Low RPM misfire

[FastCurrey]

Last week I began to experience what feels like a misfire when running at low RPMs (approx. less than 3.5K) and the bike is at operating temperatures. When I got home I pulled the plugs and all but #4 Cyl looked fine; #4 wasn't bad it was just darker with a hint more buildup. I replaced the plug with a brand new NGK CR9E, the same as what came out of that cyl. The next day I took her out and thought every thing was peachy, figured I had a bad plug that finally petered out but when the bike reached operating temperatures the sputter came back. I notice it when I leave the line from a stoplight or doing a slow roll through the neighborhood.

As I am writing this I begin to fear a coolant leak into a cylinder. Once the fluid begins to flush through the jackets it leaks into #4 causing the sputter and higher RPMs clears out the coolant faster than it can be replaced. Please tell me I don't have a leak.

My first thought is a coil has gone bad/ is going bad. This problem seemed to crop up after sitting at a light on a hot day and the heat was roiling up, I fear heat may be causing a coil to misbehave.

Anyway, I did a search for low RPM misfires and didn't have much luck so please don't set me on fire. I hope someone can provide some genius insight as I am on a tight budget - recently retired from USAF after 21 years - so I don't have much cash on hand. I am not afraid to dig into the motor and have a maintenance background.

Bike stats: '05 Busa with Power Commander V and Brocks Street Meg Black Full System 20" Muffler both installed May 2011. I have also done the air box mod and pair valve is blocked off. I haven't had issues until last week.

Any help or suggestions is appreciated.

:1zhelp:

 

[dadofthree]

You could swap coils from cylinder to cylinder and see if the problem follows the coil pack. PM GIXERHP, he knows a little about bikes.

 

[PA99Busa]

I had the same issue, swapped coils and all is well. I suggest finding a working set and try them out.

 

[FastCurrey]

Thanks gang. I was thinking coils too. Once I get around to it I will perform that maintenance and let you know.

 

[GIXERHP]

The first thing i would do is swap coils, and see if the problem moves, easiest!
If the problem persists, then you need to look further such as compression test, and leak down test.
Is the bike losing coolant? If you are losing coolant , it should cause the plug to foul, at some point.

 

[FastCurrey]

Here is the rundown so far: I narrowed down the coil I thought was going bad by looking at the plugs and choosing the one with the most "gunk" or sooted deposits. I replaced the plug and coil but the problem didn't seem to correct, it wasn't as bad but it still existed. I purchased new coils for the remaining cylinders and replaced them all. The problem seems to have cleared up but the weather is cool so heat isn't an issue. Further testing is required but I hope she is fixed.

I will post an update after a couple of more rides.

 

[dadofthree]

Hope you got it