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.
Holley Idle Transfer Slot Restrictor
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.
When you convert to 4-corner idle, you should be blocking the passage to the transfer slots. All of the idle fuel should be going through your new mixture passage. Then, you can set your throttle blades wherever you need them. This uncovers the idle transfer slot, which can cause off-idle stumble problems. The only way to spot this problem is to remove the carburetor and see if the throttle blades uncover more than 0. 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.
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.
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: Thu Apr 10, 2008 8:32 pm |
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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
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PostPosted: Fri Apr 11, 2008 2:06 pm |
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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.
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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
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PostPosted: Tue Apr 15, 2008 5:10 am |
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Joined: Mon Jan 12, 2004 4:20 am
Posts: 2011
Location: Argentina
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 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.
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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.
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PostPosted: Tue Apr 15, 2008 9:41 am |
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Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model: |
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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
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PostPosted: Tue Apr 15, 2008 10:41 am |
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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.
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| 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
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PostPosted: Mon May 19, 2008 9:48 am |
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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.
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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
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PostPosted: Mon May 19, 2008 10:23 am |
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Joined: Thu Oct 31, 2002 5:39 pm
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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...
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PostPosted: Mon May 19, 2008 10:32 am |
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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....
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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?
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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
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PostPosted: Tue May 20, 2008 1:03 am |
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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.
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Joined: Mon Jan 15, 2007 5:05 pm
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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.
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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
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PostPosted: Tue May 20, 2008 9:47 am |
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Joined: Thu Oct 31, 2002 5:39 pm
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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.
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Holley Idle Transfer Slot
PostPosted: Tue May 20, 2008 12:17 pm |
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Joined: Mon Jan 15, 2007 5:05 pm
Posts: 3767
Location: Black Diamond, WA
Car Model: | Dan, 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. Do you have any books with specs on what this adjustment should be
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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
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PostPosted: Tue May 20, 2008 2:38 pm |
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| Offline | | Board Sponsor & Contributor |
Joined: Thu Oct 31, 2002 5:39 pm
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Car Model: | Do you have any books with specs on what this adjustment should be It's not a question of specs. This screw was adjusted 'live' (dynamically) on a flow bench at the end of the carburetor assembly line. It was not intended for field adjustment once the carb was built and out the door.
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Holley Idle Transfer Slot Modifications
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