Drilling Holes In Carb Throttle Plate Blades
- Thread starter 340inabbody
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The factory air bleed calibration of most "out of the box Holleys and carters starts deviating from calibration below 15hg. If your below 10hg its not sensitive enough to maintain calibration during idle under load.
If you speak with Ruggles, or reference his fuel circuit calibration charts you will find that below 15hg the idle down channel air bleed is opened up about .003 to increase the sensitivity along with the idle circuit metering orifice, which in your case is located in the metering block.
Considering that your engine is a "fixed parameter" what is your wide band telling you about your afr when its in drive? The reading will tell you which direction to go. Hence, pig rich+ idle bypass. Lean, Idle down channel calibration.
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Controllable with Idle Mixture 12.5 to 13
The factory air bleed does not 'fall off at 15" of hg'. The air bleeds, idle & main, are at atmospheric pressure.
Their purpose is to [a] add air to emulsify the fuel control the start/finish of that cct.
Their purpose is to [a] add air to emulsify the fuel control the start/finish of that cct.
Its rich I believe
My understanding would be to add some air bleed, but that's irreversible on a fixed bleed Holley. The "easy button" is Idle bypass to see if your afr leans out, say 14.~ range and the vacuum hg goes up a pinch, say 1-1.5 hg.
About 15 minutes work for an experiment: Say it gets you in the right direction, your next move would be recalibrate the air bleed. These folks https://allcarbs.com/?v=0b3b97fa6688 built me a pair of carbs with adjustable air bleeds and their tech answers the phone Like Ruggles.
Yep, What is your base altitude?
Look at it like this:
Holley started manufacturing the HP series of carburetors with removable air bleeds for a reason.
Then Edelbrock introduces a Holley clone with an adjustable Idle bypass circuit for a reason. Be patient, and make small adjustments to the idle bypass that lean out the AFR. then work on the idle circuit recalibration "once you have a grasp of the circuits function."
You'll be using something like this for the fixed air bleed if you choose:
Good luck!
This is simple and doesn't take a long winded response.
The engine needs enough airflow and fuel at idle to have a stable idle. Lumpy cams need a higher idle speed. If you uncover the transfer slots to get the idle where it needs to be, it will run rich, load up, etc. Add timing to get the idle up (often requires a distributor recurve to limit total advance). This allows the throttle blades to close back down. If you still don't have enough airflow with the throttles closed then you have to add more air. Sometimes this requires drilling holes. It's not a big deal.
If the torque converter is stock-ish and you have a lumpy cam, you can absolutely expect headaches. That problem won't go away. And you'll chase your tail and go crazy trying to get it worked out. That is likely the core culprit here.
Edit: We really need a sticky for cam/torque converter/gearing basics.
The engine needs enough airflow and fuel at idle to have a stable idle. Lumpy cams need a higher idle speed. If you uncover the transfer slots to get the idle where it needs to be, it will run rich, load up, etc. Add timing to get the idle up (often requires a distributor recurve to limit total advance). This allows the throttle blades to close back down. If you still don't have enough airflow with the throttles closed then you have to add more air. Sometimes this requires drilling holes. It's not a big deal.
If the torque converter is stock-ish and you have a lumpy cam, you can absolutely expect headaches. That problem won't go away. And you'll chase your tail and go crazy trying to get it worked out. That is likely the core culprit here.
Edit: We really need a sticky for cam/torque converter/gearing basics.
Inertia
Well-Known Member
I have a 1950's kit for working with fixed bleeds, requires epoxy and a Drill vise as above. and a known hole diameter, and inserts to adjust size to find proper bleed diameter.
I think this is what I’m fighting. But I have no cam specs and no reference to what torque converter is in there currently. So how will I go about determining what converter I should probably get?
TT5.9mag
Two atmospheres are better than one
You are not hearing detonation at idle. Promise. You need load for detonation.
Yea like mashing the throttle in high gear heading up a grade, things get a rattling then, detonation you can hear.
I think I need to throw in a loose converter just to help with the differential idle issue.
Inertia
Well-Known Member
OP
Go back to fundamentals.
Lotta stuff mentioned here are far beyond what you likely need.
I've never had to drill holes in throttle plates when there are many ways to introduce air, including opening the secondaries a tad, or messing with PCV volumes.
Go back, way back, and start from scratch.
jmo, but this has kinda gone off the rails.
Go back to fundamentals.
Lotta stuff mentioned here are far beyond what you likely need.
I've never had to drill holes in throttle plates when there are many ways to introduce air, including opening the secondaries a tad, or messing with PCV volumes.
Go back, way back, and start from scratch.
jmo, but this has kinda gone off the rails.
That’s what I was doing, and when that thing is fully soaked with heat, the idle in gear is horrible. The idol is very bad it cold when it’s in gear as well.
If it has 4 corner idle you can't just open up the secondary butterflies.
Good question.
You can figure this out, pretty closely, without getting too scientific. But you basically need to learn the basics of degreeing a cam. But with a degree wheel and a dial indicator with an extended tip, you could figure out intake duration without pulling the intake.
If you have a solid cam you could do it without pulling the rocker arms.
If you can get us the approximate duration @50 lift we could make a reasonable suggestion on TC stall.
TT5.9mag
Two atmospheres are better than one
You can if you know where the secondary transfer slots are and if they need a restrictor.
TT5.9mag
Two atmospheres are better than one
This is when you should be tuning it.
I should've been clearer.
glhs0426
Well-Known Member
You have the Progression Ignition? Great product in my opinion. To help the neutral to drive RPM drop I have increased the in gear load area of the timing map. You may have also adjust the timing table breaks in Load and RPM breaks (X & Y) to get more resolution in your trouble area.
Obviously your combination will need totally different values than the one pictured.
Fix the "something changed" first.
This is very helpful. This is exactly what I did that no longer seems to work. I raised the timing just as you did so it would idle up a bit with increased timing when in gear. I got it within 200 rpm. But what changed I am not sure yet. I have a hunch. Thanks for sharing your map. It helps to see what other guys are doing. Yes this distributor is really helpful and works well.
Guys thanks for all the help here! I believe I was able to get the best idle I could given the motor set up. Your help is greatly appreciated!
I swapped carbs from my Holley 2 corner double pumper with mechanical secondaries 650 which was requiring more air past the transfer slot optimum opening with a 750 4 corner vacuum secondary that I had on my shelf. The 750 was enough for me to tune the idle without needing additional air at idle and hence maintain proper T slot opening.
I was able to get the idle to about 1100rpm out of gear and about 950 in gear. I used both vacuum signal and WBO2 sensing. She is idling at 13.6 AFR and 10-11Hg max. She will not run well below 950rpm in gear. She gets way too rough. All 4 air fuel mixture screws are sensitive and work well again telling me the T slot is in a good spot.
I have never seen vacuum higher than 11-12. I also tweaked the Kick-down linkage a little which I believe helped with in gear loading.
All in all I believe that this idle is as good as I can make it and it’s acceptable. Given the engine was optimized for a 4 speed set up and high static compression I doubt it would ever be much better without cutting the pistons and re-caming it.
Comments?
BTW I will report back on the next level of tuning as I believe it’s leaning out under higher levels of acceleration. With that I need to data log it which I never done yet and I need to buy an old laptop to do it.
I swapped carbs from my Holley 2 corner double pumper with mechanical secondaries 650 which was requiring more air past the transfer slot optimum opening with a 750 4 corner vacuum secondary that I had on my shelf. The 750 was enough for me to tune the idle without needing additional air at idle and hence maintain proper T slot opening.
I was able to get the idle to about 1100rpm out of gear and about 950 in gear. I used both vacuum signal and WBO2 sensing. She is idling at 13.6 AFR and 10-11Hg max. She will not run well below 950rpm in gear. She gets way too rough. All 4 air fuel mixture screws are sensitive and work well again telling me the T slot is in a good spot.
I have never seen vacuum higher than 11-12. I also tweaked the Kick-down linkage a little which I believe helped with in gear loading.
All in all I believe that this idle is as good as I can make it and it’s acceptable. Given the engine was optimized for a 4 speed set up and high static compression I doubt it would ever be much better without cutting the pistons and re-caming it.
Comments?
BTW I will report back on the next level of tuning as I believe it’s leaning out under higher levels of acceleration. With that I need to data log it which I never done yet and I need to buy an old laptop to do it.
Thanks for the feedback. Your making some good progress.
MobileCustoms
You can twist perceptions, reality won't budge
Make sure you get 2 return springs on that throttle linkage to avoid a stuck wide one throttle if the one breaks!
Thank you yes I put another one on it but they are not equal. So good reminder to revisit this.
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