Leaning out

[dodj]

I have a 440 with a QF 850 mechanical.
When I let off the throttle, it leans out from 12-13.5 to 19.0-23.0. Occasionally stalling the motor.
Much worse when it is below normal operating temps.

Right now my idle is 13.0 on the recently calibrated AFR.
Cruise 13.5 - 14.5
Acell 10.5 - 12.0

For all you carb tuning guru's, how do i fix this? My QF 850 is very adjustable. I have a selection of jets and air bleeds and cams. I have played around with it and accel and cruise are great. But what do I do for the throttle "let" off lean out?

[Brads70]

Maybe try smaller on the high speed air bleeds? 

[Brads70]

https://www.holley.com/blog/post/carb_class_air_bleed_basics/#:~:text=Idle%20Air%20Bleed%3A&text=Air%20to%20be%20mixed%20with,due%20an%20incorrect%20idle%20bleed.

[Strawdawg]

You might check the throttle blade settings against the slot and assuming that is good, if Brad's idea did not work, I think I would try a bit smaller on the idle air bleeds.  Sounds like it is over transitioning to the idle state when you let off.... maybe

[dodj]

Ok. A couple questions to go with the air bleed suggestion. How many numbers at a time? A couple? And should I expect to have to play with the idle mixture screws after each air bleed change?

Sounds like it is over transitioning to the idle state when you let off.... maybe

If I back off the throttle nice and easy, it goes back to a nice idle no problems. If I just lift my foot quickly, that's when I have issues. Is that 'over transitioning'?

[Brads70]

I would say if you change the idle air bleeds then yes you will need to adjust the mixture screws. The high speed ones I don't think so.
What size does it come with " stock"  ? 30ish?   

https://www.summitracing.com/parts/qft-br-67245?seid=srese1&gclid=Cj0KCQjw4cOEBhDMARIsAA3XDRjnWKnLJGoXC18-Cj0F_dR4CfDg0fC0VFk2BV2YnU01gPZEJaiv0C4aAr89EALw_wcB



I'm cheap and just bought blanks and drilled them out myself. It takes a lot of time I found.  Love the QF carbs though. I opened up the "bleeds"? behind the power valve when playing with mine . I could see the difference with each change on the A/F ratio gauge , sure couldn't do that as easy on a standard Holley.....

Of course weather conditions changes things, I found I needed to fully warm up the engine before I made any changes.... 

Mine is the opposite of yours .... goes rich when I let off.... still not totally happy with mine yet but would rather drive it than mess with it more. Free time to play seems to be in short supply these days....

[Strawdawg]

That was my definition... But might not be the correct term. Might just try closing the needles some and see if it changes anything 

[dodj]

Specs

[dodj]

but would rather drive it than mess with it more. Free time to play seems to be in short supply these days....

Last year I would agree with you and have lived with my situation, tinkering with it every now and then..
But...

I retired three days ago and plan to do more 'messing with it' and driving it. 

Might as well...I can't go anywhere..lol

[Brads70]

but would rather drive it than mess with it more. Free time to play seems to be in short supply these days....

Last year I would agree with you and have lived with my situation, tinkering with it every now and then..
But...

I retired three days ago and plan to do more 'messing with it' and driving it. 

Might as well...I can't go anywhere..lol

Congrats on retirement! New project car on the horizon? 

[Brads70]

Just looked up mine to compare specs. Close on air bleed size. Crazy how much they have gone up in price ! Wow!  I think I paid about $600 USD  7-8 years ago....

https://www.summitracing.com/parts/qft-q-850-an

[dodj]

Crazy how much they have gone up in price ! Wow!  I think I paid about $600 USD  7-8 years ago....

Ya, I think I paid around $600. The price now would make a FI setup much more likely...

[Skdmark]

Crazy how much they have gone up in price ! Wow!  I think I paid about $600 USD  7-8 years ago....

Ya, I think I paid around $600. The price now would make a FI setup much more likely...

That's now in the ballpark for a Holly Stealth 4150 EFI
https://www.holley.com/products/fuel_systems/fuel_injection/sniper_efi/sniper_efi_stealth_4150/sniper_efi_stealth_4150/parts/550-872

Makes you wonder if they are trying to steer more customer's to EFI.

Good luck on your carb tuning and congrats on your retirement.

[RUNCHARGER]

Personal opinion but yeah, I know I'll never buy a new carburator again, ever.

[Chryco Psycho]

I would make a significant change to make sure it helps so maybe decrease the size by 4-5 on the idle bleed .so the vacuum has to pull in more fuel . Basically I agree with all of the advice above .
Congrats on retirement a lot of us are getting to that age now .