Well, a 155 main is pretty big, hope you have done some mods and are at sea level.
The pilot is a common flat-blade screwdriver tip.  You might as well buy the replacement one before you take the old one out, and you can get a good look at the blade slot then.  Stock US model is 52.5# pilot, if you want to try bigger go to 55#.

A good indicator of overall jetting is the weather...if popping/backfiring increases on humid days, or at higher elevation, that indicates rich....less popping on those days indicates lean.

To test the main, accelerate from 30 or 40 mph, in 4th or 5th gear at full throttle for several seconds, then reduce throttle by about 1/8,...if power increases for a second, you are lean on the main jet.  Go up one jet size and test again.


I actually ended up going smaller on the pilot to a 50#.
150 main jet,  50 pilot jet (I'm at 2600ft and ride up to 9000ft, ) works for me.

Yes, it's a pretty narrow hole, and set up in there a bit,...but use the sturdiest blade that you can get to fit up there, to reduce the chance of chinkering up the soft brass...

  Normally you don't take off the carb to changes the high and low speed jets.