As you may know from other posts I run a wide-band A/F meter, which provides me with real-time feedback in actual on-road conditions.
I have tested various combinations of jets, needles, & shims in my 865/270. That said, my current setup is: 07 865/270; TPUSA +3/8250 reprogrammed Gill Igniter; TPUSA 813 cams; tuned CVK carbs (a/k/a “carbies†for our Aussie friends), with polished & chamfered slides, 2.8mm air port, OEM slide springs cut to 94mm OAL & clipped end bent to 92mm OAL, 18mm float height, 45 pilots, pilot screws 1 turn out, N3RF needles - no shims, 150 mains, TPS connected; UP4229 pods; NGK IX plugs: long TORS. My bike normally operates 400’ to 1500’ ASL.
I’ve tested just about every main jet combo from 145 thru 160 (with never a need to try smaller or larger); NBZY, NAGB, NBZT, & N3RF needles, with various shim combos; & various slide spring rate & length combinations.
The bottom line is that CVK carb circuits are complimentary, not mutually exclusive. The main selected will have a bearing on the needle performance, & pilot size will impact screw settings, float height will influence pilot size & screw settings, & airbox elimination will influence air port &/or slide spring rate/length. That’s just for starters.
With the stock 865/270 cams I really liked the NBZT needles. I could not, however, get them to work & play well with the TPUSA 813 cams. The NBZT needles ran rich in the middle (4k – 6k range) & that could not be improved without also destroying the top end A/F ratio ( that is, running too-small mains). The N3RF needles are similar in profile to the NBZT needles, however the N3RF needles are longer. The N3RF is the best needle that I have tried with the 813 cams on my bike.
When I ran the stock cams the smallest mains I ran were 145’s, & at that they ran lean, even with the crappy stock 865/270 cams. As a general rule stock-cammed CVK-carb’d 865/270’s tend to run rich near/at the limiter, presuming proper tuning; 813-cammed CVK carb’d 865/270’s, however, stay linear at the limiter if properly tuned (& that limit is higher with a reprogrammed or programmable igniter!).
Staffo, my opinion is that your bike currently needs the small 140 mains to get the midrange right with the NBZT needles you are currently running. Those needles run the richest of any of the above referenced. I think you would do better with a 145 – 148 – 150 main size range & N3RF needles, personally. In other words, the top end is compromised on the lean side in order to get a satisfying midrange, where you arguably spend most of the time running anyhow.
If, however, you had a wide-band A/F meter on-board, I think you would see that the top end is most likely running lean @ WOT with the 140 mains, & you are leaving power on the table, even with the poor-performing stock 865/270 cams.
As a general rule the 865/270 will run “OK†with overly rich mains, however, mains that are too large will sap torque & thereby suppress power. Most shade-tree tuners seem to run mains that are too big, & don’t understand how the carb circuits work together, or what order to tune them in to achieve maximum overall effectiveness.
