AFR was 12.5 WOT, now 13.3

[threewood]

Had the carb apart (Edelbrock Thunder 800cfm) not to long ago, reset float level, new accelerator pump. Have a six pack hood sealed to the air cleaner. Just got a new in tank 255lph pump, new regulator set to 6psi.

I was getting a lean pop at off idle, partial throttle afrs in the 15.5 to 16.2afr so I swapped in thinner 2 stages richer rods for the primary, fixed the lean pop but now I noticed my wot AFR is 13.3ish.

It's not a big issue to swap up a few sizes on the secondary jets, but was curious to the cause.

Idle is fine, vacuum around 15in/hg, no vacuum leaks that I can find up top. Would colder temps require a more rich mixture? I thought about maybe an intake manifold leak?

 

[beanhead]

Yes on colder temps wanting more fuel, but if the change ocurred exactly when you did the rod swap, is it possible that it altered the entire mixture curve a little and you need to tune the WOT mix again? Just a thought.. (everything must work together in harmony, all that stuff..) I would think a vacuum leak would affect the idle and low-rpm more noticeably.

 

[biomedtechguy]

I am giddy with anticipation of wonderful tuning capabilities never had before once I get my Innovative Motorsports dual wideband O2 system installed.

I noticed my wot AFR is 13.3ish

How are you getting your A/F ratio data?

 

[threewood]

Yes on colder temps wanting more fuel, but if the change ocurred exactly when you did the rod swap, is it possible that it altered the entire mixture curve a little and you need to tune the WOT mix again? Just a thought.. (everything must work together in harmony, all that stuff..) I would think a vacuum leak would affect the idle and low-rpm more noticeably.

I cannot say for certain that it happened at the same time I swapped rods. But I think both primary and secondary going leaner are related. I'll swap in some fatter secondary jets and see how it acts. I did have to open the idle a/f mix more rich so it starts easier in the colder weather.

 

[threewood]

I am giddy with anticipation of wonderful tuning capabilities never had before once I get my Innovative Motorsports dual wideband O2 system installed.

How are you getting your A/F ratio data?

I have a wide band O2 sensor and a/f gauge installed. It has logging capabilities but I just observe what it does real time.

 

[biomedtechguy]

I have a wide band O2 sensor and a/f gauge installed. It has logging capabilities but I just observe what it does real time.

Thanks threewood. Good luck!

 

[69 GTX]

Corrected air can vary 1-2000 feet a day with humidity & baraometer & temp. So it could just be the seasonal change.

 

[threewood]

Corrected air can vary 1-2000 feet a day with humidity & baraometer & temp. So it could just be the seasonal change.

Hope that's it. I swapped in a bigger set of secondary jets but haven't had a chance to see wot a/f yet.

 

[biomedtechguy]

Corrected air can vary 1-2000 feet a day with humidity & baraometer & temp. So it could just be the seasonal change.

Speaking of...
I live in the swamps of Louisiana. Actually, although that is true, being north of a major lake means lower overnight temperatures, and possibly lower humidity. The track I go to has a similar atmosphere, located not too far but not that close to the Gulf of Mexico.
Anyway, since I am soon to have my Innovative Motorsports dual wideband O2 system installed, and I am already dealing with (or actually need to make time to deal with) carburetor problems since my 3x2 Holley carbs came back from Promax, is there a good online source or maybe even an app to help me understand atmospheric effects and how that may affect my tuning?
Thanks for any replies!

 

[beanhead]

Speaking of...
I live in the swamps of Louisiana. Actually, although that is true, being north of a major lake means lower overnight temperatures, and possibly lower humidity. The track I go to has a similar atmosphere, located not too far but not that close to the Gulf of Mexico.
Anyway, since I am soon to have my Innovative Motorsports dual wideband O2 system installed, and I am already dealing with (or actually need to make time to deal with) carburetor problems since my 3x2 Holley carbs came back from Promax, is there a good online source or maybe even an app to help me understand atmospheric effects and how that may affect my tuning?
Thanks for any replies!

Bio I bet the gurus on the racer's hangout could help out with that, I see them discussing that stuff all the time, calculating corrected atmosphere etc..

 

[Belle66]

After hitting the right AFR number, I still had to read the plugs to get the timing and fuel just right.

 

[biomedtechguy]

After hitting the right AFR number, I still had to read the plugs to get the timing and fuel just right.

I am hoping to garner the majority of the information I need from the gauges and data, along with the butt dyno.
I do use Autolite spark plugs because Don at FBO aka 4 seconds flat who is the man behind my current ignition system can read those specific spark plugs, and both he and my local engine builder who did the 4 bolt main 421 Tripower GTO recommend them.

 

[69 GTX]

I'm sure there's a app out there. All you need is barometric pressure, temp, & humidity, if I remember correctly. That'll give you an idea. Just use it as a reference. So in the spring if the air is cool, low humidity, & a high pressure front comes through you could be in the 0-500 feet of corrected altitude. Even though my actual elevation at home is 950ish. No come august when it's 90, & 70% humidity the corrected # might be 2-3000 feet. Given that Holley says for reference that 1 jet size is good for 2000 feet you can see how much the weather can change your tune.
So with that said I have a theory that I'm going to try. I'm going to try to run gas without any ethanol when the weather is at it's best. No ethanol in the gas should give the richest AFR. Then in the times between cool & blazing hot I plan to run the 10% blended, and 20% in August when it's the worst. This is just a theory on my part so until I can try it I can't confirm it. Also if you do run blended fuels the ratio I have heard also goes up during winter months which also might cause a leaner AFR. Again this is just all theory on my part till I can prove it.

 

[383man]

When you changed the metering rods were they thinner all around. I only ask because the very bottom of the rod is in the jet at low vacuum at WOT. Its been a while since I fooled with them but I would mike the rods at the very bottom and compare to the ones you took out. It could be thinner higher up where the rod runs at idle and part throttle but not the bottom. I don't remember if you can get metering rods like that or do they just make the rod thinner the whole lenth ? Many years ago we would file part of the metering rods to modify say part throttle so we would file the center of the rod and leave the bottom alone if we did not want to change full throttle (WOT) or we would file just the bottom some for a richer WOT mixture. And of course as was said the temps will make a difference in the mixture since cool air is heavier. Good luck with it. Ron

 

[biomedtechguy]

Wow...filing different areas of the metering rods...
So much about really being able to tweak carbs that I may never know!
I did just receive the highly recommended "How to Super Tune and Modify Holley Carburetors" so maybe that will help me out with my 3x2 Holley system.

 

[threewood]

The rods are stepped. When at high vacuum, the thicker part of the rod is in the jet. When they pop up due to reduced vacuum the thinner tip is in the jet = less restriction, more fuel. I have a calibration kit so I have several to choose from without needing to file them down.

 

[biomedtechguy]

Man, I have so much to learn.
Have any of you read this book?
If yes, will it help me wrap my head around carbs enough to help me understand how to tweak my Promax modded Holley carbs?

 

[69 GTX]

I'm in no way a expert, but all Holley's work similar so I would think if you learn the basics you'll be god to go.

 

[68 HEMI GTS]

Man, I have so much to learn.
Have any of you read this book?
If yes, will it help me wrap my head around carbs enough to help me understand how to tweak my Promax modded Holley carbs?
View attachment 690641

I have it, covers some basic stuff. Doesn’t really dive into the small details. Once you have the O2 sensor in you just gotta man up and start trying stuff. You can read till your blue in the face but I’ve learned a ton from making a change and driving. Also just studying how the circuits in the carb are set up are a weath of knowledge. That’s why I laugh when all the experts want to tie normal PV operation to idle and low speed A/f readings. And let’s be honest, there’s only so much to be tweak on a stock set of 6 pack carbs. My first step would be to order two secondary spring kits if you don’t have them already.

 

[biomedtechguy]

My first step would be to order two secondary spring kits if you don’t have them already.

Promax didn't touch my secondary springs, and before they modded OTHER parts of my carbs, the outboard carbs ALWAYS, under ALL circumstances, EVERY time worked flawlessly!