Carb tuning

[sixty9cobra]

I want to learn more about carburetors. Where can I find some info on fuel mixture besides jetting. My car runs good but the air fuel guage is all over the place. I have 13.5 idling, 11.0 between 2000 and 3000 and 13-14 all the way up to 6500. I was thinking of going fuel injection but reading the Holley and Fitech forum it seems to be ht or miss.

[My427stang]

I want to learn more about carburetors. Where can I find some info on fuel mixture besides jetting. My car runs good but the air fuel guage is all over the place. I have 13.5 idling, 11.0 between 2000 and 3000 and 13-14 all the way up to 6500. I was thinking of going fuel injection but reading the Holley and Fitech forum it seems to be ht or miss.

There are a few SA Books that can talk about the circuits and what to do, but in the end, it takes some experience to get to be effective doing it.

First I will say that if you always chase AF mixture, you'll always chase it and likely make yourself crazy.   A single engine doesn't always want the same number and all engines don't all want the same number.  Generally the best thing to do is to focus on the behavior and see if the numbers help you figure it out

That being said, for a MUCH simplified discussion

jets (idle fuel restriction, power valve restriction, and main jets) determine the amount of fuel (bigger = more, smaller = less)
air bleeds determine the timing of fuel (bigger equals later, smaller equals sooner).  Think hole in a soda straw, harder to get your root beer

Your idle seems fine, but when you crack the throttle you are going rich, that could be transition fuel or it could be too much jet, depending on how you got to 2000-3000 (open throttle or partially open), or more likely you could just be seeing your accelerator pump if it's when you hammer it

As far as when you are climbing, it's close but likely a smidge little on the lean side if you are at WOT. Like a jet size or two. 

You are in pretty good shape compared to many, as I said chasing a number is very difficult

[Drew Pojedinec]

Your idle seems fine, but when you crack the throttle you are going rich, that could be transition fuel or it could be too much jet, depending on how you got to 2000-3000 (open throttle or partially open),

Can also be due to how the initial booster flow begins.

[sixty9cobra]

I was trying to keep it simple but If I lean on it hard under 3000 I get a sneeze out of the carb once n a while hot or cold. Like retarded timing or a bad valve spring.Timing is loicked at 35 deg. I also see real lean numbers when I crack the secondaries this might be normal I don't know. This all cruising light to medium throttle. Its a 700 lift cam 303 duration so I expect it to be lazy downstairs. I went from 80s to 76 in the primary and it ran terrible and was way to lean so I went back to 80 primary and 88 secondaries. This motor pulls so hard its hard to crack the secondaries and not be sitting on the rev limiter in 2 seconds.

[Drew Pojedinec]

What carb list number, and post up calibration.

[sixty9cobra]

Ill have to get a look a the carb its a Holley hp850 where do I find the calibration info?

[Falcon67]

https://documents.holley.com/techlibrary_carb_numerical_listing.pdf

[Ford428CJ]

Part of the problem is having a locked out distributor on a street driven car. You’re better off to be running off the mechanical advance to get you there. JMHO

[6667fan]

Focus on the three things that happen most often. Idle, cruise and to a lesser degree WOT. Like Ross said if you pay attention to A/F at every rpm, in every range, you will possibly drive yourself crazy. The transition from one system in the carb to another may not be smooth and is more difficult to dial in. But, it is only a transition so it is not lasting. Apply your energy to having a lean idle A/F, a number at your common cruising rpm in top gear that is in the middle and a fat enough number at WOT that leaves no doubt you are allowing the engine enough fuel to make all the power it can.

Having said that it is important not to tune for a number as much as tune for what your combo likes. You could make your idle very lean and the engine might be struggling. ( you have some challenges with that cam at idle and getting into cruise but you have accepted that which will save you some angst).
When you are cruising and you lift the throttle you will see it go lean as it starts to drop back to the idle circuit. Don’t fret over it, as soon as you, (easily), put your foot back into it to get back to your regular cruise speed the A/F will revert to the range you established.

Because you like to put your foot into that motor I would get that WOT number all the way to 12.5. See how she pulls with new plugs, do two banzai runs,  then cut a plug open to read the porcelain down deep.

Let us know how it goes.
JB