B1200 Mk2 HUGE flatspot

[ironman]

Hello Everyone,

New member from Australia. Been riding Bandits for 6 years and have owned 9 so far and still counting.

I do track days and drag racing, done engine swaps, suspension, tear downs and rebuilds.

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 and seems to have a uniform linear resistance reading
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

Fuel tap flows easily when it is supposed to

 

 

Any suggestions are warmly accepted.

 

Cheers and thanks!

 

 

[Captain Chaos]

Hi and welcome.

Aren't those main jets awfully small?

[Gixer1460]

Not for a Bandit in that state of tune. Personally i'd throw a DJ or Factory jet kit at it - mid range tuning is a PITA generally!

[ironman]

Would worn needle jets cause this? I hear that the needle wears these oval over time. 

[fatblokeonbandit]

if it was me id tape the hole up and try that.. ive had a couple of 1200's mainly mark 1 with the different carbs than yours, but with just a race can and k and n filter I have found that 10% increase in main jet size usually works well

 

or your emulsion tubes are oval

[ironman]

where do you buy net needle jets?

[fatblokeonbandit]

In Australia not a clue, there are some members over there,  put a question in the general section and see if any of them know of good cheap supplies over there

[ironman]

ok i think i have found someone to supply.

As a side tuning note, shortening the slide springs by 20mm will that allow the slide to rise a touch earlier and come onto the needle sooner?

[fatblokeonbandit]

Dunno matey I hate messing with carbs, spent tooo many hours changing jets and settings in the past, if its not something simple  I go straight to a dyno and have them set up nowadays...soo much easier and its right first time

[Captain Chaos]

I had a similar problem on my B12 engined EFE. Turned out the slides were lifting too fast.

The two holes in the slides were 4mm each, I installed some slides with smaller holes and it was OK.

[Quist]

Try stock springs. But use thinner needles like Dynojet or Factory Pro. 

Or the best answer, dyno  Within minutes you know where too look and adjust to solve this problem. 

Build my 750 with complete different carb setup after bought it stock. Within 1,5 hour we got good numbers on the dyno and 11.5 on the quarter easily.

 

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

[dupersunc]

Diaphragms on the carbs are all good?

[Gixerjonah]

That fat bloke on a bandit knows what hes on about !! Go to a reputable dyno, its the quickest & best way.

[Foz]

2" hole mod on a mk1 1200 and I ran 127.5 main jets so I'd say the 110 mains are to small. I ran 110 mains just to richened it up a bit when it just had a k&n panel filter and race can 

[ironman]

Update...

Fitted a new "Hiflo Filtro" OEM type replacement filter.

Like night and day - it works!

Best run for the night was 11.9 @ 189km/h (approx) with my 120kg bloated body as a passenger

Pulled the plugs and inspected after 40km of drag racing they look too clean to me. No discolouration at all.

 

Ive ordered some 115 mains to try on a track day in 3 days. Ill swap the mains out and change nothing else and see how it goes.

During a break ill refit the K&N and see what happens. Hopefully it doesn't die in the arse and pop me up on top of the fuel tank like it did when drag racing.

 

Question is why does the K&N cause this flat spot and how would I correct it?

How much of an overlap if any will main jets have over the needle and pilots over the needle?

 

Reason I ask is I have a generation 3 bandit 1200 (last of the oil cooled before the new EFI water cooled version engine came out) and it pulls like a  schoolboy who just discovered porn. It has a K&N with 112.5 mains, stock sized pilots but screws nearly 4 turns out.

 

Any wisdom would be very much appreciated.

cheers everyone!

Edited November 23, 2016 by ironman
stuffed up the measurement

[ironman]

Anyone?

[gsx]

Sounds like mains are too small , try 127 as suggested above .

I run dual pods with factory pro gsxr 11 kit ,cheap as chips and same emulsion tube part number , 150 mains .

Think your strangling it coming onto the mains which are too small

[ironman]

Thanks gsx!

Im out of 127 mains. The 115's are out of stock so I have a set of 117.5s on their way hopefully to reach me today, to be fitted tonight to track it tomorrow.

 ill try the "hi flo filtro"air filter first to gauge how its going then Ill pop in the K&N ...Ill post up how it goes.

 

[gsx]

No expert but with the large hole in the air box it may end up between the two .

As fat bloke said  earlier , with the jetting you have it may be worth blocking up the air box hole and trying that

[fish91]

As mentioned previously try bigger mains. I've pissed about for hours with my mk2 B12 and 110 arn't big enough for a stock filter with the hole mod, let alone a k&n filter. 

Setups in mine currently is 117.5mains, bottom needle clip, stock filter with hole mod. I've also tried 127.5mains, bottom clip, k&n w/hole mod.

[ironman]

Hi fish91

And how do those two settings run?

Ive just finished fitting the 117.5s.

 

[fish91]

5 minutes ago, ironman said:

Hi fish91

And how do those two settings run?

Ive just finished fitting the 117.5s.

Pretty much spot on, nothing in the way of flat spots and pulls well through the whole rev range.

[ironman]

Tried the 117.5s at track day with standard type air filter with airbox mod

Pulls well enough through the midrange but topps out around the 8.5K mark.

Enough power to overpower the standard suspension.

Here's a pic of plugs 3 and 4. Thats after 40km of drag racing and 80+ km of trackday.

[Oldskool]

On 10/17/2016 at 8:28 PM, ironman said:

where do you buy net needle jets?

Go to the dynojet web site and check jet sizes, then order from Show and Go in Adelaide.

[Antman]

Gyday

Where are you from?  I'm in Syd.

Mick Hone Motorcycles in Melbourne should have the parts your after.

How was it running prior to opening up the box and K&N filter?