I found this photo showing the port to plug on a 4 corner idle system.

 

I have had great results on Quick Fuel with 4 corner idle carburetors by eliminating this constant secondary idle ports. After all, that is what the rear adjustment screws are for.

But what would a 2 corner Holley or Quick Fuel act like with this same secondary constant idle feed plugged as shown in my #2 post photo? I understand there is only a transition slot feeding with no .022” to .027” commonly drilled constant port In a 2 corner system. Just has the impression to me of a fixed rate fuel feed that is not adjustable.

 

I know this is an old thread but I have to ask. What did you do to plug these ports? I also heard that I should plug the kill bleeds as well. I assume the same process to plug them is using 6-32 or 8-32 set screws like IFR’s? I have a Q-750 with these constant feed ports and I’m relocating my IFR’s to the lower position, blocking two of the emulsion ports. Not sure the size of the ports yet but if they’re bigger than .028 then I’ll use set screws to make them that size. I currently have 74/84 jets but I’ll be leaning that out. 33 IAB and 73 HSAB. Not sure the PVCR size yet. Just trying to get the carb sorted out. If you have any advice on anything I need to change then please let me know, thanks.

 

Do not plug your idle discharge ports on the front or rear of your Quick fuel carb. Those feed the idle circuit and the mixture screw adjustments you make on the carb are the air and fuel mixture on the idle circuit that feeds the engine when in gear and slightly off idle before the transfer slot takes over. On a two corner idle carb setup you would not want to plug up the secondary idle discharge port feed hole below the transfer slot as they are there for a reason. One to help the idle and feed the back cylinders of the engine and also to help keep fresh fuel on the secondary side of things.

On your four corner idle carb the base plate that Holley uses on them on most of there street carbs they have the secondary idle constant feed port below the transfer slot in order to use those base plates on either a two corner idle setup or a four corner idle setup. If using that base plate on a four corner idle setup and the rear has the normal idle discharge port in the rear then the tiny discharge port below the transfer slot can be plugged and it won't hurt anything. Now if your running it on a two corner idle carb then it has to be there as the outer discharge ports will not be in effect and functional and this the ports below the transfer slots are needed.

The difference is on the Holley two corner idle older style non 4 corner idle style base plates they don't have the rear normal location idle discharge ports on them and if ever converting one to a four corner idle you have to add them and then plug the tiny ones if you wish. I honestly just leave mine alone and have not had any problems with the idle being too over rich and other problems after its been tuned well. Also do not plug your kill bleeds on the metering blocks they are there for a reason.

I can't get into the whole science of them like other might be able to explain but with down leg boosters they are a more critical thing vs a straight leg booster setup. Also on emulsion ports you have to be careful on what you plug as some are above fuel level and some below. If its a 5 port emulsion block on each side then normally you would plug the number 2 and 4 spot and leave the rest open. Keep them all around .028 for a good starting point.

If its a 4 emulsion port block then normally you block holes 2 and 4 or if just number 4 and have that as either a two hole emulsion or three hole emulsion setup. If your blocks are the three port ones then I would not recommend plugging any of them as if you were to plug one of the holes your going to have unexpected issues on things as they are spaced different vs the other metering blocks and the area and level of the emulsion ports in relation to fuel bowl fuel level is more critical then one may think. Outside of having an o2 wide band air fuel ratio gauge to track things it not something just so easy to mess with and you can end doing a lot of hours chasing your tail.

I have never messed with those super sensitive areas of tuning and only stick with jetting and idle feed restrictors and minor tweaks to air bleeds and the power valve channel restrictors and the normal basic tuning and adjustments of carbs. Just because you read about many things folks have done to those emulsion areas and it worked for them and you automatically think you have to go out and do it as well is where one can get into a lot of trouble if you don't know what your getting into.

If my metering blocks are 4 hole emulsion then I plug the numbers 2 and 4 spots and have it as a two hole emulsion and leave it at .028 size. On a three emulsion port metering block I just leave it alone as when using a two or three port emulsion setup on any of the Quick fuel carbs or Holley I have not have had any difference in overall performance with that setup.

Same thing with putting the idle feed restrictors from up top to the bottom position of the metering block. I have ran it both ways and in almost everything I have had built over the years it has not played much of any night and day difference in tune or function and how the carb did on said build. It is at times needed on certain builds but not all. Same thing with putting restrictors in the main body for the transfer slot being a bit bigger on the Quick fuel base plates vs the older Holley styles with the slightly smaller transfer slots.

Some builds can use them and some not. I have always been able to tune mine and not have to do that mod. But like everything results will vary. Below are some photos that might help on the blocks.

 

Do not plug your idle discharge ports on the front or rear of your Quick fuel carb. Those feed the idle circuit and the mixture screw adjustments you make on the carb are the air and fuel mixture on the idle circuit that feeds the engine when in gear and slightly off idle before the transfer slot takes over. On a two corner idle carb setup you would not want to plug up the secondary idle discharge port feed hole below the transfer slot as they are there for a reason. One to help the idle and feed the back cylinders of the engine and also to help keep fresh fuel on the secondary side of things.

On your four corner idle carb the base plate that Holley uses on them on most of there street carbs they have the secondary idle constant feed port below the transfer slot in order to use those base plates on either a two corner idle setup or a four corner idle setup. If using that base plate on a four corner idle setup and the rear has the normal idle discharge port in the rear then the tiny discharge port below the transfer slot can be plugged and it won't hurt anything. Now if your running it on a two corner idle carb then it has to be there as the outer discharge ports will not be in effect and functional and this the ports below the transfer slots are needed.

The difference is on the Holley two corner idle older style non 4 corner idle style base plates they don't have the rear normal location idle discharge ports on them and if ever converting one to a four corner idle you have to add them and then plug the tiny ones if you wish. I honestly just leave mine alone and have not had any problems with the idle being too over rich and other problems after its been tuned well. Also do not plug your kill bleeds on the metering blocks they are there for a reason.

I can't get into the whole science of them like other might be able to explain but with down leg boosters they are a more critical thing vs a straight leg booster setup. Also on emulsion ports you have to be careful on what you plug as some are above fuel level and some below. If its a 5 port emulsion block on each side then normally you would plug the number 2 and 4 spot and leave the rest open. Keep them all around .028 for a good starting point.

If its a 4 emulsion port block then normally you block holes 2 and 4 or if just number 4 and have that as either a two hole emulsion or three hole emulsion setup. If your blocks are the three port ones then I would not recommend plugging any of them as if you were to plug one of the holes your going to have unexpected issues on things as they are spaced different vs the other metering blocks and the area and level of the emulsion ports in relation to fuel bowl fuel level is more critical then one may think. Outside of having an o2 wide band air fuel ratio gauge to track things it not something just so easy to mess with and you can end doing a lot of hours chasing your tail.

I have never messed with those super sensitive areas of tuning and only stick with jetting and idle feed restrictors and minor tweaks to air bleeds and the power valve channel restrictors and the normal basic tuning and adjustments of carbs. Just because you read about many things folks have done to those emulsion areas and it worked for them and you automatically think you have to go out and do it as well is where one can get into a lot of trouble if you don't know what your getting into.

If my metering blocks are 4 hole emulsion then I plug the numbers 2 and 4 spots and have it as a two hole emulsion and leave it at .028 size. On a three emulsion port metering block I just leave it alone as when using a two or three port emulsion setup on any of the Quick fuel carbs or Holley I have not have had any difference in overall performance with that setup.

Same thing with putting the idle feed restrictors from up top to the bottom position of the metering block. I have ran it both ways and in almost everything I have had built over the years it has not played much of any night and day difference in tune or function and how the carb did on said build. It is at times needed on certain builds but not all. Same thing with putting restrictors in the main body for the transfer slot being a bit bigger on the Quick fuel base plates vs the older Holley styles with the slightly smaller transfer slots.

Some builds can use them and some not. I have always been able to tune mine and not have to do that mod. But like everything results will vary. Below are some photos that might help on the blocks. View attachment 630583

Thanks for the information. I finally got time to work on the carb. Did some changes one at a time and the engine is loving it. My most recent change was decreasing the IFR’s to .028 and keeping the stock 73 IAB’s. My mixture screws are out 1.5 turns just to make it idle. I didn’t want to increase the idle because I set the transfer slots and at 1.5 turns it would idle and I was able to lower the idle but it wouldn’t idle with them at 1 turn. I think I may have too much transfer slot exposed on the rear. I was always taught to set them up equal but after reading I see that it may be best to just adjust the idle with the secondary idle speed without exposing the transfer slot. I’m wondering if I should drop the IAB’s to 70’s perhaps or increase the IFR to .031’s again.

 

Here is my corvette 3810 with dribble hole.

These I plugged with epoxy. The IFR needed to be changed as well as IFR.
Listing below covers all modifications
Holley 3810 on White ‘67 Corvette 327/350 HP date 7/13/21. Remains as 2 corner idle
Epoxy sealed constant feed holes both primary & secondary holes were about .022”
(Weird having them in primaries)
Primary jet .065” changed to .066”
Secondary jet .068” (stamped #65) Secondary meter plate changed to meter block
Power valve 6.5 changed to 5.5
PVR .040 same as original
IAB .070” primary changed to .062”
IAB .031” secondary changed to .037”
MAB .031” primary
MAB .0225” secondary changed secondary MAB .031”
Idle Fuel Restrictions (IFR) .029” primary & .029” secondary in lower positions
Emulsion jets on both meter blocks all are .028” 2 per side same as original
Anti-Siphon air bleeds are .028” front & rear
IFR primary was .031” & rear was #22 meter plate w/.076” & .028” IFR
(Original meter plate p/n 34R9716-22 equals #65 main jet per Holley chart)
Accelerator pump squirter .025” w/no tubes changed to .025” w/brass tubes
Squirter cam red #240 but worn position #1 changed to white #218 position #1

I had to make similar changes on my 57 Nomad BBC 427
Quick Fuel HR580VS 4 corner idle
IFR-.028” upper position primary & secondary chg to .025” lower position
PVR-.043” changed to .0395”
Idle air bleed .070/.073. changed to .0725”
High speed air bleed .031”
Primary Jet Size: #66. (.066”)
Primary Power Valve (Hg): 6.5 Hg
Transition slot restriction added .0815” both front & rear, was .106” hole
Secondary Jet Size: #70 (.073”) changed to .067”
Emulsions .029”, .031”, .032” changed all to .025”
Squirter nozzle .028” changed to .025”
Squirter Cam was pink position #1 changed to red #240 position #1
Epoxy plugged the .027” secondary continuous idle ports
Down leg booster spec — no they are straight leg
Carburetor Height 3.250 in. 1 9/16 in. throttle bore. 7/8-20 in.fuel inlets.

I know not all changes are conventional and fall within the general published settings. But these work for my cars. Most of HOLLEY type carbs produced today are WAY TOO RICH IN EVERY ORIFACE for street engine use. I’m not drag racing my cars and expect them to perform on the street and be comfortable to drive.

 

LSGbody if you have your secondary transfer slot showing the same as the front then you might have it just showing too much and it most likely is more opened then the front as the secondary transfer slots on most Quick fuel carbs with either the cast or billet plates, the secondary transfer slot sits up about .020 higher in the rear vs the front and trying to equal them out ends up making the rear a lot higher then needed and makes things more out of balance.

The thing with the secondary is you want it to just allow enough air through in order to have your primary idle set where you want it without having the primary transfer slot over exposed and also have adjustment with your mixture screws and your primary idle setting to not be too fat. Sometimes having the secondary side open up too much vs in relation to the primary side can cause off idle and cruising issues at low speeds but not always.

What is the specs of your engine anyways while I am at it just out of curiosity. Since you went down on the idle feed restrictors and your out at 1.5 turns on the screws and anything less then 1 turn makes it quit and if your secondary side is open up that much to have the rear transfer slot showing at around .020 which would equal a lot of opening and would be similar to like having the primary side open up too much.

If you close them up some and then come to a point that in order for your carb to idle and you had to open up the primary side more then where its past square or about no more then .020 to .030 max, then I would say the .028 ifr size might be too lean and you would have to try .031 and readjust things and see where it goes too.

On the four corner idle carbs when its properly tuned for the best idle calibration and this is not etched in stone but a good indicator and is in my experience and also a lot of other tuners over the years have came up with a range to where the all four idle mixture screws are around 3/4 to no more then 1 full turn out on all four corners being equally set and the primary transfer slot showing no more then .020 to .030 and square and the secondary side open up only just enough to keep the primary side where it needs to be and the idle mixture screws adjust like they should.

On some engines with bigger cams and a lot of overlap that require a lot richer mixture, the mixture screws on all four corners can be just as little as only 1/2 to no more then 3/4 of a turn out to get the proper idle setting in relation to the proper primary and secondary butterfly setting. I honestly think your really close from what you described and just need a few minor tweaks. I would readjust your secondary side and see if you can close them up just a hair like maybe a 1/4 to half a turn.

I would not want to close it too much more then that then you will be off on the front side. I would see how it does and readjust your mixture screws and if you have to have a lot more then 1 turn out for it to idle then at least try it and see how it performs off idle etc. If it ends up running and doing fine with where its set at on the secondary side after making your other changes then that is fine too. Its just a balance game between the three areas of the idle circuit setting of the primary and secondary butterflies and the mixture screws.

Leave the idle air bleeds alone for now. They don't have much as an impact on turning like changing out the idle feed restrictors does. They have to be change around .004 size difference at a time just to get a change. I normally if I go to mess with them I always get my ifr size sorted out first and then try different idle air bleed size to fine tweak the final setting of the idle circuit. Good luck and glad to hear your making progress.

 

LSGbody if you have your secondary transfer slot showing the same as the front then you might have it just showing too much and it most likely is more opened then the front as the secondary transfer slots on most Quick fuel carbs with either the cast or billet plates, the secondary transfer slot sits up about .020 higher in the rear vs the front and trying to equal them out ends up making the rear a lot higher then needed and makes things more out of balance.

The thing with the secondary is you want it to just allow enough air through in order to have your primary idle set where you want it without having the primary transfer slot over exposed and also have adjustment with your mixture screws and your primary idle setting to not be too fat. Sometimes having the secondary side open up too much vs in relation to the primary side can cause off idle and cruising issues at low speeds but not always.

What is the specs of your engine anyways while I am at it just out of curiosity. Since you went down on the idle feed restrictors and your out at 1.5 turns on the screws and anything less then 1 turn makes it quit and if your secondary side is open up that much to have the rear transfer slot showing at around .020 which would equal a lot of opening and would be similar to like having the primary side open up too much.

If you close them up some and then come to a point that in order for your carb to idle and you had to open up the primary side more then where its past square or about no more then .020 to .030 max, then I would say the .028 ifr size might be too lean and you would have to try .031 and readjust things and see where it goes too.

On the four corner idle carbs when its properly tuned for the best idle calibration and this is not etched in stone but a good indicator and is in my experience and also a lot of other tuners over the years have came up with a range to where the all four idle mixture screws are around 3/4 to no more then 1 full turn out on all four corners being equally set and the primary transfer slot showing no more then .020 to .030 and square and the secondary side open up only just enough to keep the primary side where it needs to be and the idle mixture screws adjust like they should.

On some engines with bigger cams and a lot of overlap that require a lot richer mixture, the mixture screws on all four corners can be just as little as only 1/2 to no more then 3/4 of a turn out to get the proper idle setting in relation to the proper primary and secondary butterfly setting. I honestly think your really close from what you described and just need a few minor tweaks. I would readjust your secondary side and see if you can close them up just a hair like maybe a 1/4 to half a turn.

I would not want to close it too much more then that then you will be off on the front side. I would see how it does and readjust your mixture screws and if you have to have a lot more then 1 turn out for it to idle then at least try it and see how it performs off idle etc. If it ends up running and doing fine with where its set at on the secondary side after making your other changes then that is fine too. Its just a balance game between the three areas of the idle circuit setting of the primary and secondary butterflies and the mixture screws.

Leave the idle air bleeds alone for now. They don't have much as an impact on turning like changing out the idle feed restrictors does. They have to be change around .004 size difference at a time just to get a change. I normally if I go to mess with them I always get my ifr size sorted out first and then try different idle air bleed size to fine tweak the final setting of the idle circuit. Good luck and glad to hear your making progress.

It’ll idle with screws at 1 turn out with the .031’s. Carb cane stock with .033’s. 400 SBC 9.92:1 it produces 10” vacuum at idle. The cam specs are below but I have 1.6 rockers. Cam installed straight up.

Advertised Intake Duration: 292
Advertised Exhaust Duration: 292
Intake Duration at .050 Inch Lift: 244
Exhaust Duration at .050 Inch Lift: 244
Intake Valve Lift: 0.501
Exhaust Valve Lift: 0.501
Lobe Lift Intake: 0.334
Lobe Lift Exhaust: 0.334
Lobe Separation: 110
Intake Centerline: 106
Exhaust Close ATDC: 34
Intake Open BTDC: 37
Exhaust Open BBDC: 77
Intake Close ABDC: 74

 

That sounds like the old comp cam magnum 292h flat tappet cam specs. I had that as my very first performance cam and loved the sound of it. With your specs I would bet by guessing and with experience that your idle circuit ifr size might end up wanting to be more around the .031 size front and rear vs the .028 size. Just depends on build to build though with all the different factors such as cam specs and compression and cylinder head flow and timing etc.

Most of the time with bigger cams and low vacuum I have usually needed at least a .031 ifr size minimum to get a correctly calibrate idle to have it rich enough to idle correctly but yet not be too rich to cause poor fuel mileage for said build and foul out plugs etc. Those bigger cams like a lot of timing and a richer mixture and higher idle setting vs milder builds. I bet that engine runs pretty well if it has a good set of heads on it.

 

After driving it it seems a little too lean. If I barely touch the gas then it seems like it’s killing the engine. Will primary jets have any affect when you give it gas at idle? It will idle fine but when I give it gas it feels sluggish now and if I barely open the throttle it feels as though it’s sucking in to much air and not enough fuel and the idle will drop. Opening the idle mixture screws only makes the idle worse so I think the idle is where it’s supposed to be. Accelerator pump and cam are set up correctly. I have 31 squirters currently. It’s not backfiring through the carb or anything. I can drop back down to .031 IFR’s now that I’ve determined the .033’s did not fix this issue. I can’t tell if it’s too much air or fuel from the squirters that’s making it feel sluggish. If it’s not backfiring through the carb and since I’ve already tried increasing the IFR size and it didn’t make a difference with the off idle transition does that mean I may need a bigger squirter size perhaps?

 

That is what I was wondering after seeing your specs. The .028 ifr size front back works on small blocks with milder cams around the 220@50 range on average depending on a few factors. Yours at minimum would be a .031 size front and rear keeping things square or the .033 at the most on average. Like I put it your idle mixture screws depending on a few things should idle at around 3/4 to 1 turn when in gear on all four mixture screws and if all things else being correct such as your ifr size and butterfly adjustments it should run really strong and well with proper timing and other things being in good order on average range on a four corner Holley style carb in my experience on a good baseline setting.

 

Yeah, the carb doesn’t bog if I quickly open the throttle but it just seems slow to pick RPM up. IFR size and idle mixture screw adjustment don’t make it go away. I know the engine so I can tell that it’s low on power.

 

Camshaft is too big not necessary for street car. You want to be less than 225 degrees or you are asking for a sloppy compromise in operation at best. Your c/r is too low for this cam. Drag racing parts are for drag racing. Another thing the cam ramp rates are too fast and longevity is questionable at best. No sugar coating just truth.

 

Cam has been in the engine for over 7 years. Just wanted to lean the carb out some. It ran good with it rich but the plugs were letting me know it’s rich. The transfer slot hole in the main body was .1285 and the restrictors I installed was .081 but clearly it’s too lean even with .033 IFR’s. It idled best with .031’s. I have to get bigger set screws (10-32) because the 8-32’s are maxed out.

 

Test your thought by putting say .066 IAB. That will richer idle since your vacuum is low and may not be pulling. Easy test. Keep in mind big sloppy idle cams are not what the vacuum signal needs to be. IMHO going from .028 to .031 or .033 IFR is a lot of fuel change. Transfer slot restricted to .081 is about right. Generally modern carbs right out of the box are way big in this area too.

 

Tried that and it doesn’t seem to help. Maybe it’s a rich bog and not a lean bog. Kind of difficult to tell the difference. If I stab the throttle it won’t hesitate but if I open the gently open the throttle a few times back to back it will cause the engine to sound like it wants to die like it’s getting smothered and bog down. I’ll try to go the other way and just use smaller t slot restrictors perhaps since it’s off the car. Maybe I’ll put in .078’s perhaps? When the carb was completely stock like quick fuel sent it to me it ran good but was super rich everywhere. Changing the IFR’s didn’t affect the off idle but the idle mixture screws are responsive and didn’t need to be opened up as far when I increased their size so that was a good sign. The original transfer slot hole was around .1285. It was a couple of shavings in the hole after tapping it but I blew them out with compressed air. I can’t see anymore in the hole and I even removed the baseplate to see if anymore were in the slot but it was clean. I seriously doubt it’s clogged or anything.

 

Older Holley’s had small passages for transfer slot around .078” to .081” range. But the T slots were much smaller width and length. I have no issue with idle screws 1 and half turns out. In old days that was normal. What do the plugs say? Rich or lean? Exhaust smell? Second thought the big cam will make these observations worthless for idle settings. Smaller IFR’s will generally help transition when hitting throttle with lower vacuum. But big cam and lower C/R hurts response. Are you sure you have enough timing advance? More advance with big cam also should help.

 

Older Holley’s had small passages for transfer slot around .078” to .081” range. But the T slots were much smaller width and length. I have no issue with idle screws 1 and half turns out. In old days that was normal. What do the plugs say? Rich or lean? Exhaust smell? Second thought the big cam will make these observations worthless for idle settings. Smaller IFR’s will generally help transition when hitting throttle with lower vacuum. But big cam and lower C/R hurts response. Are you sure you have enough timing advance? More advance with big cam also should help.

 

Older Holley’s had small passages for transfer slot around .078” to .081” range. But the T slots were much smaller width and length. I have no issue with idle screws 1 and half turns out. In old days that was normal. What do the plugs say? Rich or lean? Exhaust smell? Second thought the big cam will make these observations worthless for idle settings. Smaller IFR’s will generally help transition when hitting throttle with lower vacuum. But big cam and lower C/R hurts response. Are you sure you have enough timing advance? More advance with big cam also should help.

 

Older Holley’s had small passages for transfer slot around .078” to .081” range. But the T slots were much smaller width and length. I have no issue with idle screws 1 and half turns out. In old days that was normal. What do the plugs say? Rich or lean? Exhaust smell? Second thought the big cam will make these observations worthless for idle settings. Smaller IFR’s will generally help transition when hitting throttle with lower vacuum. But big cam and lower C/R hurts response. Are you sure you have enough timing advance? More advance with big cam also should help.

 

Plenty of timing. I’ve even tried increasing initial to see if it helps.