Hi there,

I have a 98 CBR900RR with just over 30,000 km. When its warm and while its idling, it sounds like it might be missing. When on the throttle, the bike seems to work just fine, and never has any hesitation. I can also smell fuel quite strongly.

Using an IR thermometer I did a little test. I started the bike and let it warm to 130F. From right to left, when you're sitting on the bike, the temperatures of the headers were 240C, 320C, 340C and 180C.

When I blip the throttle, the RPMs return to a steady idle, rather than dipping below and then returning to a steady idle.

Could I be running rich on the outside cylinders? Would that account for the smell of fuel?

If one or both of the coils were bad, would the miss occur throughout the RPM range?

Any thoughts and assistance would be greatly appreciated! I am no mechanic, but don't mind tinkering. Just thought I'd ask in case my logic is out to lunch before I waste my time.

 

Hi you could always do the Primary/secondary coil test as 1and 4 cylinders are off the same coil, if that proves right then you have to look at the carbs, maybe even a sync of the carbs could help as number 3 cylinder is the base for sync , get the plugs out and have a look at them see what colour number 4 is

 

Thanks for the input! I didn't realize the coils split across the cylinders like that. What sort of readings should I get on my multimeter?

I'll start with inspecting the plugs... running rich would be brown and smell like fuel? Running lean would be black?

If a coil is indeed bad, I would have thought I'd experience a definite miss regardless of the RPM range. Does that make sense?

 

Hi your primary windings should show 2.5 to 3.2 ohms, the secondary should show 21 to 27.The plugs if running rich will be black ,if lean will be white

 

Thank you! I'll report back with my findings when I get time to dig into it.

 

Hi again,

What are your thoughts on these plugs. Photo 1 is from a cylinder that I suspected was running rich, photo 3 is from a cylinder I suspected was running lean.

Photo 1:
https://i.imgur.com/9dbPvUj.jpg

Photo 2:https://i.imgur.com/uN9A1yQ.jpg

I will attempt testing the coils. The problem is that a previous owner seems to have done a seriously pathetic electrical job. Perhaps that's the source of my problems anyway!

Thanks

 

From looking at that picture number one picture definitely rich, second picture from that angle looks not too bad, definitely need a coil test

 

Thank you!

I've attached some more photos for the coil test. Seems a little more complicated than the instructional video I watched here:
https://i.imgur.com/dHlVUJT.jpg
https://i.imgur.com/728lXCn.jpg

There are two, 2-wire connections going into each coil. I am having a hard time finding where to test the resistance due to the electrical work that's been done to the bike already...

 

Nevermind, there are two 1-wire connections entering each oil. I am getting 3.2 ohms for the primary for both coils, but don't get anything on the secondary...

Looking like I better order up a new coil

EDIT: I'm not sure I'm doing the test right. I can't get any secondary resistance for either plug using either coil. Surely if both coils were bad, I wouldn't be able to start and run the bike at all.

 

For the secondary test , put your multimeter probes into the two spark plug ends for the same coil. one in each plug cap