B02S4
Learned Hand
Reged: 02/28/08
Posts: 1539
Loc: USA
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I've been experimenting with different spring rates & slide configurations, with the theory that running pod filters (in my case Uni UP4229's) reduces the vacuum demand & therefore lighter springs can be run.
Here are some preliminary thoughts:
OEM springs are too heavy & make for lazy throttle opening.
The Kawasaki GPZ springs are too light; the slides open too fast.
Stretched GPZ springs work better than stock GPZ springs, but are not optimal.
Yamaha FZ1 springs (made for a 37mm Mikuni) work better than stretched GPZ springs.
OEM springs clipped 9mm improve the low end, but the spring rate is too high above 5k.
The OEM slide opening (approx. 2.5mm) is sufficient with the FZ1 springs. Drilling the opening out to 2.8mm is too much with the FZ1 springs.
Still experimenting, so stay tuned... 
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gilligan
Adjunct
Reged: 04/23/07
Posts: 284
Loc: CT
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I cut my stock springs down ever so slightly (9mm sounds about right) and it did help the initial throttle response. Be careful not to cut too much - a little goes a long way.
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mag10
Adjunct
Reged: 01/16/08
Posts: 575
Loc: Wisconsin
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my best throttle response speed with the CVK carbs was drilled 3mm and the stock spring and the shrouding for the atmosphere side of the diaphragm removed (sort of like porting the carb).
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05 speedmaster - 904cc, 12:1 JE racing pistons, thunderbike cams, ported and polished head, scepter pipes, blueprinted manifolds, 39mm FCR's
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B02S4
Learned Hand
Reged: 02/28/08
Posts: 1539
Loc: USA
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Quote:
my best throttle response speed with the CVK carbs was drilled 3mm and the stock spring and the shrouding for the atmosphere side of the diaphragm removed (sort of like porting the carb).
Thanks for that. I'm going to stay at 2.8mm & try it with -12mm & -9mm OEM springs.
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B02S4
Learned Hand
Reged: 02/28/08
Posts: 1539
Loc: USA
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Quote:
...I'm going to stay at 2.8mm & try it with -12mm & -9mm OEM springs.
I tested the 2.8mm slides with the -9mm (approx. 94mm OAL) chopped OEM springs. Much better stability with acceptable response. I'm still going to try a -12mm OEM spring in my quest to optimize the balance of response v. stability.
Different rate & length springs can effect the AFR at static openings, & not just a slide transitions.
With what I now know, the FZ1 springs are probably the way to go with pods & 2.5mm stock slides. That said, 2.8mm slides & OEM springs cut to the proper length may be even better...
I'm going to find out. 
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Keith
Stickman Yogi
Reged: 03/21/09
Posts: 11609
Loc: BC, Canada
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Quote:
Still experimenting, so stay tuned...
Good one!  And thanks for the post... I'm in learning mode.
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Live to love, love to live.
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TrOjAn
Adjunct
Reged: 07/04/07
Posts: 410
Loc: Basildon. Essex. UK
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Very informative.. Ill be watching this thread for any updates.. nearly winter here so there will be plenty of time for playing with the bike
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TrOjAn
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B02S4
Learned Hand
Reged: 02/28/08
Posts: 1539
Loc: USA
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I also beveled the front & rear edges of slide cutout & polished the slide body (hand polish with 800/1000/1500 grit autobody paper & Simichrome) when I drilled the 2.8mm air port. Whether or not any of that made any difference whatsoever I don't know, but it couldn't hurt.
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B02S4
Learned Hand
Reged: 02/28/08
Posts: 1539
Loc: USA
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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...
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B02S4
Learned Hand
Reged: 02/28/08
Posts: 1539
Loc: USA
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Quote:
my best throttle response speed with the CVK carbs was drilled 3mm and the stock spring and the shrouding for the atmosphere side of the diaphragm removed (sort of like porting the carb).
As a follow-up, was that with the 865 or 904? If it was the 904, the 904 big bore kit should have increased the vacuum demand on the stock CV carbs by at least a little bit all by itself, all other things equal, eh?
By "removing the shrouding" do you mean the shroud at 12 o'clock near the mouth of the inlet, upstream of the slide?
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