Q. My Kawasaki ZX-7R P4 has an intermittent running problem that has me stumped. On cold mornings it will start fine, run fine for about five or 10 minutes then sometimes it will stutter and feel like it’s lost a cylinder or two.
But it only does this below about 5000rpm and with only a little bit of throttle; if I open her up it seems to pull through it. Then occasionally, but very rarely, it will just clear itself and run fine.
I’ve had the coils and HT leads checked and they're fine.
R Taylor, email
A. Those are all the symptoms of carb icing. What happens is that cold and damp air being drawn through the carbs at speed forms little ice crystals that block the jets, interrupting the fuel flow to the cylinders.
Check that any carb heating kit fitted is working properly. The filters might need replacing, and get a fuel additive like Silkolene Pro-FST.