If I ride my bike hard, I always get a bit of pre ignition when I turn it of, with loads of smoke out of the a/c, any one know what causes this, and what,s the cure?, is it to do with oil from the breather?

 

If you mean your bike engine continues to run after you shut it off then it's dieseling. This can certainly happen if its running to hot or overheating. Could be caused by a lean fuel mixture and that is not good for your engine AT all

 

There are several things that can contribute to pre-ignition including, a rich A/F mixture, ignition timing, low octane fuel, and carbon buildup on the heads. Occasional pre-ignition on a 1200 is not uncommon, especially in the summer months when the cylinder head temps run hotter, due to the 1200's higher compression ratio.

Number one thing to do is make sure you're running 91+ octane fuel, 93 is better.

Next make sure your A/F ratio is now too rich if you've rejetted the carb.

Then, you can try cleaning your heads by injecting Seafoam or water into the intake. If you don't know what your doing here, talk to someone that does.

Last is timing. Unfortunately, if your running the stock ICM, the timing is not adjustable. This requires replacing it with a programmable ignition module.

It really has nothing to do with the A/C.

 

Added to the above, if you've been running the bike hard, try letting it run at idle for 30 seconds or so before killing the engine.

I didn't completely get rid of the problem until I switch to a programmable ignition and retarded the timing below 1500 RPM.