Any quickfuel carb Jetting guru's on here? I finally got around to installing an 02 sensor in my 505/512 stroker and got some readings at various loads. I am not a jetting expert and could use a second pair or 2 of eyes on my numbers and jetting choices.
Quickfuel carb tuning
- Thread starter MEV
- Start date
Are you running a Brawler race series or what are you running?
Dave
Dave
SS830
Knebel
Senior Member
What do you need to know? Whats your numbers?
70bigblockdodge
Old Man with a Hat
Jets will get you close. Air bleeds since you have easy changable ones will bring the fine tune in.
Best way to get it very spot on is to split carb in half, disconnect the secondaries and wire shut. Once the front side is right reconnect the secondaries and make them compliment the front side.
Best way to get it very spot on is to split carb in half, disconnect the secondaries and wire shut. Once the front side is right reconnect the secondaries and make them compliment the front side.
Other than the very rich condition, the carb is very good as is. It starts, idles, accelerates ferociously, and it makes good power as several of you have seen from my timeslips and videos. It is a STREET DRIVEN car.
Idle @800 RPM AFR 12.9
Steady state cruise at 35mph @ 2050 RPM AFR 10.6
Steady state cruise at 55mph @ 2500 RPM AFR 10.2-10.4
Steady state cruise at 65mph @ 2900 RPM AFR 10.3-10.5
Light acceleration, medium load AFR 10.2-10.5
WOT top gear AFR 12.9-13.4
The stock jet card is as follows.
Primary main jet 78
Secondary Jet 86
Idle air bleed 70/70
Hi speed bleed 28/28
Pri Nozzle 33
Sec Nozzle 35
Needle and seat 120
Power valve 6.5
a while ago i talked to quickfuel (before holley bought them) and they told me to change the high speed bleed, to lean it out some, i cannot remember what jets they told me to run, but i installed them.
Idle @800 RPM AFR 12.9
Steady state cruise at 35mph @ 2050 RPM AFR 10.6
Steady state cruise at 55mph @ 2500 RPM AFR 10.2-10.4
Steady state cruise at 65mph @ 2900 RPM AFR 10.3-10.5
Light acceleration, medium load AFR 10.2-10.5
WOT top gear AFR 12.9-13.4
The stock jet card is as follows.
Primary main jet 78
Secondary Jet 86
Idle air bleed 70/70
Hi speed bleed 28/28
Pri Nozzle 33
Sec Nozzle 35
Needle and seat 120
Power valve 6.5
a while ago i talked to quickfuel (before holley bought them) and they told me to change the high speed bleed, to lean it out some, i cannot remember what jets they told me to run, but i installed them.
I'm running a SS750. Primaries are 78's and secondaries are 84's.
In order to learn the "high speed" mixture, increase the size of the existing air bleeds for that circuit. Going smaller just makes it richer. Completely plugged = "full rich".
In general, set the primary main jet size for normal road cruising. Use the air bleeds to fine tune that circuit. Use the power valve for additional "WOT" fuel, rather than a larger main jet size, when possible. To me, that's just "good carb tuning", no matter what the carb might be.
The idle circuit looks pretty good, to me. Just need to get the main circuit dialed in for the "cruise" function. Ought to help piston ring and motor oil life, too!
CBODY67
In general, set the primary main jet size for normal road cruising. Use the air bleeds to fine tune that circuit. Use the power valve for additional "WOT" fuel, rather than a larger main jet size, when possible. To me, that's just "good carb tuning", no matter what the carb might be.
The idle circuit looks pretty good, to me. Just need to get the main circuit dialed in for the "cruise" function. Ought to help piston ring and motor oil life, too!
CBODY67
70bigblockdodge
Old Man with a Hat
What is your vacuum reading at all those steady state cruise?
I don't think bleeds are going to bring your cruise up to 14.5. Your WOT is slightly lean which will probably fatten up with secondary jet increase or a secondary bleed decrease. You need the steady state cruise to come in first and that will be on the primaries. Your power valve needs to be one half manifold vacuum to ensure it is not coming on at cruise/light throttle.
I don't think bleeds are going to bring your cruise up to 14.5. Your WOT is slightly lean which will probably fatten up with secondary jet increase or a secondary bleed decrease. You need the steady state cruise to come in first and that will be on the primaries. Your power valve needs to be one half manifold vacuum to ensure it is not coming on at cruise/light throttle.
No Vac gauge, only tach and handheld digital o2 meter.
70bigblockdodge
Old Man with a Hat
You will need a vacuum gauge ( cheap harbor freight works). In the meantime do you have any issue with your power brakes? Just trying to get a idea of where your idle vacuum is at.
Shooting from the hip I would say your power valve is opening at cruise, your probably a couple too big on primary and couple too small on secondary. Purely a guess.
Shooting from the hip I would say your power valve is opening at cruise, your probably a couple too big on primary and couple too small on secondary. Purely a guess.
Knebel
Senior Member
Honestly, except for wot that thing is pig rich.
First get a vacuum gauge and see what you are pulling at idle. devided that by 2 and thats your power valve value. Thats the first thing, get the correct powervalve. If its on the fence, get the next higher one. So if you pull 8" HG, get a 4.5" power valve.
Testdrive record AFR
Then I would start leaning out the idle a little to about 13:5 afr, see how that runs. Adjust idle mixture by slowly turning in one screw until the engine sounds choppy, the back out half a turn. Same with the other side then.
Testdrive, Record AFR
Then:
I would start on the primary side and put a 70 jet in it if it is still in the 10:1 range (the powervalve change could have already fixed this. Get closer to 14 afr cruise. going from 10:1 to 14:1 will require quite some downsizing. Cruise you can usually go upto 15:1 afr. Then see what your accel enrichment does, (lean off idle but everywhere else okay -12.7:1- ?). Report back on that pls. If you are rich off idle, thats okay we can address that later, if you backfire and you are lean, a tad smaller airbleeds fixes that or different nozzle or pumpcam.
When you lean out the primary side, your WOT will probably go leaner too on the secondaries. Dont touch those yet,better, disconnect and wire shut. Like said previously. Dial In the primary side first and only drive on those. Once that is dialed in, reconnect the secondaries and do WOT pulls. Lean, you now know you need bigger jets, way rich, you need to lean out the secondary jets.
ONLY DO ONE CHANGE AT A TIME AND TESTDRIVE AND RECORD AFR. Don't mess with airbleeds quite yet we'll get to that later... you can mess up a lot with them. This will be a lot if work but it will drive awesome after and will return decent economy without washing the oil from the cylinder walls.
First get a vacuum gauge and see what you are pulling at idle. devided that by 2 and thats your power valve value. Thats the first thing, get the correct powervalve. If its on the fence, get the next higher one. So if you pull 8" HG, get a 4.5" power valve.
Testdrive record AFR
Then I would start leaning out the idle a little to about 13:5 afr, see how that runs. Adjust idle mixture by slowly turning in one screw until the engine sounds choppy, the back out half a turn. Same with the other side then.
Testdrive, Record AFR
Then:
I would start on the primary side and put a 70 jet in it if it is still in the 10:1 range (the powervalve change could have already fixed this. Get closer to 14 afr cruise. going from 10:1 to 14:1 will require quite some downsizing. Cruise you can usually go upto 15:1 afr. Then see what your accel enrichment does, (lean off idle but everywhere else okay -12.7:1- ?). Report back on that pls. If you are rich off idle, thats okay we can address that later, if you backfire and you are lean, a tad smaller airbleeds fixes that or different nozzle or pumpcam.
When you lean out the primary side, your WOT will probably go leaner too on the secondaries. Dont touch those yet,better, disconnect and wire shut. Like said previously. Dial In the primary side first and only drive on those. Once that is dialed in, reconnect the secondaries and do WOT pulls. Lean, you now know you need bigger jets, way rich, you need to lean out the secondary jets.
ONLY DO ONE CHANGE AT A TIME AND TESTDRIVE AND RECORD AFR. Don't mess with airbleeds quite yet we'll get to that later... you can mess up a lot with them. This will be a lot if work but it will drive awesome after and will return decent economy without washing the oil from the cylinder walls.
I will get a longer piece of vac hose and test it cruising down the road, the idle and 2500 rpm no load numbers are:
Vacuum @ 850 RPM idle -10
@2500 RPM no load -15
65sporty
Old Man with a Hat
Sounds like these guys are pointing you in the right direction, correct carb tuning is a art. A carb like your quick fuel that has things like screw in air bleeds helps a lot.
With some older carbs that didn't have those features you drilled them out and hope you didn't go too big.
With some older carbs that didn't have those features you drilled them out and hope you didn't go too big.
70bigblockdodge
Old Man with a Hat
I'm going to guess your power valve is opening, because of 15" at no load 2500 rpm. The first change I would make is the old Holley rule of thumb, 1/2 the idle vacuum and use power valve just below that.
1/2 would be 5" so a 4.5" power valve should help. Getting the power valve to stay closed at cruise is the goal here, I believe that's why you are so fat at cruise, but not far off with WOT. Changing the power valve opening pressure will not affect the WOT so no need to really check that after change, unless you want to. Vacuum at cruise reading will be helpful.
Depending how much the cruise leans out with new PV, we can guess what to increase/ decrease to put cruise right, and fatten WOT up a bit.
Added bonus of this work will be better fuel economy on your 160 mile round trip to the strip. Not to mention, not wearing out your rings and cylinder wall with all that fuel washing.
Knebel
Senior Member
Hm. I was always under the impression to go to the next stiffer size powervalve...to be sure it only opens when you really want it to!? I guess as long as you are in the ballpark, it will be okay.
Also, how are the throttle blades adjusted? You have to have the transition slot showing just a tad or it will be off the idle circuit. Here is the thing with the airbleeds, you have a couple circuits that overlap:
Idle - transition slot (low speed and rpm cruise) - main jets
The transition slot mixture you can adjust a little leaner for under 2000rpm cruising if thats real fat, with airbleeds only go one or two sizes up/down, they have a huge effect. I used to adjust this so I would have 13:8 to 14.2 afr just off idle and below 2000. Then after that aproaching 15:1 with the actual main jets.
at 2500-3000 you should be in the main jets, thats where you do the actual jetting. They do have an effect on the lowspeed too but not as much because there is an overlap where you transition to the boosters.
this is really an art and lets say if you put smaller airbleeds in for the transition slot area, you will be dragging out that circuit to higher rpms. if you put in larger ones to make it leaner, you will shorten it (when it was fine til 2000rpm, you might see it go real lean starting at 1500 or 1800) this is then where you have to find the balance between all the bleeds and the mainjets.
does the SS carb have the metering block with the adjustable power valve orfices? Thats another factor where you can adjust rich/lean tipins. Its I pretty steep learning curve and requires a lit of testdriving. Also thats why I said change one thing at a time and test.
1- Check transitionslot showing
2- adjust idle afr like described (or go for highest stable idle vacuum)
3- put in correct power valve according to vacuum
4- accel pump off idle, make sure no backfires/stallig. Rich is fine for now tune that later
5- get 2500rpm cruising to a decent afr with mainjets
6- now you could see what the accel pump does with bigger/smaller nozzels and pumpcams
7- power valve offices, what happens when you are at 2500rpm cruising and you give it some gas, does it go a little rich or a little leaner than cruise afr? you can fix that by changing orfice sizes for the power circuit
8- once all this is done perfect, reconnect the secondaries and mash the throttle and see where your AFR goes, it it shoots up lean into 14...15..16, STOP and put in substantial bigger jets in the secondaries.
9 - mash the throttle and if you get 12.7:1 with the secondaries opening, you are done.
10- or proceed to the very fine tuning of the transients between circuits with airbleeds (they are not there to really adjust your AFR but the timing of the circuits, just keep that in mind)
Also, how are the throttle blades adjusted? You have to have the transition slot showing just a tad or it will be off the idle circuit. Here is the thing with the airbleeds, you have a couple circuits that overlap:
Idle - transition slot (low speed and rpm cruise) - main jets
The transition slot mixture you can adjust a little leaner for under 2000rpm cruising if thats real fat, with airbleeds only go one or two sizes up/down, they have a huge effect. I used to adjust this so I would have 13:8 to 14.2 afr just off idle and below 2000. Then after that aproaching 15:1 with the actual main jets.
at 2500-3000 you should be in the main jets, thats where you do the actual jetting. They do have an effect on the lowspeed too but not as much because there is an overlap where you transition to the boosters.
this is really an art and lets say if you put smaller airbleeds in for the transition slot area, you will be dragging out that circuit to higher rpms. if you put in larger ones to make it leaner, you will shorten it (when it was fine til 2000rpm, you might see it go real lean starting at 1500 or 1800) this is then where you have to find the balance between all the bleeds and the mainjets.
does the SS carb have the metering block with the adjustable power valve orfices? Thats another factor where you can adjust rich/lean tipins. Its I pretty steep learning curve and requires a lit of testdriving. Also thats why I said change one thing at a time and test.
1- Check transitionslot showing
2- adjust idle afr like described (or go for highest stable idle vacuum)
3- put in correct power valve according to vacuum
4- accel pump off idle, make sure no backfires/stallig. Rich is fine for now tune that later
5- get 2500rpm cruising to a decent afr with mainjets
6- now you could see what the accel pump does with bigger/smaller nozzels and pumpcams
7- power valve offices, what happens when you are at 2500rpm cruising and you give it some gas, does it go a little rich or a little leaner than cruise afr? you can fix that by changing orfice sizes for the power circuit
8- once all this is done perfect, reconnect the secondaries and mash the throttle and see where your AFR goes, it it shoots up lean into 14...15..16, STOP and put in substantial bigger jets in the secondaries.
9 - mash the throttle and if you get 12.7:1 with the secondaries opening, you are done.
10- or proceed to the very fine tuning of the transients between circuits with airbleeds (they are not there to really adjust your AFR but the timing of the circuits, just keep that in mind)
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70bigblockdodge
Old Man with a Hat
@Knebel His idle vacuum is low enough and no load cruise is not super either. I believe his power valve is open alot. Which in old Holley terms is raising his effective jets 6-10 sizes when it is open so add that to the 78s in his primaries he is in the neighborhood of mid to high eighties jet size for cruise circuit is way too much, reflected in the afr at cruise. The 4.5" hg power valve means the manifold vacuum has to go below 4.5" hg to have it open up. Keeping it closed will force afr to be on the main circuit only with a little extra from idle circuit till throttle passes 1/3 open. The power pistons work a little different on a Carter/Eddy moving the piston up to use smaller part of metering rod and enriching the afr.
I think if his power valve stays closed his cruise should fall right in at 13-14 :1 where he can enlarge the bleeds to lean it a tick more. Most drastic would be he drops a couple of sizes on primary main jets.
I'm pretty sure he has 4 corner idle circuit on that carb so no need to have the blades open far at all unless adjusted completely wrong. I've seen it done but I don't think he has changed it that much to get it that confused.
I think if his power valve stays closed his cruise should fall right in at 13-14 :1 where he can enlarge the bleeds to lean it a tick more. Most drastic would be he drops a couple of sizes on primary main jets.
I'm pretty sure he has 4 corner idle circuit on that carb so no need to have the blades open far at all unless adjusted completely wrong. I've seen it done but I don't think he has changed it that much to get it that confused.
Knebel
Senior Member
yes thats what I am saying too. Thats why I'm saying to do the correct valve first and then see where it lands. If the cruise is still 10:1 or something he can drop at least 10 jet sizes. But also, all the circuits interact with each other, so thats why testing that at a higher cruise rpm!
Put in a 4.5 holley power valve
Light cruise 2300 rpm Vac -15 AFR 10.5
Highway cruise 2700 rpm Vac -22.5 AFR 10.4
Moderate acceleration AFR 11.8
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