B1200 MASSIVE mid throttle flat spot - help?

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)

Well Rusty ,the first thing id try is putting a standard air filter back in .I put a K@n in my 1250 and it didn't like it .I know people fit the to a 1250 and have no trouble .
You could ride up to my place and we could swap a few parts around till we find the problem ( I own a 1200 now)
Today I pulled apart my 600 Bandit carbs looking for a rev problem . I found a o-ring and washer on a pilot jet the wrong way round .
It sounds like an air ,fuel ,problem to me.
I just re read your message .
Float height you set at 13 mm ,upside down to top of floats .
Isnt the float height supposed to be 17mm _+
Runs fine ,runs out of fuel, carbs fill away you go again ?????????
No ,sorry your right 13mm ,I googled it .
I just did mine today ,600 bandit . I  think I set the 1200 the same 17mm thinking that it would be the same .
I still think it might be worth a try ,sounds like its running out of fuel .

These old girls have vacuum operated petcocks right?
That's worth checking because it sounds like it's a fuel supply issue causing a lean pop in the exhaust system.

Main jets might not be correctly sized to match the other mods/setup. Just speculation on my part but I had an old 750 that did that and it was the main jets.

I realised during an episode of "Suits" last night I have it wrong .
13 mm means you have MORE fuel not less .
We did have a problem once on the Bonnie where the fuel line would kink with the last 5mm of the tank being fitted .Bike would run fine until you wanted more power .

I checked it against what the manual says 13mm from gasket surface to the highest point of the float just as the valve seats but not compressing the spring. It took me a bit of squinting, head scratching and a few utterances of,"how the fknell do you measure that?" before the lightbulb switched on.
All carbs measured up at 13mm i didn't have to adjust them. Emptied most of a full can of caby cleaner into these carbs in attempts to clean any shit out.
Ive checked for flow at the fuel tap on prime it pours out. I might check again on the other settings.
Ive pulled the spark plugs all are identical looking sooty base ring electrodes are whistle clean.

Can someone with a 1200 try this for me?
Disconnect the tps and take it for a bit of a thrash and tell me what difference it made?
Just a hunch but i'm thinking that my TPS may have a inconsistent resistance signal to the CDI maybe causing ignition to become less than ideal.

I just can't think of what else I can try.

Send me a pic of these TPS and directions to disconnect - I've got an old 2002 1200S so happy to give it a crack (and go for a thrash)and give feedback if it helps.
Wont be able to do it till later this week though.

Thanks Truck. The TPS is on the RH side of the carburetors - the black plastic sensor with a connector. Simply pull up the plastic cover and disconnect. Go for a blast and see if it rides any different.

I did a bit more testing and it misfires from anywhere 3000 - 5000 rpm but it really seems dependent on throttle position.
Ive checked for uniformity of resistance from the TPS and all seems fairly linear and only having a digital multi meter it is a bit more difficult than a good analogue one.

I've never come across a problem using K&N air filters in the past. Every bandit I've owned (9 so far) has been adorned with one of these.
Things to try...
I did read somewhere that Dale Walker advised a customer who was having tuning difficulties with his jet kit to shorten or something the carburetor breather tubes. 
Swap air filter to a stock one and try again
The misfiring seems to be around 1/4 to 1/2 throttle - needle height?? Maybe lean it a bit? (on richest setting ATM)
I've checked the pilots I installed 17.5's up from the standard 15's. Same number of holes etc as I heard that there were some with no holes and some with lots and that created more problems.
try another set of stock carburetors and one and a time adjust things.
or just buy a DW stage 2 kit and be done with it.

Just my 10cents worth.

I agree that it would be just about impossible to test the TPS with a digital multimeter and it would be fairly challenging to find one these days.
What may be easier to source is a digital storage oscilloscope. They are available for under $100 either with a built in LCD screen or ones that connect to a laptop via the USB port.
Easily sourced from Banggood or many other suppliers in China.
Quite a useful addition to your toolkit particularly as bikes are getting more electronically sophisticated these days.
Setting the oscilloscope on a slow timebase it should be easy to see any glitches as you rotate the TPS through its range.

Someone else mentioned fuel delivery.
I wonder if replacing the existing vacuum operated tap with a manual one possibly with a larger diameter hose as well would rule out fuel starvation.
This would at least completely rule out one possibility and allow you to move on to another issue.

If the fuel tap is like my old 1200 it has 3 positions, Pri Res and Normal AFAIK Pri (for prime) is the manual on position so if it flows plenty of fuel in that position you can forget vacuum if the problem is the same in Pri.

Ironman wrote:Thanks Truck. The TPS is on the RH side of the carburetors - the black plastic sensor with a connector. Simply pull up the plastic cover and disconnect. Go for a blast and see if it rides any different.

Ironman, 
I disconnected the TPS at work, no difference it idled the same, revved the same, sounded the same. 
I give it a bit coming home and the old tank pulled all the way through to 180 twice as per normal with no noticeable backfiring or missing. 
*Note my bike has not been tuned in a very long time so maybe it is missing and I have got used to it over time.

Good Luck!

Thanks Guys,
Well I checked the fuel tap. Pri = fuel pours out; Res and ON = nothing but add a little bit of vac and it too pours out.

I'm thinking that maybe with reduced free height slide springs (20mm) shorter and the needles on the bottom clip it may well be too rich?
I also have 17.5 pilot jets in @ 3 turn out from seated (standard pilots are 15's @ 3 - 3.5 turns out)

The airbox has the standard snorkle in but an additional 1.5" hole in the top with a radius to smooth the airflow.

Too rich?
PLugs base ring is sooty but clean electrodes and inner insulator.

Should have just bought dales kit.

Its a real bugger because the bike is a repairable write off I bought to do drag racing and track days I can't just take it for a run around the block. I have to trailer it and hour away to willowbank and pay $45 to run it on the strip and when it isn't enjoyable nor safe to let it off the chain, its real frustrating.

My lads 1200 used to bog down like when he fitted a K&n filter (with exhaust already previously done) his choices were put the old orig filter back , or change the jetting .( With the orig. filter back in , the flat spot went away) Maybe a race tune specialist could suggest the best carby set up .

(lack of) Fuel problem. Check the fuel line is not crimped when replacing the tank. I'd look at float and move the level 1mm at a time to eliminate it.

CV carbs need tuning from the top down, that is get it running best at WOT even if it coughs and farts down low by trying 3 or 4 different main sizes 142.5-150 or there abouts. Then mid range, then just off idle.

Get some pod filters to make removing the carbies easier as you may have to do it 10 or more times, and get them first to negate having to re tune the bike for the pods.

CV Carbies

more mikuni....

getting the cables on and off have got to be the hardest thing to do when you have 10 thumbs

I'm going to try changing the air filter from the K&N to the standard, See what happens.
DW says not to use a K&N on a stage 1 (which effectively is what I have here) so I reckon he knows what he's doing.

I set up my old 1200 to run a K&N and you are a good 10 points off on main jet size. Try 120s.

Also take the bike out and sit it in the bad zone then quickly hit the kill switch and pull the clutch in. Then stop and pull a plug out. That will tell you whats up.

Ill pick up a new standard air filter tomorrow. 
Test and tune is tomorrow PM so ill know whether to burn it or not.

Anyway I'm in contact with Holeshot Performance to get a hold of a stage II kit and advancer - that'll get it going!

We have a result!

Gus was right. I've never encountered a problem in the past with a K&N but after cleaning out the carburetors and checking EVERYTHING it still hadn't cleared up the deepest hole in the power curve.
I refitted the air filter gaskets (lucky I kept those) and popped a brand new standard type air filter in.

I was apprehensive on going out the the drag strip as there was rain forecast and the sky was looking dark with heavy cloud.
I checked the rain radar and the social media page of the track. It updated just as i checked it -"its fine and the test n tune is on for tonight" it said.
OK so hooked up the trailer and dragged it all out there.
I must say on the way there it looked as though I was going to be pissed on from a great height but it held off.

Long story short... signed on; geared up; waited in staging lanes; waited; waited; waited.............. waited................ waited...
my turn WOO HOO!
Staged and got a green light - my take off was hesitant because I didn't want to be riding on the fuel tank again due to a gaping chasm in the power curve.
Well no flat spot. Right O I opened up the taps and let her off the chain as fast as I could. 12.2 sec at 189.8 km/h.
Considering a very sedate start (as you can see in the video) I was happy the flat spot was filled in.

Right lets do that again. Back around and wait again......... and waited...... waited....... waited.................................................................... is that rain?
one spot, two spots light shower. OK hope that's all there is. I arrived there at 4:15 got 1 run in at 5:30 and they cancelled the night at 6pm.
Well the sky was like that kid you see at the park, busting for a leak and dancing around the place and suddenly can't hold on anymore.

I got only 1 run in before they canned the day with no offer of a discounted admission fee next time or any sort of refund.
Am I expecting too much?

Anyhow I did get 1 run in and the flatspot is gone but what I have learnt is that if the sky looks like it's going to rain, the BoM says it's going to rain, the guys on TV at the GC600 say it's probably going to rain but the race track dudes say its fine and the event is still on...... stay home and watch the racing.

Nice work Ironman and all who helped, Also answered a lot of questions I no longer need to ask ! After completely stuffing up my perfectly good 05 1200 after recent fitting jet kit and slicing my airbox lid clean off @ 25mm from flange with KN filter blah blah

Gunna put all stock gear back in and try super glueing my bloody airbox back together for now.

Great info guys

Cheers

Got out to Willowbank yesterday for some testing.
Managed to get at least 10 runs in. With the flatspot issue resolved it was down to seeing what sort of times I could get.
First of all it was bloody hot. 37deg c during the day and wearing a leather jacket, back protector, leather gloves, full face helmet, kevlar jeans and boots made it feel like an absolute oven.
The oil cooled Bandit got pretty hot too. After a few runs I went back to the pits to cool off a bit. I grabbed my temp gun and found it had a barrel temp of 135deg C after a bit of a heat soak period. Oil cooler was at 90deg c.
Best run of the afternoon was an 11.996 @ 186.20km/h ambient temp was 32deg.  Worst was 12.5 when i missed a shift and found the rev limiter. I got my arse smacked by a fleet of gixxers, 'blades and a 'busa but by only between 0.4 and 1 second.
I pulled out the plugs today and found the insulators were whistle clean with a hint of carbon on the base ring. I reckon I could try one size bigger on the main jet and see how that goes but all in all after 20km of flat out, nuts pinned to the wall, taps opened wide in the tuck position rookie drag racing it was running okay and I'm pretty happy with it.

This result from a heavy bike with a 100+kg throttle/clutch operator I thought was good when the guys (and girl) riding the other bikes were test pilot sized.

Must say also I'm a bit over the drag racing now. Yep its a rush to give it everything its got and do speeds where you would be standing tall before the man if caught out on the street but after 10 plus runs and my consistency was good, i tried different shift points and clutch slipping and just couldn't squeeze any more from it. To go faster / quicker requires more money, more testing, more trips out to the strip and doing all that by yourself gets a touch boring. Ill try some track days next.

(oh yeah i stalled it just off the line too by giving too much clutch     - better than the poor guy last time who had more revs than i did and flipped his brand new bike....didn't end well - made for a great sequence of photos on the sports photographers website!) 

Anyways, to those still fiddling with the 1200's - cheers!

This is my 2004 GS1200SS at the 2009 Winter Nats....I got as far as the semi finals and was running around the 11.6 sec mark.
I was the NZ Mod Bike Champion for 3 years in a row on the old GS1200SS.
Plus I got to race at Alice Springs and Darwin as we had come over from NZ for the Trans Tasman Drag bike Challenge.

Thanks
Richard

Ironman, 

As you've got the problem pretty much sorted, this post is really only of academic interest.

Those are CV type carburettors, right?  Diaphragm actuated.  

It is my understanding that removing stock airboxes usually does the tune no good, as the partial vacuum created by the airbox is what actually provides the actuation of the needles, raising them, providing more fuel.  Is this right?  

Replacing the airbox with free flowing pods would reduce this, so would result in fuel starvation.  

I am looking to be sorted out if I have this all wrong.  

Comments please, from anyone.  

If this can be discussed, maybe we can save others chasing faults which either don't exist or are of peoples' own making.  

... and so I can make some rational decisions about how to go about fixing an issue on another bike I own (not the Bandit.  Mines a 2007 fuel injected GSF1250S)

I have a 86 SRX6 which has a conventional and a CV.  It's never run right.  It came with pods.  An effort was made to tune it by a mechanic with a Dynojet kit. that was not helpful.  I've put an airbox into it - that made it worse.  I'm starting to think I'll just have to bite the bullet and go for a pair of conventional flat or round slide carbies.  

I'm just trying to clear up my understanding of the difference between CV and conventional carbies.  It has occurred to me that I might try a sock on the CV carby - over the pod, to restrict air flow to it. That might be the last thing I try before I just bite the bullet and get some other carbies, or a Y shaped manifold and go single.

@ewok1958 might be able to help out here too as he mucked about with the carbs on his xs

Hmm, not sure I can help. I got the XS850 running with the pods in place because I got sick of trying to remove the carbs with the airbox in. And I had to pull the carbs off quite a few times. And the XS850 has Hitachi carbs - the only other bike I know with those carbs is its sister, the XS750. I don't feel I'm getting any fuel starvation with the pods though.