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Discussion Starter · #1 ·
I have a new AFR gauge, and I am ready to start tuning on the carb. My first short run on the road showed numbers all pig rich. 10.5 to 12 at best. Idles at a steady 11. So there is plenty of room for improvement.
I would like to use this as my notebook. Last night I recorded the starting specs for the carb in the notebook I have been keeping with all the specs and part numbers for the recent rebuild of this 355 SBC, kinda like my diary for the engine with any changes I make. About 50 pages worth. Pretty detailed. This morning I came out to find my 7 month old shop puppy, Barney, a loveable? Black Lab, had gotten it off the bench and destroyed it. :mad:Nothing salvageable. I forgot to put it away last night. He'll have to eat the computer to get this one. So follow along if you would like or not. This is liable to be a long drawn out process.
Here is what I am working with:
Car:
1926 Ford Model T
700r4 trans
3.80:1 gear 8" Ford rear end
28" rear tire
2500#
Engine:
I started with a Goodwrench 350. I only used the block, crank, pan and the QFT SL-600-VS carb that I am working on now. Block bored and decked. Crank polished and balanced. Scat rods. Flat top KB's. CR is 9.96:1.
ProMaxx Maxx series aluminum heads 183cc intake volume, 64cc CC, 2.02/1.60
Edelbrock Performer RPM manifold
Lake style headers
Pertronix Flamethrower Ignitor III distributor,,,, 16 initial + 18 mechanical all in about 2700 with 16 vacuum adv on full manifold vacuum (I may limit the vac advance a little bit)
15-16 InHg at 750 rpm
Carb:
QFT SL-600-VS Out of the box the idle mix screws had no effect on the idle. So with the help of eric32, I leaned up the idle circuit and converted the carb to 4 corner idle with a QFT 34-9 metering block. Changed the primary IFR's to .028 from the stock .031 and changed the secondary idle air bleeds to .070 from the stock .039. That put the control back in the idle mix screws. It has been running great for 5000 miles on the engine before rebuild. Now on the new rebuild it has developed an off idle bog with the occasional backfire on initial hit of the throttle. So I put (4) .033 IFR's in it and changed the squirter to .035 from the stock .031. Now it runs pretty good. But I am sure the MPG's have gone to hell. And performance could be better. This is where the AFR gauge came into the picture. Idling in the shop last night the idle AFR was 11:1. Cruise down the road was about 12:1, [email protected] WOT was below 11:1. So I know the whole thing is fat. I went back to the .028 IFR"S and left the .035 squirter in it, but haven't tested yet. I think next test may be to see what changing main jets does for it.
It snowed last night and is about 31 degrees now and will be 70 tomorrow, so I am going to hold off any judgement until a test drive tomorrow.
1926 T NEW Wheels.JPG

I know a lot of you guys have seen my ride, but here it is again anyway.
To be continued.
 

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Main jets won't do anything for you until you are drawing fuel from the boosters. Certainly that's not happening when youre putzing about at 1800 rpm. You're running off the IFRs at that point.

What camshaft? Sounds pretty mild.

Get the IFRs where you want the mix to be during your 1800 rpm steady cruise, but first make sure the transfer slot in primary side is appropriately covered/uncovered. If you have no mix adjustment with mix screws then there is something really wrong. It is my understanding that the IFRs and IABs should all be the same on a normal carb. Doesn't sound like what you have. Once you have this right and no stumble, you can start concerning yourself with main jets and finally PVR/secondary jets at higher RPM. Timing sounds good.
 

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Discussion Starter · #3 ·
Mix screws having no effect was taken care of when I went to the 4 corner idle screws with the 34-9 secondary metering block. The mix screws do affect the idle and are out 5/8 turn. There is no stumble now. Just very rich afr's. I am aware that the main jets will not affect the idle afr. But above 2000 rpm cruise is very rich also. I know. One change at a time. But I sometimes cheat on that . Working both ends to the middle. :). Trans slot is within the .020 -.040, which on this carb is between 1/4 and 1/2 turn in from contact. Currently at about .030. I had to lower the 2ndary idle screw about 1/4 turn in from 1/2 in to get the idle low enough also. The way I see it is:
Idle through 1800-2000 = IFR's
Cruise under 1800-2000 = IFR's
Cruise over 1800-2000 = Main Jets
Acceleration = Discharge Nozzle (squirter, shooter) with vacuum above my 6.5 power valve
WOT= Main Jets + Power Valve + PV Cannel Restrictors + vacuum secondary setting
Please correct me if I am wrong. Wouldn't be the first time.
Cam is from Straub. 215/224 @ .050, 284/296 adv dur, .470/.490 @1.5, 112LSA
I'm just waiting on the weather. No point in tuning for 30 degrees, when 70's are coming in a few days.
 

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You say vacuum above poet valve , the power valve is held closed by vacuum , when the vacuum drops below the (6.5) the valve opens & remains open until the vacuum is above the setting . I'd guess you're running on the transition circuit up until 2500 + .
 

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Discussion Starter · #5 ·
From what I read, the transition circuit is controlled by the IFR. I think the idle port and the trans slot are both fed through the IFR with the split ratio between the two being controlled by the position of the throttle plate (how much trans slot is showing) and the idle port being controlled by the idle mix screw. The power valve basically becomes another main jet at WOT. I think I have that right?
I bought David Vizard's "How to Super Tune and Modify Holley Carburetors" . I have had it for years, but never could get into it. I think because I didn't have a specific goal in mind. In the last few days I have been devouring it. I got a long ways to go. Anyway, Vizard says that the main jets don't come in until about 3000 rpms. I think I can find the rpms where the main jets become active by playing with the jets and watching the AFR.
I think the main jet circuit will be the most difficult to tune. By the time you are on the main jet you are going pretty fast. Third gear in the 700r4 (1:1) helps with that. I don't need any high speed driving awards while tuning the carb :).
 

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There is one thing I have read about and I don't know for sure if this would be the case with your carb or not and I myself have not had this problem but its something that can be looked into but extreme caution must be made before attempting this procedure. On the quick fuel carbs and there base plates, compared to an original factory Holley like say for instance a Holley 1850 600 cfm carburetor which is what I am building for my 377 build and then swap it over to my 350 once its done, the base plates on the quick fuel carbs have a slightly longer and wider transfer slot on the front and back compared to the holley base plates regardless of a 4 corner or 2 corner idle and with the quick fuel transfer slot being slightly longer and wider it can make for a situation on certain builds for a pig rich mixture on the idle circuit and you not being able to lean it out enough within a proper range of adjustment by changing the idle feed restrictors or the idle air bleeds.

For the most part the idle air bleeds rarely need to be changed until ultra fine tune but your .070 should be adequate enough to keep as is and even on mine I have kept mine within .070 to .078 at the most and been fine. On the procedure what I am talking about is where on the main body on the transfer slot feed holes on the primary side of the main body folks will drill the main body and tap them for either a 8-32x1/8 brass allen set screw or a 10-32x1/8 brass allen set screw and drill them to a certain size to act as a transfer slot restrictor and function just like an idle fee restrictor in the metering block. I have read where folks had a pig rich transfer slot circuit and when they tried to lean it out with the Idle feed restrictors going smaller they was unable to go small enough to get a certain air fuel ratio to be lean enough to where it would run right and then when they had to enrichen it up just a hair it would end up to rich and they did not have much of a range to get the transfer slot calibrated good enough to what they wanted.

So in that effect they would drill and tap the main body for the brass allen set screws and then drill them to a certain size ranging from anywhere from .040 to .070 on average and use that on the primary side to help restrict the transfer slot circuit even more and sometimes it would allow them more range to fine tune the transfer slot circuit on there carbs but that is only in certain situations and I don't know for sure that would be your case. Like I have mentioned before your cam for its size has a good amount of overlap and I think it was around 60 degrees from seat to seat and a camshaft with more overlap will always require a more rich mixture vs a cam like mine which only has 42 degrees give or take a few of overlap seat to seat, can run leaner vs a similar sized cam with a lot more overlap.

I personally don't know if that would help you out or not but its something that can be d-one but once you have drilled out the main body transfer hole that feeds the base plate you would have to make sure you have enough set screws on hand and I don't know if you can put it back to exactly stock specs for the diameter hole size as I have not measured what the exact size is but you would have to use a 10-32 brass allen set screw size to be on the safe side as the 8-32 size can only be drilled to about .074 at the biggest before you would start to hit the hex walls that you use to screw them in with an allen wrench.

The 10-32 will allow you to go beyond .074 with no issues before you would start to hit the walls of the set screw for the allen wrench. I have noticed a slight difference when tuning the idle circuit by using a holley base plate vs a quick fuel base plate but I have never encountered that much of a problem to have to ever do that modification and I don't use a air fuel ratio gauge and just go by what my engine wants and I can say my 377 has taken quite a bit more of a richer mixture vs my old 350. I have kept my old notes as well from my previous builds and I can say your setup is very close to some of my previous builds and they are pretty close to what your carb is setup at but that was with camshafts with a lot more overlap vs the current one I have.

My previous 350 build that had a camshaft of 282/290 231/[email protected] 50 535/550 lift and 110 LSA and 66 degrees of overlap seat to seat and it was a lunati voodoo hydraulic roller cam and I ran a good amount of timing with it and I with a four corner idle carb had to run the .033 idle feed restrictor size front and back and nothing less would allow it to idle right or run right and would cause a lot of drivability issues and my mixture screws to have to be way out in order to idle and would quit when dropping into gear and need to much opening of the butterflies.

When I took my double pumper off of that build and put on a 2 corner idle Proform 650 vacuum secondary which is basically a quick fuel carburetor with the name Proform stamped on it but the same situation I kept the carb on the stock settings out of the box and could for the life of me get it to idle good and it was just to lean and had to have my idle mixture screws out so far it was unreal at two plus more turns.

Going by my Holley tuning book on carbs and also by researching other peoples builds and comparing things from one carb style calibration to another and also by experience I can tell more easy on what my engine wants and can be close with just a little bit of adjustment and minor changes here and there to get what I need.

I started out with a .033 primary ifr size and .039 secondary side which was a metering plate that takes jets and had changeable brass allen set screws for the idle feed restrictor size. I had to go up a few changes at a time and ended up at .037 primary idle feed restrictor and kept the secondary at .039 and the air bleeds were .070 primary and .039 secondary since it was a two corner idle. Now that seemed to be a real rich mixture but it allowed me to have a lot more range of idle mixture screw adjustment and also to keep my transfer slot exposure correct and also my idle mixture screws were about 1 and 3/4 of a turn out.

On a two corner idle carb if you are within a range of 1 turn out at the least and no more at two turns out and have a decent amount of adjustability on the mixture screws and it is setup correctly on the throttle opening and the correct amount of timing then its pretty close as to what it is wanting without being to rich but at least lean enough to not case any driving issues.

On a four corner idle setup the same principal applies and if you can get no less then half a turn on all four but go up to at least an 1/8 of a turn past 3/4 on all four then its within range of what the engine wants but that is not etched in stone but that is what has worked for me to have it as lean as possible but not be to lean and also not to rich to foul out my plugs and chug down fuel and have driving issues and be to much or to little and be within a good range all around to run well.


On that 350 build I got 19 mpg and around 10 mpg driving in town and even though on paper it looks like it was pig rich and maybe if I did have an AFR gauge hooked up to it I might have shown a pig rich mixture but its what my engine liked and my plugs were clean and never any fuel fouled plug problems and the carb would adjust quite well on the mixture screws and run strong all across the board.

The thing also with using AFR gauges is you can't always get the leanest number as possible but is to use as a ultra fine tuning part to get the best tune possible for your carburetor but you can't always have the magic 14:5 to 1 ratio in every build, especially performance ones. From research with bigger cams or at least ones with a lot of overlap they always required a richer mixture and also you can't always get an accurate reading at all times in all situations from the AFR gauge as with the overlap being a lot more it causes exhaust gas reversion up through the intake manifold and thus affecting carb signal and also the mixture as well. And cause of that it always requires a richer mixture vs a cam with less overlap.

Your cam has a lot more seat to seat duration vs my cam of 268/272 220/[email protected] 510/510 lift with a 114 LSA 42 degrees of overlap seat to seat in my 377 build.

Your cam you have has a easier ramp rate compared to mine which has a faster ramp rate and less duration from seat to seat thus less overlap vs yours even though mine in my 377 is only slightly different then yours @ 50 duration specs. Maybe someone else can chime in more in having experience by using the AFR gauge for setting up on the carb.
 

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Also the thing with a 4 corner idle vs a 2 corner idle setup is the 4 corner idle setup is way more sensitive to adjustment vs a 2 corner idle on adjusting the mixture screws. On a 2 corner idle it takes just an 1/8 of a turn to make a difference if its setup correctly vs on a 2 corner idle setup it normally takes about a 1/4 of a turn on each screw to make a different in adjustment. That is why normally the 4 corner idle setup has less turns out on the mixture screws vs a 2 corner idle.

The 4 corner idle setup is like having two 2 barrels sitting back to back and each one is blocked off from the other and thus you have two ranges of adjustment vs just one. On the two corner idle setups you have only two mixture screws needing adjusting and feeding 8 cylinders vs the 4 corner idle setup which offers you two mixture screws for the front 4 cylinders and 4 for the back 4 cylinders and thus why they allow more fine tuning but is mostly used best for cams with a lot more duration seat to seat and with a hefty amount of overlap vs a two corner idle setup.
 

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I have found that sometimes when changing things on the engine like intake and camshaft, the carb requires a very different calibration. It seems like you have changed your engine significantly since you originally set up this carb. I think there is value in putting a carb back to factory original and starting from scratch again.
 

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His carb was a two corner idle setup and all he did was change it from a 2 corner idle to a 4 corner idle and put in a secondary metering block with idle mixture screws and removed the secondary metering plate that comes with the quick fuel 600 slayer. And he changed the secondary idle air bleeds to match the primary side. He started out with .028 idle feed restrictors on the metering blocks front and back and the idle air bleeds .070 matched front and back and it was to lean from my understanding and he had a lot of hesitation and issues of what sounds like to lean of an idle circuit calibration according to his specs of his build. The stock setting was a primary idle feed restrictor of .either .031 or .033 in the primary metering block and the secondary metering plate from my last time I have checked it had a .039 ifr size and the secondary idle air bleed was .039 out of the box setup as a two corner idle.

He had idle problems starting off with the .028 ifr size and bucking issues and backfire in certain situations but which conditions I can't recall right off hand.

The quick fuel slayer 600 carb main bodies are already made for a four corner idle setup from the factory and also on the base plate as well as it does not share fuel with the front like a holley two corner idle base plate does. All quick fuel does is take away the secondary metering block with idle mixture screws and put on a secondary metering plate that takes jets and also puts on smaller secondary idle air bleeds to enrichen up the secondary side of the idle mixture circuit on the carb since you can't adjust it and with it being a 2 corner idle setup on there slayer vacuum secondary carbs.

That is all about he has done from what I know.
 

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Discussion Starter · #10 ·
I have found that sometimes when changing things on the engine like intake and camshaft, the carb requires a very different calibration. It seems like you have changed your engine significantly since you originally set up this carb. I think there is value in putting a carb back to factory original and starting from scratch again.
Yes the engine is a completely different animal now.
I agree about going back to completely stock. I just converted all my fuel lines to braided hose andAN fittings. I don't remember the dimensions right now but the 4160 600 with a metering plate takes the narrower fuel line. I have to have the rear metering block to make my wider 4150 fuel line to make it so I don't have to change all the fuel lines. Or I would go back to completely stock just for test purposes. I do think the 4 corner idle is a definite improvement though.
 

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Discussion Starter · #11 ·
There is one thing I have read about and I don't know for sure if this would be the case with your carb or not and I myself have not had this problem but its something that can be looked into but extreme caution must be made before attempting this procedure. On the quick fuel carbs and there base plates, compared to an original factory Holley like say for instance a Holley 1850 600 cfm carburetor which is what I am building for my 377 build and then swap it over to my 350 once its done, the base plates on the quick fuel carbs have a slightly longer and wider transfer slot on the front and back compared to the holley base plates regardless of a 4 corner or 2 corner idle and with the quick fuel transfer slot being slightly longer and wider it can make for a situation on certain builds for a pig rich mixture on the idle circuit and you not being able to lean it out enough within a proper range of adjustment by changing the idle feed restrictors or the idle air bleeds.

For the most part the idle air bleeds rarely need to be changed until ultra fine tune but your .070 should be adequate enough to keep as is and even on mine I have kept mine within .070 to .078 at the most and been fine. On the procedure what I am talking about is where on the main body on the transfer slot feed holes on the primary side of the main body folks will drill the main body and tap them for either a 8-32x1/8 brass allen set screw or a 10-32x1/8 brass allen set screw and drill them to a certain size to act as a transfer slot restrictor and function just like an idle fee restrictor in the metering block. I have read where folks had a pig rich transfer slot circuit and when they tried to lean it out with the Idle feed restrictors going smaller they was unable to go small enough to get a certain air fuel ratio to be lean enough to where it would run right and then when they had to enrichen it up just a hair it would end up to rich and they did not have much of a range to get the transfer slot calibrated good enough to what they wanted.

So in that effect they would drill and tap the main body for the brass allen set screws and then drill them to a certain size ranging from anywhere from .040 to .070 on average and use that on the primary side to help restrict the transfer slot circuit even more and sometimes it would allow them more range to fine tune the transfer slot circuit on there carbs but that is only in certain situations and I don't know for sure that would be your case. Like I have mentioned before your cam for its size has a good amount of overlap and I think it was around 60 degrees from seat to seat and a camshaft with more overlap will always require a more rich mixture vs a cam like mine which only has 42 degrees give or take a few of overlap seat to seat, can run leaner vs a similar sized cam with a lot more overlap.

I personally don't know if that would help you out or not but its something that can be d-one but once you have drilled out the main body transfer hole that feeds the base plate you would have to make sure you have enough set screws on hand and I don't know if you can put it back to exactly stock specs for the diameter hole size as I have not measured what the exact size is but you would have to use a 10-32 brass allen set screw size to be on the safe side as the 8-32 size can only be drilled to about .074 at the biggest before you would start to hit the hex walls that you use to screw them in with an allen wrench.

The 10-32 will allow you to go beyond .074 with no issues before you would start to hit the walls of the set screw for the allen wrench. I have noticed a slight difference when tuning the idle circuit by using a holley base plate vs a quick fuel base plate but I have never encountered that much of a problem to have to ever do that modification and I don't use a air fuel ratio gauge and just go by what my engine wants and I can say my 377 has taken quite a bit more of a richer mixture vs my old 350. I have kept my old notes as well from my previous builds and I can say your setup is very close to some of my previous builds and they are pretty close to what your carb is setup at but that was with camshafts with a lot more overlap vs the current one I have.

My previous 350 build that had a camshaft of 282/290 231/[email protected] 50 535/550 lift and 110 LSA and 66 degrees of overlap seat to seat and it was a lunati voodoo hydraulic roller cam and I ran a good amount of timing with it and I with a four corner idle carb had to run the .033 idle feed restrictor size front and back and nothing less would allow it to idle right or run right and would cause a lot of drivability issues and my mixture screws to have to be way out in order to idle and would quit when dropping into gear and need to much opening of the butterflies.

When I took my double pumper off of that build and put on a 2 corner idle Proform 650 vacuum secondary which is basically a quick fuel carburetor with the name Proform stamped on it but the same situation I kept the carb on the stock settings out of the box and could for the life of me get it to idle good and it was just to lean and had to have my idle mixture screws out so far it was unreal at two plus more turns.

Going by my Holley tuning book on carbs and also by researching other peoples builds and comparing things from one carb style calibration to another and also by experience I can tell more easy on what my engine wants and can be close with just a little bit of adjustment and minor changes here and there to get what I need.

I started out with a .033 primary ifr size and .039 secondary side which was a metering plate that takes jets and had changeable brass allen set screws for the idle feed restrictor size. I had to go up a few changes at a time and ended up at .037 primary idle feed restrictor and kept the secondary at .039 and the air bleeds were .070 primary and .039 secondary since it was a two corner idle. Now that seemed to be a real rich mixture but it allowed me to have a lot more range of idle mixture screw adjustment and also to keep my transfer slot exposure correct and also my idle mixture screws were about 1 and 3/4 of a turn out.

On a two corner idle carb if you are within a range of 1 turn out at the least and no more at two turns out and have a decent amount of adjustability on the mixture screws and it is setup correctly on the throttle opening and the correct amount of timing then its pretty close as to what it is wanting without being to rich but at least lean enough to not case any driving issues.

On a four corner idle setup the same principal applies and if you can get no less then half a turn on all four but go up to at least an 1/8 of a turn past 3/4 on all four then its within range of what the engine wants but that is not etched in stone but that is what has worked for me to have it as lean as possible but not be to lean and also not to rich to foul out my plugs and chug down fuel and have driving issues and be to much or to little and be within a good range all around to run well.


On that 350 build I got 19 mpg and around 10 mpg driving in town and even though on paper it looks like it was pig rich and maybe if I did have an AFR gauge hooked up to it I might have shown a pig rich mixture but its what my engine liked and my plugs were clean and never any fuel fouled plug problems and the carb would adjust quite well on the mixture screws and run strong all across the board.

The thing also with using AFR gauges is you can't always get the leanest number as possible but is to use as a ultra fine tuning part to get the best tune possible for your carburetor but you can't always have the magic 14:5 to 1 ratio in every build, especially performance ones. From research with bigger cams or at least ones with a lot of overlap they always required a richer mixture and also you can't always get an accurate reading at all times in all situations from the AFR gauge as with the overlap being a lot more it causes exhaust gas reversion up through the intake manifold and thus affecting carb signal and also the mixture as well. And cause of that it always requires a richer mixture vs a cam with less overlap.

Your cam has a lot more seat to seat duration vs my cam of 268/272 220/[email protected] 510/510 lift with a 114 LSA 42 degrees of overlap seat to seat in my 377 build.

Your cam you have has a easier ramp rate compared to mine which has a faster ramp rate and less duration from seat to seat thus less overlap vs yours even though mine in my 377 is only slightly different then yours @ 50 duration specs. Maybe someone else can chime in more in having experience by using the AFR gauge for setting up on the carb.
I get what you are saying about restricting the trans slot circuit. I hope I don't end up there. I really appreciate all the time you take working on my carb adventures. I wish I had your experience. I have never been happy with the way the left side trans slot is shaped at the bottom, it is a little angled instead of square. Also when the throttle blades are closed the right side exposes a little more slot than the left side. Twisted throttle shaft, bent butterfly, a miss on the machining, who knows, but it is there. About .010" worth. I have been tempted to go in there with something to even it up. But that kinda scares me. I'm pretty anal about some things, if you couldn't tell.

I had the car out for a short ride with the 28 IFR's and the 35 squirter. It runs good and strong. I am going to need more experience reading the gauge though. It seems it is all over the place when driving. It is hard to get to a steady state, but I am not getting any too lean readings. I need to drive it a lot more to get a better sense of what it is doing before I make any more changes. I can see where data logging could be advantageous.
I am going to call Chris Straub and have him verify the advertised duration of my cam. It is a pretty mild cam with no idle lope.
 

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I know exactly what your talking about on the transfer slot and they should be equal and believe it or not just about .010 can make a difference from one side to the other. I took a small saw blade with very fine teeth on one of mine that was like that and I was able to fix it no problem but I had to take my time and be vary careful with it and both sides look even now and no problems in how it looks. You have to understand that with a carburetor the numbers will never stay steady all the time as even with aftermarket fuel injection units that have the handheld monitors that you hook up to read real time date the numbers will constantly change and never stay steady at just one number with performance builds.
 

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Your car must be fairly light. Why so big on squirter‘s? Lesser throttle down time affects duration more than size of nozzle. Also a red or white cam is less aggressive. I would try smaller nozzle to see if it helps or hinders.

The transition slot passage hole in main body is .106” a brass sleeve or tubing with an .083”hole will make the over size transfer slot effectively like the old days. A bit of red Loctite will hold it in place.

Also the emulsion passages in the newer carburetors are too big and to many. Holes about .025” to .028” should be more than big enough. Depending on vacuum pull will determine if smaller is leaner or richer. But in my situation that range works best on the street on my car.

As was pointed out trial and error will get you there. I just read plugs to see the results.
 

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I have seen "transfer slot cut to different depths" as a recent topic somewhere, don't recall where it was, but it is a known issue with the current crop of baseplates.
i don't remember if it was just Holley or just Proform or some other source, or multiple sources. Correction was done with small dremel blade or small needle files.

might have been here...
racingfuelsystems.myfunforum.org - Index page

Racing Fuel Systems • View forum - Holley
 

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Discussion Starter · #15 ·
Your car must be fairly light. Why so big on squirter‘s? Lesser throttle down time affects duration more than size of nozzle. Also a red or white cam is less aggressive. I would try smaller nozzle to see if it helps or hinders.

The transition slot passage hole in main body is .106” a brass sleeve or tubing with an .083”hole will make the over size transfer slot effectively like the old days. A bit of red Loctite will hold it in place.

Also the emulsion passages in the newer carburetors are too big and to many. Holes about .025” to .028” should be more than big enough. Depending on vacuum pull will determine if smaller is leaner or richer. But in my situation that range works best on the street on my car.

As was pointed out trial and error will get you there. I just read plugs to see the results.
Yes, the car is very light. 2500# with me in it. The carb came stock with a 31 squirter. I have always fought an off idle bog with it. Originally cured it with a 35 squirter. After playing with it some more I found I could cure the stumble by richening the idle mix screws 1/8 turn. I then put the 31 back in it. It ran fine that way for a long time in the original stock engine. The new version of the engine had the same stumble so I put the 35 back in. I intend to try the 31 again with the AFR gauge now.
I hate changing squirters. I won't do it with the carb on the engine. I would have parts down in the manifold. IFR's and mains I change with the carb on, pretty quickly. But the squirter with the choke in the way is a PITA. Anybody have a good technique for changing squirters?
I've just started to get into the emulsion wells and air bleeds in the Vizard book. I get the concept, and am getting down to the details.
Yeah, trial and error is the method I will be using.:)
 

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Discussion Starter · #16 ·
I have seen "transfer slot cut to different depths" as a recent topic somewhere, don't recall where it was, but it is a known issue with the current crop of baseplates.
i don't remember if it was just Holley or just Proform or some other source, or multiple sources. Correction was done with small dremel blade or small needle files.

might have been here...
racingfuelsystems.myfunforum.org - Index page

Racing Fuel Systems • View forum - Holley
I think I can fix the irregularity of the transfer slots. Just have to find a file small enough to get in there.
I had not run across this website. It ought to be good for a lot of reading. I haven't found the thread about trans slot correction yet, but still looking. Thanks for the tip on the site.
 

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Just do a google search for holley transfer slot restrictor and you should come up with some information. As far as changing out your shooter goes and not getting anything in you engine I take a rag or paper towel and stuff it down underneath the boosters and vary carefully loosen the shooter screw then use a pair of needle nose pliers to grab it and take it out and make dang sure the bottom gasket does not fall into the intake and thus is the reason I put the rag or a paper towel into the carb to be underneath the shooter. I also put the shooter back in towards the side of it and not straight in as it is kind of tricky because of the choke plate being so close towards the shooter and you always hit the chole plate shaft and I go in towards the side with the two parts that stick out on the shooter that aligns up with the main body to keep it straight and have it angled towards the side then turn it towards the area where the shooter groove fits up against the main body to keep it straight and from turning. Here is a photo of a transfer slot restrictor mod.
615483
 

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Here is some info I found elsewhere. I am not saying do all this stuff but just read it and maybe you can pick up some information to help you out with your tuning with your wide band gauge.

I did a fair bit of WB tuning on the 3310 on my BBC truck and documented progress along the way here.

https://www.tapatalk.com/groups/rac...a-3310-with-a-secondary-power-valve-t960.html

Although I didn't try a TSR you might find some of the information useful.

With the amount of valve overlap your engine has the WB is not necessarily accurate at low speeds. The observed 14:1 AFR at idle is probably leaner than true AFR due to oxygen making its way into the exhaust during overlap. As you increase rpm and throttle the dilution effect is reduced. The true AFR may not be getting richer with RPM. The wideband is becoming more accurate. I mention this so you don't spend too much time chasing a number on the wideband. Give the engine what it wants.

At 2750 RPM the IFR still has some influence at very light throttle. I'd guess its insignificant when pulling a grade or accelerating. You were correct to reduce the MAB and increase the IAB to try and lean the cruise AFR in the 2,700 rpm range. You could also try reducing the emulsion bleeds in the primary metering block. These should be 0.028", and you can try 0.026". You might need to bump up the PVCRs to maintain WOT AFR. You might also need a higher # PV to keep from going too lean before the PV opens.

installing a TSJ might also work, but if you lean the top of the TS too much you might experience low speed bucking around town. I think its worth a try though.

After you get the low speed sorted out wire the secondaries shut and check WOT AFR on the primaries only and adjust PVCR to desired AFR. No need to run it to 6,000 rpm. A few short blasts in overdrive should do it. Reenable the secondaries and adjust secondary jetting to achieve desired WOT AFR.
 

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Discussion Starter · #19 ·
Here is where I am right now.
QFT SL-600-VS with Secondary Metering Block .....QFT 34-9
Idle Feed Restrictors ..... 28/28
Idle Mix Screws ..... 1/2 turn out
Curb Idle Screw ..... 3/8 turn in from contact (750 rpm idle)
Secondary Idle Screw ..... 1/4 turn in from contact
Transition Slot Exposure ..... about .030"
Squirter ...... 31
Main Jets ..... 68/74
Power Valve ..... 6.5
Power Valve Channel Restrictors ..... 52
Vacuum Secondary Opening ..... 1-1/2 turns out
Idle Air Bleeds ..... 70/70
Main Air Bleeds ..... 31/31
(All that has been changed from stock is the addition of the 34-9 secondary block, changed stock 31 IFRs to 28 all around, and changed secondary idle air bleeds from 39 to 70.)
Ignition Curve .....16 initial +18 mechanical (all in at 2700) + 16 vac (starts @ 7 inhg, all in @ 14 inhg)


Engine runs really good with this tune. Idles smooth. No off idle stumble. Cruise has no surging. No pinging under load. The only thing is the vacuum secondary opening needs adjusted as their is a very slight hesitation when the secondarys open up, but goes like hell when it passes thru the hesitation.

It wants to idle at 11.8 - 12.4 AFR @ 15 in hg in gear. Cruise at 14.5 - 15.2 AFR (once in a while it will venture into the 16 AFR range for a short bit) @ 16-17 in hg. @ 1800rpm. No sign of pinging. WOT drops to about 12.5-13 AFR.
I think I am really close. The only thing that disturbs me is the idle AFR. I would like to try to get the idle a little leaner, but my cruise AFR is already to the limit of what I want to take it. I don't know how to lean the idle without leaning the cruise AFR. I'm not sure if this is needed or not, but I would like to see for myself if it is. Here is a pic of the #1 plug after about a 20 minute drive and idle into the shop. Looks pretty rich to me, but I hate trying to read plugs with this current gasoline.
IMG_0773.JPG


I have been running 93 octane.
Vizard says to set the TS at about .050 to start with. I wonder if increasing TS exposure would lower the split to the idle port thereby leaning the idle. I would have to close the secondary idle screw if I did that. It is already at only 1/4 turn. The only other way would be to somehow restrict the idle port. I don't want to do any mods that can't be undone....... yet.
Anyway, that's where I am now.
 

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JMHO, in theory at idle the TS (transition slot) above throttle blade portion is designed to be an additional air bleed to lean the idle mixture. If you expose more TS under throttle it will close the above portion more cutting off air and possibly starting the transition circuit adding more fuel making the idle richer not leaner.
 
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