Mixture distribution on carbureted engines is always going to be poor so I basically ignore EGT readings during a runup. During takeoff and climbs the big issue is keeping an eye on the CHT’s for all cylinders. A spike in CHT’s needs to be attended to immediately. However that being said if something suddenly changes the engine is probably trying to tell you something
One possibility is that the induction cross over tube at the front of the engine has a loose coupling. The other thing to look at is the baffling on the right side
A check if you suspect an induction leak is too lean the engine during a high power runup until it dies, if the EGT spread worsened as you leaned then it would be worth checking the induction piping. The lower the MP the more an induction leak affects the engine.