I tested OEM springs cut to 90mm (when the spring is cut a slight down-bend is helpful at the cut end to help it seat at the cap).
It now accelerates HARD, & the stability is acceptable, with the balance tipping slightly to response.
This tells me the optimal spring length with the 2.8mm slide air port is in the 90mm - 94mm (free length) OAL range, with modified new OEM springs.
For reference, my current setup is an 07 SM, TPUSA 813 cams, long TORS, Uni UP 4229 pods, 150 mains, OEM springs cut to 90mm OAL, polished & chamfered slides, slide air ports drilled to 2.8mm, TBS needles no shims, 45 pilots, TPUSA +3 ignitor remap/8250 limiter, IX plugs.
I think I'm going to run it like this for awhile. The optimal OAL spring length may be 92mm, perhaps I'll give that a go.
TIP: if you cut the springs, make sure that you give the free cut end a small down-bend. Two smaller needle nose pliers will help you get that bend.
Bonus TIP: My measurements were taken with new OEM replacement springs; compression springs such as these may or may not take a "set" over time.
I have Chevy 605 long cannons ready to install (thanks Don), however I'm going to hold off on that install until I can get the bike back on the dyno & see what my carb tuning hath wrought...
