warped disc, but which one??

Guys, i'm getting a pulsing through the front brake lever, particularly when travelling slowly when you can feel the brake "grabbing", have tried to free up the bobbins but the problem persists (how loose should the bobbins be? I can rotate them with a screw driver wedged in but not using my fingers).
Discs are within wear limits so don't raelly want to replace both, apart from trial and error is there an easy way to check which one is warped?

dial gauge is the correct way to check but you may be able to check them with a pencil from the fork leg to the disc and spin the wheel.

If you can get the wheel up and spin it then looking edge on at the disk will often be enough to spot it. Has worked for me before anyway and is easy to do.

Thanks guys, I've got a front stand, will give it a go.

I've owned about 12 bikes in the past 10 years. I had this problem with 3 bikes. A 2009 Speed Triple, a 2013 Monster 1100 evo, and this 2007 Superduke 990. What do they all have in common? Brembo brakes. I have never EVER seen this problem on any other of the bikes including some high milleage bikes with cheap brakes. My duke only has 15000km on it, the Speed Triple warped in the first 10000km and the monsters warped in the first 1000km. For high end brakes, they are certainly not the most resistant to warping. Looking to replace them with more durable ones.

I had the same problem with what my shop and myself thought was a defective disc. So we got a disk and installed on the right side. This did not fix the problem. It actually was the front wheel that had the brake mounting surface not perpendicular to the axle. I received a new front wheel on warranty. I suspect more bikes have a incorrectly machined disk brake surfaced. And to top that off my mechanic noticed the front wheel was installed backwards at the factory. There is a little arrow cast into the hub that is hard to see.

Have your mechanic remove the calipers and watch the wheel spin with the disk attached. You will see the right disk wobble.

Good luck

I checked the rotors while riding and they dont seem like they are waved or that they arent mounted perpendicular to the wheel...had this issue on 2 other bikes and the problem was fixed by replacing the rotors. Hopefully i just have one rotor to replace!

Ive got about 500 miles on my 1290 and one of my rotors drags like shit. Pretty lame. Looks like some wave rotors are in the near future.