Primary and secondary jets

[dodj]

When I change the primary jets, should I be changing the secondary jets the same amount?
Like if the primaries are dropped from 80 to 76, should the secondaries be dropped four sizes as well to maintain the same relationship?

[Chryco Psycho]

Often yes , but they work differently , front jets are more for cruise , rear are WOT so they can be different ratio . so the front might change more or less than the rear jetting

[dodj]

OK.  I have been reading various 'tuning' articles and a few mentioned keeping the carb 'square' .  The writer went on to talk about changing the secondaries when you change the primaries. I was not  really following his logic though.

I have one other tuning question though. When at cruise, if I just let off the throttle, it goes way lean, and sometimes dies. If I let the throttle off slowly, I'm OK.   What's not working as it should?

[RUNCHARGER]

Keeping it square involves math if it is an AFB or an AVS. If it is a Holley just go up or down the same amount of jet sizes and you'll be pretty close.
If it has metering rods you have to do the math to figure jet area minus rod displacement in power circuit and jump the secondary up or down the same percentage. When you're doing dual AFB's with staggered jetting on a stock Hemi manifold it gets interesting.

[Chryco Psycho]

I would start with getting all the jets down by the same amount if the primaries are rich likely the rear will be also at least it is a good starting point + it is difficult to tune the secondaries as you have to do  WOT Pull for a few seconds shut off & check the color  or better if you have an O2 sensor

[dodj]

It's a quick fuel 850DP. I'm running an MTX-L o2 sensor.
13.6- 13.8 idle.
13.8 cruise. After dropping from 80 to 76 main jets
WOT it actually goes to 14-14.3
There is no stumble when stepping on it. I'm a little concerned about it going leaner when stepping on it but more concerned about the engine going really lean (19.0+ to off scale) when letting off the throttle
and sometimes causing a stall.

[Chryco Psycho]

DRopping the throttle closed fast upsets every circuit in the carb , [almost, anyway]
the power valve slams shut if it is open , the fuel stops entering the airstream through the boosters , the air flow is still getting in a little past the throttle plates but you only have the idle slots feeding fuel ...
When you roll off slow the intake vacuum does transition from 0-2" to 18" immediately so the power valve can still supply fuel as the vacuum rises & the jets / boosters still add fuel until the throttle plates are almost closed .
Increasing the power valve closer to the idle vacuum reading in gear [if Auto] so if you have 10" you could move up to 8" PV .