B1200 MASSIVE mid throttle flat spot - help?

First topic message reminder :

Hi All, I've got an issue I've tried to tune out / fix for a few months now but I think Ill ask the collective knowledge base before I hurt my back anymore stooping over a bike.

The Bike...
2004 GSF1200S  36,000km
Slip on exhaust
K&N with 1.5" hole mod to airbox lid
PAIR system removed and plugged
17.5 pilot jets @ 3 turns out on the screws (have tried 2, 2.5, 3.5 and 4 turns out)
110 main jets
standard needles on lower most clip position
Standard slide springs but shortened free length by 20mm
New NGK JR9B plugs

What it does...

Quarter mile drags, great immediately off the line, wheelies easily but as soon as you get to approx 40% throttle it dies almost completely. Scary shit when you are in a crouch and then the power stops.
Can hear it pop, burble and fart out the exhaust but it will then come back on and will take about 90% throttle and will scream down the rest of the strip. Give it 100% throttle you can feel the power go soft.
It does 13.2 second quarters consistently with this condition but way way too dangerous to continue in the hope it will clear itself like it was just some shit in the fuel. Should be able to pull 11.5's so we are way off the mark.

Also if you free rev it to around 5,000rpm - 6,500rpm you can hear the exhaust crackle like a misfire.

What I have tried...
New plugs
Different coils
Different CDI
checked and adjusted TPS
Cleaned out carbs again including all jets and emlusion tubes
checked float levels all 13mm
Set pilots to exactly 3 turns out before reinstalling
checked carb sync was all good
Checked battery voltage and charging voltage within spec

What I havent tried yet...

Checking TPS for continuity of signal / resistance (what would happen if the TPS loses signal at that critical position?)
burning it

Ideas anyone?

Best regards,
Rusty (due to crying on myself)

From what I have read, CV carbs rely on a vacuum to operate the needle. CV carbs are a great thing for OEM from an emissions standpoint but not so great for outright performance. Flatslides are say the equivalent to a nice pair of IDA Webbers or sidedraft Dellortos - those of us who remember the 80's and 90's car scene before EFI will know what i'm talking about.

Things I have found...

K6 bandit 1200 didn't show any signs of flatspots when I fitted jets using educated guesses and a K&N air filter with the magical 1.5" hole

K4 bandit 1200 had a shocking flatspot using a K&N and very similar mods to the K6 but was fixed outright simply by fitting a "standard" type air filter

K5 bandit 1200 that was absolutely out-of-the-box showroom stock standard in every way ran as Mr Suzuki intended but as soon as you fit just a K&N air filter - it ran like a bag of shit.

Note that the Mikuni model number is different between K1 through to K5 and the K6.

Something in the design perhaps of the K6 carb that make it accept the K&N flow characteristics over the previous model?
Another note that the K6 was the only bandit to use that particular model Mikuni.


My questions...

Can anyone who had fitted a Holeshot stage 2 kit to their 2001-2006 bandit give a brief of how the bike runs now after fitting?

 DW's stage 1 kit says not to use a K&N (i'm guessing because of what I found) but his stage 2 uses one.  How does DW eliminate the flatspot in the stage 2?

Bueller......
Bueller......




Bueller......

I really don't know how to interpret that last picture, Bosco.

Or the 2 before it ?

Ironman wrote:I really don't know how to interpret that last picture, Bosco.

I reckon he must have been pissed last night. That post should have gone into "funny stuff that's no joke"

No, there's a Buell..er.

And a trackday which leads to over sized appendage, similar effect to a loud slip-on.

Maybe he missed the reference to Ferris Bueller's Day Off.

Must have a low slung crutch in those leathers ................

no I bet its just folded or even rolled up. just dont forget to unfurl it before "turning the hose on".
ever seen an out of control fire hose?

UPDATE...
Bike had a huge flatspot when using a K&N. Fixed without having to revert back to a standard type air filter.
No matter what pilots, mains or shims under the stock needles are used, it's the needle profile and slide springs spec that fixed it.

So will verify the difference and get some numbers next drag meet and the weather isn't either freaking hot or wet... or both for that matter.

There's some good airbox science reading here CLICK

some interesting reading indeed. thanks!

The latest Classic Motorcycle Mechanics has an article on a stage 3 kit . He also had problems with the fitment of a K@ N filter with the kit .
My 1200 came with a K@n and runs fine so I think its whats WITH the K@N that gives the problem .