Carb tuning with a WB, after idle what next?
11-07-2009, 08:58 PM
#1
Carb tuning with a WB, after idle what next? Hi All,
Carb is a Holley #82751 HP750 mechanical secondary double pumper:
I spent an hour this morning getting my idle set right (well, as right as I could). From my original "vacuum gauge" tune of 10.8 AFR, I got it up to 13.6 AFR but it still won't idle under 1050 without stalling when put in gear or turning the wheels. I tried 4 different AFR's from 11.5 to 14.5 and none would idle down without the stalling, and that's with a 3600 PI Vig!
To get there, I ended up drilling out my primary idle bleeds from 0.071 to 0.080 and the secondary bleeds from 0.028 to 0.040. Even so, my primary idle screws are only 3/8 turn open and the secondary screws are 1/4 turn open. I'm thinking these LS motors are waaay different on tuning than the old school smallblocks. All this as done under no-load conditions. I notice when I blip the throttle, the AFR goes lean so I guess I'll be ordering some bigger squirters and cams.
So, how do I do the part throttle, cruise, and WOT? And what AFR's should I be looking for?
NOTE: One other thing, is the AFR supposed to be steady? Mine seems to fluctuate from 13.2 to 13.7 (again, idling).
Thanks!
Carb is a Holley #82751 HP750 mechanical secondary double pumper:
I spent an hour this morning getting my idle set right (well, as right as I could). From my original "vacuum gauge" tune of 10.8 AFR, I got it up to 13.6 AFR but it still won't idle under 1050 without stalling when put in gear or turning the wheels. I tried 4 different AFR's from 11.5 to 14.5 and none would idle down without the stalling, and that's with a 3600 PI Vig!
To get there, I ended up drilling out my primary idle bleeds from 0.071 to 0.080 and the secondary bleeds from 0.028 to 0.040. Even so, my primary idle screws are only 3/8 turn open and the secondary screws are 1/4 turn open. I'm thinking these LS motors are waaay different on tuning than the old school smallblocks. All this as done under no-load conditions. I notice when I blip the throttle, the AFR goes lean so I guess I'll be ordering some bigger squirters and cams.
So, how do I do the part throttle, cruise, and WOT? And what AFR's should I be looking for?
NOTE: One other thing, is the AFR supposed to be steady? Mine seems to fluctuate from 13.2 to 13.7 (again, idling).
Thanks!
Last edited by S10xGN; 11-07-2009 at 09:07 PM. Reason: added note...
11-07-2009, 10:20 PM
#2
set afr with it IN gear as should your vacuum readings be taken the same way 
afr always fluctuates on the wideband, also i'd recommend the 50cc pump shot for the front and start with a 35 squirter and work your way up as needed. Sounds like it wants more idle timing and that will help with lower idle rpm. Shoot for 22-24 ish IMO.
my curve is 12 degrees from 0-500rpm then it jumps as a straight line to 23 at idle, plus 8 more coming from the map sensor. Total timing is 28 for now, I never got to tune it but up to 36 degrees has been posted online.
afr always fluctuates on the wideband, also i'd recommend the 50cc pump shot for the front and start with a 35 squirter and work your way up as needed. Sounds like it wants more idle timing and that will help with lower idle rpm. Shoot for 22-24 ish IMO.
my curve is 12 degrees from 0-500rpm then it jumps as a straight line to 23 at idle, plus 8 more coming from the map sensor. Total timing is 28 for now, I never got to tune it but up to 36 degrees has been posted online.
11-08-2009, 07:37 AM
#4
your correct that the LS engine has diff req. than gen 1 motors, lol
using a single plane intake and large cam creates problems, dont know what you have
i have found the LS engines kind of like the green pump cam in the #1 hole, you prob have the pink one
first the sec side, you must have drilled out the hi sp a/b's, their the ones that small-big mistake, your gonna have to use huge jets to meke up for it, or hopefully their repl screw in a/b's(prob were closer to .031 orig?)
on the pri side, they do run a little rich, again cam/intake comes into play
was the carb a known good one when installed?
although i run a blowthru, i run it rich at an idle, around 13, and yes it jumps all around-i use an LC-1 on the d/s, and hook up an LM-1 on the pass side, and i notice the pass side runs close to 1 AFR diff at idle, prob due to mixing at idle, but get closer to each as RPM goes up
what is your idle vacume, i also noticed a P/V with a higher # can help a tip in under cruise-with the larger idle a/b, you may have a off idle or light cruise lean problem-double ck for a vacume leak, maybe try a little higher idle timing,
shouldnt be dying in gear, esp with a high stall-seems it wont take a load, esp when the P/S sees a load
if the throttle blades are open to far, your in the transfer slots, and fuel is starting to flow, making it richer
using a single plane intake and large cam creates problems, dont know what you have
i have found the LS engines kind of like the green pump cam in the #1 hole, you prob have the pink one
first the sec side, you must have drilled out the hi sp a/b's, their the ones that small-big mistake, your gonna have to use huge jets to meke up for it, or hopefully their repl screw in a/b's(prob were closer to .031 orig?)
on the pri side, they do run a little rich, again cam/intake comes into play
was the carb a known good one when installed?
although i run a blowthru, i run it rich at an idle, around 13, and yes it jumps all around-i use an LC-1 on the d/s, and hook up an LM-1 on the pass side, and i notice the pass side runs close to 1 AFR diff at idle, prob due to mixing at idle, but get closer to each as RPM goes up
what is your idle vacume, i also noticed a P/V with a higher # can help a tip in under cruise-with the larger idle a/b, you may have a off idle or light cruise lean problem-double ck for a vacume leak, maybe try a little higher idle timing,
shouldnt be dying in gear, esp with a high stall-seems it wont take a load, esp when the P/S sees a load
if the throttle blades are open to far, your in the transfer slots, and fuel is starting to flow, making it richer
11-08-2009, 11:30 AM
#5
set afr with it IN gear as should your vacuum readings be taken the same way
afr always fluctuates on the wideband, also i'd recommend the 50cc pump shot for the front and start with a 35 squirter and work your way up as needed. Sounds like it wants more idle timing and that will help with lower idle rpm. Shoot for 22-24 ish IMO.
my curve is 12 degrees from 0-500rpm then it jumps as a straight line to 23 at idle, plus 8 more coming from the map sensor. Total timing is 28 for now, I never got to tune it but up to 36 degrees has been posted online.
afr always fluctuates on the wideband, also i'd recommend the 50cc pump shot for the front and start with a 35 squirter and work your way up as needed. Sounds like it wants more idle timing and that will help with lower idle rpm. Shoot for 22-24 ish IMO.
my curve is 12 degrees from 0-500rpm then it jumps as a straight line to 23 at idle, plus 8 more coming from the map sensor. Total timing is 28 for now, I never got to tune it but up to 36 degrees has been posted online.
your correct that the LS engine has diff req. than gen 1 motors, lol
using a single plane intake and large cam creates problems, dont know what you have
i have found the LS engines kind of like the green pump cam in the #1 hole, you prob have the pink one
first the sec side, you must have drilled out the hi sp a/b's, their the ones that small-big mistake, your gonna have to use huge jets to meke up for it, or hopefully their repl screw in a/b's(prob were closer to .031 orig?)
on the pri side, they do run a little rich, again cam/intake comes into play
was the carb a known good one when installed?
although i run a blowthru, i run it rich at an idle, around 13, and yes it jumps all around-i use an LC-1 on the d/s, and hook up an LM-1 on the pass side, and i notice the pass side runs close to 1 AFR diff at idle, prob due to mixing at idle, but get closer to each as RPM goes up
what is your idle vacume, i also noticed a P/V with a higher # can help a tip in under cruise-with the larger idle a/b, you may have a off idle or light cruise lean problem-double ck for a vacume leak, maybe try a little higher idle timing,
shouldnt be dying in gear, esp with a high stall-seems it wont take a load, esp when the P/S sees a load
if the throttle blades are open to far, your in the transfer slots, and fuel is starting to flow, making it richer
using a single plane intake and large cam creates problems, dont know what you have
i have found the LS engines kind of like the green pump cam in the #1 hole, you prob have the pink one
first the sec side, you must have drilled out the hi sp a/b's, their the ones that small-big mistake, your gonna have to use huge jets to meke up for it, or hopefully their repl screw in a/b's(prob were closer to .031 orig?)
on the pri side, they do run a little rich, again cam/intake comes into play
was the carb a known good one when installed?
although i run a blowthru, i run it rich at an idle, around 13, and yes it jumps all around-i use an LC-1 on the d/s, and hook up an LM-1 on the pass side, and i notice the pass side runs close to 1 AFR diff at idle, prob due to mixing at idle, but get closer to each as RPM goes up
what is your idle vacume, i also noticed a P/V with a higher # can help a tip in under cruise-with the larger idle a/b, you may have a off idle or light cruise lean problem-double ck for a vacume leak, maybe try a little higher idle timing,
shouldnt be dying in gear, esp with a high stall-seems it wont take a load, esp when the P/S sees a load
if the throttle blades are open to far, your in the transfer slots, and fuel is starting to flow, making it richer
PRI main jets______75- - - - - - SEC main jets______80
PRI main bleeds____25 - - - - - -SEC main bleeds____36
PRI idle bleeds____71 - - - - - -SEC idle bleeds____28
PRI pump___________30cc- - - - - SEC pump___________30cc
PRI pump cam_______pink- - - - - SEC pump cam_______pink
PRI pump cam hole__1 - - - - - - SEC pump cam hole__1
PRI squirter_______0.031" - - - -SEC squirter_______0.028"
PRI power valve____4.5" - - - - -SEC power valve____n/a
Throttle blades are almost closed, in fact I had to remove the carb and close the secondary blades some to get any adjustment on the primary screw. In all fairness to the PS, I'm running +4.5° of caster. Enough so you can feel the front end lift when turning! Still doesn't seem like enough load to cause a stall, same as the converter. Also, my O2 bung is located in the "X" of my X-pipe and seeing both sides of the engine equally.
11-12-2009, 08:35 PM
#6
Well, I got to do some part-throttle driving today, the results of dialing out some fuel were amazing! It went from feeling like a low 14 second car to feeling like a low 12 second car. AFR at part-throttle was averaging around 14.4 - 14.8. Couldn't get a AFR read on any "punches" as I was by myself. I was seeing the AFR go lean under no-load "blips", couldn't tell if that was happening under load, but it sure didn't feel like it was.
Still idles like cr@p and wants to stall under any kind of load. The HP series doesn't have a choke, so I'm thinking of adding a 12V air horn solenoid to open up a small air bleed under the carb to raise the idle speed (which would require adding more idle fuel). What ya'll think???
Still idles like cr@p and wants to stall under any kind of load. The HP series doesn't have a choke, so I'm thinking of adding a 12V air horn solenoid to open up a small air bleed under the carb to raise the idle speed (which would require adding more idle fuel). What ya'll think???
11-18-2009, 07:57 PM
#7
D@mn, this is more like a blog than a forum but maybe someone will benefit from it...
Did some more WB tuning today with the laptop hooked up to the MSD box and managed to get a solid (hot) idle at 900 RPM's with 12.9 AFR and 14" vacuum. I have 45° advance at idle and should actually have 50° but found out later I have a "hard limit" of 45° max. That should be 34° of programmed timing plus 16° of MAP advance. The blue lines are where my idle is, I neglected to take a snap of it while running. Hopefully, I'll get to drive it tomorrow!
BTW, I tested my theory on the Holley main jet air bleed and found that using a #74 jet raises the idle speed to 1000 (13.3 AFR) and a #90 jet raises the idle to 1080 (14.0 AFR). If it wants to stall when cold, I'll add a small 12V solenoid and use the #90 jet to get the idle speed up so it won't stall...
Did some more WB tuning today with the laptop hooked up to the MSD box and managed to get a solid (hot) idle at 900 RPM's with 12.9 AFR and 14" vacuum. I have 45° advance at idle and should actually have 50° but found out later I have a "hard limit" of 45° max. That should be 34° of programmed timing plus 16° of MAP advance. The blue lines are where my idle is, I neglected to take a snap of it while running. Hopefully, I'll get to drive it tomorrow!
BTW, I tested my theory on the Holley main jet air bleed and found that using a #74 jet raises the idle speed to 1000 (13.3 AFR) and a #90 jet raises the idle to 1080 (14.0 AFR). If it wants to stall when cold, I'll add a small 12V solenoid and use the #90 jet to get the idle speed up so it won't stall...
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01-01-2010, 07:27 PM
#8
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I have been having the same probly with my 5.3. I am using a 750 vac secondary 30cc pump factory orange cam.Put in gear in slows down and wants to stall. I also had a bad bog and was getting a lean pop when taking off from a stop or WOT. After the bog it runs like a raped ape. I bought some pump cams and a 35 squirter. Most people are using a pink cam wich is the smallest one in the kit. Ran worse than the factory orange cam. I switched to the brown cam, largest cam. Helped it out alot but it still had a very slight bog but no stumbling one slow takeoff. I then pulled the brown cam for a blue cam, the second largest, and installed the 35 squirter. Perfect! no stumbling no bog. I then installed the largest cam again to see what happed and it gave a little too much gas and caused a rich sputter so returned the blue cam.
01-01-2010, 09:22 PM
#9
I got mine dialed in good (for now), but I just ordered the Proform body with annular boosters. I ended up adding the 50cc pump to the front, went up 4 numbers on both squirters (0.035 & 0.032), and went back to the 6.5 PV. Only problem I'm seeing now is the AFR drifting around at cruise speed. It goes from 13.8 to 18.0 and back with no apparent pattern. When I get the annular body in, I'll start over. 
01-18-2010, 08:14 AM
#10
The Innovate site has some pretty good articles on tuning with a wideband.
http://www.innovatemotorsports.com/r...rb-central.php
This one in particular answers your question of "what next"
http://www.innovatemotorsports.com/r...FI_mileage.php
Looks like you figured out these open plenum manifolds need a healty accelerator pump shot to get moving. I don't think it is the volume of it so much as getting it to move some gas with the initial touch of the throttle. I didn't have much luck with the pink cam. I am usign the brown one now, but will look into the blue one once the salt is off the road.
http://www.innovatemotorsports.com/r...rb-central.php
This one in particular answers your question of "what next"
http://www.innovatemotorsports.com/r...FI_mileage.php
Looks like you figured out these open plenum manifolds need a healty accelerator pump shot to get moving. I don't think it is the volume of it so much as getting it to move some gas with the initial touch of the throttle. I didn't have much luck with the pink cam. I am usign the brown one now, but will look into the blue one once the salt is off the road.
01-18-2010, 10:08 PM
#11
The Innovate site has some pretty good articles on tuning with a wideband.
http://www.innovatemotorsports.com/r...rb-central.php
This one in particular answers your question of "what next"
http://www.innovatemotorsports.com/r...FI_mileage.php
Looks like you figured out these open plenum manifolds need a healty accelerator pump shot to get moving. I don't think it is the volume of it so much as getting it to move some gas with the initial touch of the throttle. I didn't have much luck with the pink cam. I am usign the brown one now, but will look into the blue one once the salt is off the road.
http://www.innovatemotorsports.com/r...rb-central.php
This one in particular answers your question of "what next"
http://www.innovatemotorsports.com/r...FI_mileage.php
Looks like you figured out these open plenum manifolds need a healty accelerator pump shot to get moving. I don't think it is the volume of it so much as getting it to move some gas with the initial touch of the throttle. I didn't have much luck with the pink cam. I am usign the brown one now, but will look into the blue one once the salt is off the road.
I just got my WB installed as well so I'm going to be working on tuning my Edelbrock carb soon 