Main jets upper & Lower

[steveho]

Hi, simple question which I am embarrassed to ask…
As stock, why are larger air jets used for the upper cylinders to give a weaker mixture than the lowers?
It seems that with non-stock carbs, most folks end up with larger main jets (typically 1 size) on the lower cylinders, to presumably get the same effect.
Why do the upper cylinders ‘need’ a weaker mixture? It can’t be for reliability reasons as the uppers typically run hotter, so would generally benefit from a richer set-up, not weaker. I don’t get this!
Cheers.

[RZMech]

I am confused by your question,

A larger jet does not give a "weaker" (leaner) mixture, it gives a stronger (richer) mixture

[steveho]

Sorry, but my first question is why larger AIR jets are used for the upper/rear cylinders to give a weaker mixture. Not fuel jets, but these are/can also be used to give weaker mixtures for these cylinders.
A small detail but are critical to my overall question as to why the rear cylinders generally have weaker mixtures?

[Luther]

Hi Steve, yeah thats a good question. I would initially think that the lower more modern case fed cylinders would have a stronger signal to the carbs and have leaner jets but thats not what they did. I do want to point out the stock carbs have a pilot idle air circuit not connected to the needle jet. Theres another circuit with same size air jet for larger throttle openings. Im running 10 bigger main jets on the rear for safety sake so its interesting you say some folks are staggering the other way. I'm sure more 500's are being tracked on your side of the pond so more information gathered