I have a '03 ZX7R and it's started to run rough at low RPMs. Kinda sounds like it's running on 3 cylinders but I know they're all firing. Basically it runs like crap up until I get it out and run it at highway speeds. Feels like it accelerates and seems like it runs smooth up until I slow down. Stopping and taking off again it almost wants to die but on the open road it feels normal.
New plugs and just cleaned the carbs.
Any help would be appreciated!
Hi and Welcome! I will hint that there are more appropriate forums for this question as
this forum supports the FZ 6 from 04 - 09, but a bike is a bike and we'd be happy help!
Besides; Most of us here have no carbs so keep that in mind!
IME - it sounds like you have a fuel leak.
That is, unmetered fuel is making its way through and into either the idle circuit or the main circuit and flooding specific cylinder(s) at low RPM. As the RPM comes up, there is more air to 'match' the fuel leak and it cleans out and begins running on all 4 cylinders.
You didn't mention why the carbs were apart
but if rust or sediment was involved, it often times hangs up a needle allowing that unwanted (think excess) fuel into the cylinder(s).
To figure out which carb is the problem you can do one of two things:
- Pull the plugs and inspect for wet plugs and/or those smelling gas. Then look to the wet plugs carb as the source of an internal fuel leak!
OR
- If you let it idle long enough it will misfire from running too rich (too much fuel for the idle speed and air being mixed with it).
Use a squirt bottle full of water and mist each header pipe 6" from the head. The pipe(s) that flash off as steam first have a reasonable "Air Fuel Ratio" (Carb is probably OK).
Those that hold moisture longer are too rich! The carbs associated with the wet pipes need to be inspected again and determine how unmetered fuel is getting to them.
Fuel systems need to be VERY clean! Rust in the tank will cause the issue you mention here. Insure you have a good fuel filter and a rust free tank!
If the carbs were apart for another reason (tuning etc), please list some details about why you took it apart and what you found along the way!
Good Luck!
