It could be the clamp catching on the body. You may have to loosen the clamp screw a lot more and use a screwdriver or similar to force the clamp to open further to get enough clearance.
If you are trying to remove it complete with the clamp and advance assembly …… are all fixings undone – including the (often hidden) one under the advance plates and close to the block on the right as you look at it?
B……………
Bernie