Hello, I have a 08 ZX14 with about roughly 40,000 miles on it that is bucking/bogging at low rpms. When I start the bike it runs totally fine until it warms up to the middle line on the temperature gauge. It then will start a rough and choppy idle. When I am riding it I experience the shuttering/bucking very bad in the low rpms and if I accelerate it disappears and runs perfect. This issue only shows when the bike warms up.

Some additional details from the past that could help point you in the right direction of the issue. In the past the bike had a crack in the overflow pipe inside the gas tank and water would get in the tank. This is around the time the bike stopped running right. I changed out the whole gas tank with a new one and put in a new fuel pump. (I thought maybe since the fuel pump had seen a good amount of water and abuse that it might not have been running right. My only guess is that when the bike warms up it might be causing pressure or something in the tank causing the bike to run weird) This did not solve the issue. Bike started up and as soon as it warmed up it started same symptoms.

I have ran a bunch of injector cleaner through the tanks and nothing seems to help. (Thought with all the water in the tank in the past that maybe the injectors are all gummed up.

One more idea that I had was when I bought the bike it had a power commander hooked up and I removed that a while ago. I have had the bike for about 4 years so I doubt this would cause an issue now. I have seen some similar posts with similar symptoms and they say it just needed the correct maps programmed again.

Any help would be appreciated.
Attached is a short video of the idle

https://www.youtube.com/shorts/QDc78GdKyoI

... it had a power commander hooked up and I removed that a while ago.

So you had this issue before removing the pc? Is this still hooked up in any way, or completely removed?

I have had the bike for about 4 years so I doubt this would cause an issue now.

When you removed and replaced the tank and pump, the issue started then? Or was this found when chasing the problem?

I've heard a stumble at around 3k rpm range. It took an ECU to clear it up.

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Thank you for you response. Sorry if my post is a bit disorganized.

To answer your questions:

So you had this issue before removing the pc? Is this still hooked up in any way, or completely removed?

To give you a time frame I bought the bike 5 years ago. In the first year I pulled out the old pc and all the wires because it was not hooked up correctly and there were wires everywhere. The bike ran perfect without it for 4 years. Randomly in the last year it started running really choppy and that is when I figured out that there was a leak in the overflow pipe inside the gas tank and water had been getting into the tank. I rode the bike for a few months when it wasn't raining and the bike still had the same symptoms. (Even after running sea foam, probably 20 + tanks of premium gas) That is when I bought a new gas tank and put that in with the old fuel pump. Bike still ran terrible. Most recently, I bought the fuel pump and it still starts chopping right when it warms up.

When you removed and replaced the tank and pump, the issue started then? Or was this found when chasing the problem?

The issue started before I touched the tank or fuel pump. I just knew water was leaking in through the old tank and after a few months I pulled the trigger and bought a new gas tank.

I've heard a stumble at around 3k rpm range. It took an ECU to clear it up.

In regards to the ECU, if I changed this out what would be the best direction to go? Find a used ECU and put it on or buy a Schnitz ECU Reflash. Do you think this would just remove that stumble you heard or possibly fix the whole issue?

Thank you for getting back to me so quick.

Someone sent me that ECU I mentioned so I could feel that digital blip at that certain rpm. It was more like at cruising speed and it would come and go if you matched that rpm hit, which was quite annoying, the coming and going of it. Any resemblance to this driveability symptom?

Can't say for sure throwing an ECU at it will do it. A flash won't help I'm guessing. This was one variable to a sputter type scenario. I'd more have to ride it to see exactly how it feels.

Your dash showed no codes while idling, so you can't point to a sensor out of range or a wire dropped from either end. I had an '08 and an '06. I'm wondering if his was the same year or older? It was a plug and play between years.

When you say it cleans up after getting out of this bucking/bog window, it seems to eliminate any kind of fuel or ignition components.

Fuel pump: Starts the bike, shows fuel delivery at higher rpm... not this.
Spark plug and sparkstick: If it was a wire [resistance change] it would do it in any range. If it was a spark plug it would buck and bog at the higher rpm range... neither these.
Injectors: Starts, idles, delivers up top... or this.
ECU: Your guess is as good as mine. No codes, WATTS left?

Exhaust: That would throw a question as to needing it dyno'd to watch the AFR change. A bucking at a sustained speed would be loss of gas? The bogging would be a loss of power or less gas? Again, I am just guessing without a ride.

Carbs were a more simple tune to shuffle fuel around. FI needs to override the OEM map for this bog tune is the guess to a pipe change? Where you can cork the end off with a hose clamp and the right can of said peas, corn, tomato sauce size can over the end of the pipe. A couple of can opener hits at around say half the can, pop the lid back, and adjust it closed or opened more at this bogging window and if it cleared it up, it's not the ECU.

Have you changed the spark plugs every 7,600 miles per owner's manual? This would be a good time to see how the plugs read. Once out, new goes back in. Stick with OEM.

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It was more like at cruising speed and it would come and go if you matched that rpm hit, which was quite annoying, the coming and going of it. Any resemblance to this drivability symptom?

This sounds very similar to what I am experiencing. When I am driving at low rpm's or when I start off from a stop, it will buck really hard in the low end. As soon as I open it up and get above 5000rmps the bike runs perfect. This makes me lean towards

A bucking at a sustained speed would be loss of gas?

. Very weird that on the top end it is being fed the right amount of gas and on the bottom end maybe the pump is pushing in too much fuel causing it to stutter until I speed up? Just a thought.

Exhaust: That would throw a question as to needing it dyno'd to watch the AFR change.

I do have the voodoo exhaust on the bike, but the weird thing is it ran perfectly fine in the past with these on. Only started running terrible when the water got in the gas.

Where you can cork the end off with a hose clamp and the right can of said peas, corn, tomato sauce size can over the end of the pipe. A couple of can opener hits at around say half the can, pop the lid back, and adjust it closed or opened more at this bogging window and if it cleared it up, it's not the ECU.

Is there a video of someone doing this? If not, do you mind explaining further. Would love to try this.

I have not changed out the plugs recently, It probably wouldn't hurt to get them done. ALthought, I don't think this is the issue because at higher rpms the bike runs flawless.

Thank you

Years ago I owned a Hayabusa with a stage2 turbo. To keep from melting pistons it had a water bottle kit that would spray a small amount of water into the cylinders. I had a wire connection short out causing the water kit to spray a crap load of water into the cylinders. Lol the white smoke that came out my dump pipe had me thinking the motor crapped the bed. Anywho my point being once I figured out what the issue was and fixed it. The bike sputtered in the lower rpms consistently but cleared up and ran perfect higher up. Finally changed the plugs and no more sputtering. Not sure why but once those plugs took the bath they wouldn't fire properly at lower rpms....

All the water will do is steam clean the carbon from the cylinder chamber. Piston dome to head. Like blowing a head gasket. Parts look like it came out of the box.

The exhaust was just a variable. That trick is more to keep the fresh unspent to be pushed back in on reversion. But since you pointed out that it never did it with the exhaust change, that cancels that variable. Which is more a pre fire, meaning, it's calc'd with the correct fuel demand.

With Bk's spark plug input about a plug swap cleaned it up, the cheapest [test] and do one thing at a time. I'd go for a set of iridium plugs [OEM] and test ride.

The trick with the removal of the spark stick is connector off, then twist the stick and pull up. Look at the cast-in lineup bump on the cam cover. Take note before removing stick.

* Last updated by: Hub on 5/3/2023 @ 9:44 PM *

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When I am driving at low rpm's or when I start off from a stop, it will buck really hard in the low end.

That start from a stop sounds more like a sprocket change. I believe stock is 41 tooth at the rear. It's stamped on the sprocket. Check that first.

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Finally changed the plugs and no more sputtering. Not sure why but once those plugs took the bath they wouldn't fire properly at lower rpms....

That sounds very similar to what I am experiencing. I will tackle the plugs and see if that makes a difference. Appreciate your response.

With Bk's spark plug input about a plug swap cleaned it up, the cheapest [test] and do one thing at a time. I'd go for a set of iridium plugs [OEM] and test ride.

Thank you for your help. I will give that a shot and let you know the results.

Yes please post results either way. Nothing worse than unanswered questions....

Hello, Hub and BK1400R. Quick and happy update for you both. Changed out all the plugs and two of the old ones had a ton of white residue on the bottoms of them. Slapped the new ones in there and it started right up and the bike runs perfect. I rode last week with 80 degree weather and the bike still runs perfect with the high temps.

I appreciate all your help throughout this process.

Thank you and safe riding!