Recently picked up a 2003 cbr600f4i. From the moment I got it, it ran good except in the lower rpms where it would have trouble getting to speed below about 4-5k rpms, past that point it would fly. It was also idling kind of low when warmed up at about 800-1k.
It was riding fine like this, however, until I went for a ride a few days ago and midway through she started to bog down and wouldn't accelerate past about 13mph. It still starts up every time and has a consistent idle, but lags when I rev it in gear or neutral and wants to bog down in gear. It's extremely sluggish going the low speeds that it's able to do.
Before this ride, I filled up earlier in the day and decided to adjust the idle screw to get it to idle higher.

It's currently sitting in my driveway waiting on a new fuel pressure regulator and spark plugs. Thinking either of those could be the issue but any other insight is appreciated. It's also straight piped, but I wouldn't think that that would cause this big of an issue. Regardless, I ordered a muffler for it as well because it's way too loud.

 

Hey, I know this thread is old but OP did you ever figure out the issue? I’m running into something similar and it’s really been a pain in my ***

 

Don't hold your breath for a reply.
Last Activity: Oct 27, 2022 10:34 AM
Hasn't been seen since 39 hours after his first and only post.

 

Hey, have you found where the problem is? I have really similar issue
Here is my thread https://cbrforum.com/forum/general-t...ow-rpm-165115/

What i found for now is my 4th coil not working. When i unplug 4th coil while engine is running there is 0 diffrence in sound or engine performance at iddle. I have not change coils positions yet but ill try do it soon