Hey guys, not sure how many of you know much about cbr's.....but I've a friend with a 99 F4 that has some strange issues.

The bike has been sitting for a while and just got it back on the road. It had an occasional misfire under load at mid-range rpms, and it progressively got worse to the point it would miss at idle from time to time. We replaced the plugs in it and it ran fine for two days, however the problem is starting to reoccur.

I'm beginning to question whether it may be a cam/crank sensor or coil failing. The coils ohm out perfectly(warm), however thats never a definite answer.

If you've any input, I'd surely appreciate it!

Thanx!

 

sell it and buy a gsxr. Its probably the coil. but its hard to tell, take it to a bike shop and have someone look at it instead of throwing parts at it.

 

buy a GIXXER..

 

Was there old gas sitting in the tank during storage? Make sure there's fresh fuel - could be clogged jets in the carbs as well...

 

fresh fuel, I think he even threw in some 112 just for ****s and giggles...

 

i dont think that model is fuel injected! the jets in the carb are most likely cloged

 

depending on how long it sat (if it was 3-4 months) and he didn't drain the float bowls on the carbs, the idle jets (fixed jets) and air passages are probably clogged. soak em in some carb&choke cleaner and get a jet cleaning tool (or you can use some lengths of stiff stranded wire, like zip cord or speaker wire strands) the jets are tiny... just ream em out w/cleaner and wire.

 

drain the gas tank, plugs, coils, plug gap

I just put in a set of yoshi cams for a neighbors gsxr750, the bike sat for a month or so while some gaskets and new plugs and coils were on order. I got everything back together and it had similar symptoms. Pulling the bike back apart twice and hours of free labor and losing sleep ... it was bad gas.

 

Definitely get rid of whatever gas is in it first. Other thing would be to pull the plugs you just put in, check the gap is correct as well as whether or not they look fouled (super dark black) as that would indicate it isn't combusting completely or evenly which could be due to a bad coil.