Hiya members, hope everyone is doing well! I need to call upon your help once again.

Bike
I have a '98 CBR600F3 which is fitted with a K&N airfilter and Sebring slip-on. It's been like that since I got it and it has always ran beautifully.

Problem
The other day I brought it into the shop for a new front tire and decided to let them change out the sparkplugs since I have never done that before and I thought they were a pain to reach. Yesterday I took it out for a long ride and noticed a problem. When driving in a lower-RPM range ( 0 - 4500 RPM ) and snapping the throttle to the full-open position the bike will stutter and hesitate a lot. Eventually it will go and launch to redline without any problems. When i'm gradually rolling on the throttle there's no problem. The problems seems to be most noticeable in 2nd and 3d gear.

What I've checked
Now, I know the shop had removed the airbox and coils to reach the sparkplugs. So I decided to remove the airbox myself to check if there maybe was false-air leaks. I didn't found any. I have limited knowledge of coils and am not sure how I can check if they are not functioning properly. Also I have limited knowledge of fuel-mixtures but I'm a quick learner. I don't think this is a jetting-issue. The bike has always ran fine with this setup and only the sparkplugs were changed. When I start Googling myself I read advice from fuel-filter to jetting problems etc. I'm a bit lost where I should start.

So my questions to you:

• Can new spark-plugs cause my problems?
• Do you guys have some advice for to for stuff I can check myself?

And oh, p.s. I know I should bring it back in to the shop and I probably will do so but I can do that later next week and figured it might be a nice time for me to learn something myself. Thanks !

 

Hi Nils , maybe just check all air hoses have been put back in place, and they haven't kinked any fuel lines in the process of removing the tank

 

Hi mate! Thanks for your advice, I really appreciate it.

I've just checked the air hoses and fuel lines and all seems in order.

I have a feeling that this cannot be a jetting issue since the bike ran perfectly fine before the spark-plug change and the carbs haven't been taken off. Do you agree with that? I've ordered a new fuel-filter since it's rather cheap and I haven't swapped that before. But by reading my manual and some online topics there's a thousand things that could be wrong. I've never been the type to start swapping random parts so I'm kinda unsure as to how to proceed from here and start eliminating possible causes.

The things that I came up with this far:

• Air leaks in air box (checked)
• Air hoses not put back in the right place (checked)
• Fuel line kinked (checked)
• Spark plug gap incorrect (would this explain why the hesitation only occurs under full-throttle at low rpm?)
• Fuel pump defect (not sure if this is possible since it does perform well when I gradually open the throttle)
• Broken coils (not sure if this is possible but I know they took them off the bike

Any tips would be really appreciated!

 

Do you know what they swapped the spark plugs to , where they as per workshop manual,

 

They used the plugs as described in my workshop manual. I took the DAI system apart and put it back together and now the issue seems noticeable less. Perhaps it was caused by misplaces tubes after all or perhaps it's that valve that opens above a certain speed (I don't know the name). I'm not sure if i'm able to check the operation of that valve somehow but for now the hesitation is within acceptable margins!

Thanks for you advice buddy, really appreciated !

 

Its the Air Solenoid, there is an Electrical connector on it that is coupled with the Speedometer ,and at between 12 and 20mph it switches for the smaller air pipes to the large intake, if the solenoid is working properly, some riders bypass the air system but I would say stick with it

 

It is possible that they didn't get the plugs seated all the way. There should be a decided "click" when they seat properly. One thing to look at is the boot seals at the top of the plug holes. If properly installed the seals should not have a gap of any sort around the plug hole.
FWIW it isn't required to remove all that to change your plugs. Removing the side fairings you can get at the plugs that way. I find it much easier that way. But that's just me. I guess it's a pick your poison type of thing.
There should be a diagram of your air house routing on the top of your airbox. If not there's one on pages 1-26 through 1-28 in the manual.

 

It’s pretty simple to remove the air solenoid, if you google it there are plenty of diagrams online, IMO it’s completely unnecessary all the race bikes have it removed.