Main Jets

[dodj]

Messing around with my QFT 850 main jets. At what RPM are you pretty assured you are running on just the main jets?
The reason I ask is that I was at an AF of 12.6 at cruise with an 80 main jet. I dropped to 78 and it went to about 12.0-13.2. I then dropped to a 76 and it went to about 13.5-14.0. I then dropped to a 74 and the AF didn't change. So I was wondering if there is some other part of the carb coming into play? Secondaries? I was cruising at about 2300 rpm.

[Chryco Psycho]

if you at 1/3 throttle or less & the load is light / power valve closed only main jets & idle circuit should be in play , air bleeds will affect both circuits also

[dodj]

Ok thanks. Guess I'll start reading up on when and why of changing air bleeds

[Chryco Psycho]

if the air bleeds are too large you can install a piece of wire to reduce the size , if the car idles better you know the idle bleeds are too large , similar effect with jetting installing a piece of wire in the bleeds can make the jetting more accurate .
I use mig welding wire as a test , build a U shape & slide into both jets

[dodj]

I think I may need to go the other way. I have the idle mixture screws in between a half and 3/4 turns out to get a mixture at about 13.2-13.5.

[Chryco Psycho]

I would leave the idle bleeds alone then , the jet bleeds may be a different situation

[dodj]

I would leave the idle bleeds alone 

OK,
Just been reading as much as possible on tuning the QF 850 and there is a lot to digest!
Don't want to waste time changing adjusting what I don't need to but there is a lot of conflicting info out there.