I hope this isn't a topic that has been beaten to death, but my wife's 1200C idles rough when it warms up. It sounds like a miss in the rear cylinder I have tried every kind of jet combination imaginable, new plugs (twice) And i just can't seem to figure it out. As soon as you crack the throttle or raise the idle it smooths out. Any thoughts or experiences with this. I am sort of reluctant to take it back to the dealer because I know its gonna cost me an arm and a leg, but if I can't figure it out soon I'll have to.

 

For starters,

When it is idling rough, try pulling the plug wires one at a time. If you find one that doesn't make the problem worse when you pull it then you likely have a plug wire or coil problem.

If that doesn't work, try spraying WD40 around the intake manifold when it's idling rough. If that causes a change in RPM you have a vacuum leak.

 

make sure you do not have a air leak in the intake manifold...i usually use a small propane torch (unlit) and open the gas just a little and wave it around where the manifold connects to the jugs or the rear of carb and see if there is a rise in rpm or a stumble...i prefer this over spraying chemicals that could potentionaly leave marks/residue on surfaces.......i have used the propane gas method for years to track vaccum leaks in cars with great success.

 

I have already checked for vacuum leaks, I guess next will be plug wires. The rear cylinder is definately the culprit, I just hope its not an ignition module. The rear cylinder is also slow on firing sometimes on start-up.

 

The information provided is rather limited and it also begs some questions relative to why. If the engine is missing at idle when hot, why would you think it was a jetting issue? Especially when we must assume (I know, a bad word) the bike was at one time running fine with the jets you had before the miss started and it doesn't miss when cold even on the jets that are in it now. The wrong jets can do a number of things but they would have to be way way off to cause a miss. Plug wires are almost bullet proof in these days of electronic ignition systems but they are not exempt from thermal breakdown. The same would hold true for the modern coil.

Testing for a vacuum leak can be done without spraying WD40 all over the place. If the jets are right or at least within a factor of plus one to the factory you can simply spray that WD40 down the throat of the carb and if that idle smooths out you have it. If not, it's not a lean condition caused by the vacuum leak. If the wires are breaking down due to heat, this too can be tested by putting the wires in an oven and bringing them up to temperature. If you check them with an ohm meter and there resistance is above 16 or open, junk that wire. In reality what you need is a scope at the time the rough idle is occurring. Don't rule out a bad plug either.

 

if you do not have a dvm, flip flop your wires on the coil and plugs, if the problem moves to the front jug then you def have a bad wire, or just go down to the dealer and pick up a set, they cannot run but what $15-20 ... might be worth getting anyways since you just bought new plugs....also make sure your plugs are correctly gapped. could also be a coil (unlikely but they do occasionaly go bad). personally i'd just go get new wires and start there.

 

Are there any stored diagnostic trouble codes (DTC's) ???????????

 

Have you checked the gasket between the air cleaner back plate and the Carb? I've had to replace that gasket twice on my 06. Causes all manner of spits and farts at idle when that gasket is bad.