Top

PostPosted: Fri Apr 11, 2008 2:06 pm

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

SlantSixDan wrote:
What-all kinds of info are we after for background/carb selection?

Juan wrote:
bleeds/jets sizes according to years, accel pump discharge hole size. venturi and throat sizes, etc. also P/N for chrysler specific applications.

SL6Dan,
Could you help us out?
Thank you for looking up the specs.

Top

PostPosted: Tue Apr 15, 2008 5:10 am

Offline

Board Sponsor

Joined: Mon Jan 12, 2004 4:20 am
Posts: 2011
Location: Argentina
Car Model:

so noone would be forced to use a BBS again

holley 1920 ain't the best one barrel around, is just the one maker that casted one barrels for more time and the parts avalibility kicks ass around the world. Go try'n find a needle for any carter carburetor outside the states and say 3 or 4 more countries: you're screwed up! the stromberg carb is WAY better than BBS's and Holleys. Now that I think about it, I've seen a lot of US made 1 barrel holleys with the detachable steel throttle base (that will be like you say about the BBS, fully accesible passages and such)
Anyway ain't a big dealie to pop some plugs, clean and repop close on a 1920... I'm amazed at how guys wich such an experience in fiddling with way more complicated mechanich issues frown their foreheads when it's time for poppin' and cleanin metering blocks and carbs.

_________________
Juan Ignacio Caino
Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Top

PostPosted: Tue Apr 15, 2008 9:41 am

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

Top

PostPosted: Tue Apr 15, 2008 10:41 am

Offline

Turbo EFI

Joined: Sun Nov 03, 2002 1:49 pm
Posts: 2445
Location: Lubbock, TX
Car Model:

If possible, it would be nice to see some pictures of these modifications on the 1920's. You know, what plugs to pull, what to do once they are out, etc.

Top

Post subject:

Offline

Board Sponsor & SL6 Racer

Joined: Sun Jul 30, 2006 8:36 pm
Posts: 2432
Location: East Arkansas
Car Model:

I agree. It would be nice to See some of this. Guys You are doing a Great Job with this thread. THANKS
Frank

_________________
Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178' FED
82 D150
All Slant powered

Top

PostPosted: Mon May 19, 2008 9:48 am

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

Juan,
I had the Economaster off this past weekend and drilled the potted over idle bleed hole with a #65 drill bit.
When I fired it up my normal 750 rpm idle went to 400 rpm. Now you can hear the transfer slot working very easily. It sounds like a huge water large water fall in there. I was running with the idle mixture screw at 5.5 turns and I roughly set it at 2.5 turns. It sounds and feels good cold no bog, but after driving 70 miles this morning to work, it was very warm and acted very differently. It feels like a hicup or very slight bog. It may still be too rich. I am thinking I need to open the hole up a little more? or lean out the idle mixture screw some more.
I am not quite sure yet. The throttle is way more responsive now and hard to hold still. Any slight pressure change on the gas pedal makes the car respond right away. I am having to learn how to drive all over again. That little change made a huge difference in the way the engine responds.
I will play with it on the way home tonight to see what it wants.

Top

PostPosted: Mon May 19, 2008 10:23 am

Offline

Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
Posts: 23548
Location: North America
Car Model:

H'mmmm. You may want to try drilling a vacuum calibration hole:
This hole is for calibration of the power valve and vacuum advance. Some carburetors have it and others don't, but once it's there if you don't want it any more it's easy to plug...

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Top

PostPosted: Mon May 19, 2008 10:32 am

Offline

Turbo EFI

Joined: Sun Nov 03, 2002 1:49 pm
Posts: 2445
Location: Lubbock, TX
Car Model:

Ted, I've found that turning that little screw even a little has big effects on idle and throttle response. My engine still has kind of an uneven idle, but it seems like it wants to run all day at 70+ with no problems. It also pings slightly on steep hills now...though it dosn't on long freeway grades at speed. Maybe time to futz around with the distributer springs again....

Top

Post subject:

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

Eric,
I have noticed the same thing that the idle air bleed has a huge! effect on idle quality. This Economaster carb I have (12R-7610 for 1968-72) has never had a normal idle mixture screw setting. It has always been very fat 5 or more turns to get it to idle smoothly because the idle air bleed was potted over.
Opening it up with the #65 drill really kicked the emulsion circuit in gear.
That little brass screw your adjusting is the idle air bleed adjuster. I am not sure yet where it should be set. All I know is that by opening it up some with the .035 #65 drill has made it run richer. Need to figure out the next tuning steps...............
I will take a picture tonight of the brass adjuster and send it to Dan.
What size main jet are you using now?

Top

PostPosted: Tue May 20, 2008 1:03 am

Offline

Turbo EFI

Joined: Sun Nov 03, 2002 1:49 pm
Posts: 2445
Location: Lubbock, TX
Car Model:

What size main jet are you using now?

A #58.

Top

Post subject:

Offline

Supercharged

Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model:

Eric,
I sent the pics to Dan last night. He should give us a heads up soon on the brass idle air bleed screw. On all the 1920 carbs I have, there seems to be a large well at the top, but in all reality you can't push any wire or drill bit in the idle air bleed location. It seems that Holley has plugged them off.
Now that I have opened up the idle air bleed Juan is suggesting that I try going up two sizes on the jet to balance everything out. If it isn't raining too hard tonight, I will pop in a #60 and see what happens.

Top

PostPosted: Tue May 20, 2008 9:47 am

Offline

Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
Posts: 23548
Location: North America
Car Model:

Yup, I definitely think this screw you're showing me is the Holley 1920 version of the Carter BBS factory-adjustable idle air bypass, not originally intended for field adjustment and so plugged off after adjustment on the production line.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Top