Yep about the thickness of a credit card but you MUST remove the carb restrictor to do this. If you set it with the restrictor in it your gap will be too big and your going to end up rich on the LSN to compensate.

I actually prefer to bench tune so you know you have it close before you get on the track. After you have the Idle gap set fire up the engine, if the idle is high richen the LSN, if it won't stay running you need to lean the LSN. This will get your LSN set good enough to start tuning the engine in. Now blip the throttle for a minute to get some heat in the engine. Once warmed up give it full throttle, you want the engine to rise in RPM's nice and fast but only max out at about 80% of the max RPM's. If it really screams and does not stop climbing you should richen it up. Once you can hold full throttle and it gets to max RPM and stays at max and does not continue rising your HSN is close. (When I say hold it full throttle thats only like 2 seconds max.)

Now when the engine goes back to idle after that full throttle hold what the idle does will tell you what the LSN needs. If it immediately drops to a nice steady idle and stays at the same idle for 20 seconds then you got lucky with the first LSN setting and your good to go. If the idle stays a little high for 2-5 seconds then drops to a low idle you will need to lean the LSN. If it drops to a good idle for a split second then revs high again you need to richen the LSN. Remember that now as you tune the LSN in small amounts you may need to make very small adjustments to the idle gap.

Now throw it on the track and run... when I said cold blooded I meant that they take a while to warm up.. like 2, 3 sometimes more laps.