Sometimes you can carry a joke too far. The first time, it gets a big laugh. So you turn it into a running gag. That makes it funny for awhile. But you have to know when to quit, because, if you don’t, it stops being funny and becomes tiresome.

That is, sadly, what happens with Kansas University Theatre’s production of Patrick Barlow’s “The 39 Steps.” It’s very, very funny for awhile. But the jokes just run on too long.

The show is a farcical adaptation of Alfred Hitchcock’s 1935 thriller, that thrusts bored bachelor, Richard Hannay (Seth Andrew Macchi), into a web of intrigue when beautiful spy, Annabella Schmidt (Lindsey Roesti), starts a gunfight at the theater, begs Hannay to shelter her in his apartment, and then is murdered. Hannay is forced on the run from the police and the mysterious espionage organization, The 39 Steps, in a desperate attempt to clear his name.

The stage adaptation is played wholly for laughs. Roesti’s death scene in the apartment is outrageously funny, and she plunges across Macchi’s lap as he sits in an easy chair, forcing him to wriggle out from under her in ludicrous fashion.

The genius of the play is that Macchi is the only actor who plays the same role throughout. Roesti plays two other women with whom Hannay becomes involved during his adventure, and every other character in the show is played by two actors designated simply as Clown 1 (Tim Wilkinson) and Clown 2 (Alex Roschitz). Wilkinson and Roschitz dive into the silliness of switching from character to character (often multiple times within the same scene) with gusto. Both are clearly having the times of their lives as they shift from spies to lingerie salesmen to Scottish innkeepers and even to sheep.

Every one of the four actors is exceptionally gifted at physical comedy. In addition to wriggling out from under Roesti, Macchi manages to flip into at least six different positions while trying to sleep in the easy chair, climbs through a picture frame meant to be a window, and somehow balances his body lying on top of a very narrow crate. Wilkinson and Roschitz often accomplish character changes by switching hats and changing posture, and one particular scene required each of them to play three characters each speaking to the others. They spun and switched hats and wigs so the audience could keep straight who they were from line to line. At one point, they switched off between sheep and spies, dropping to their hands and knees and removing their hats when they were animals and reversing the process when they had a line.

As brilliant as the performances of the actors were, though, the production wasn’t able to sustain the humor throughout. In the first act, the jokes are fresh, and the pace is frenetic. But in the second act, the pacing slows way down, and the gags become tiresome. In particular, any time someone said, “The 39 Steps,” there was a music cue and the actor posed. It was funny at first, but, when it was repeated ad nauseum towards the end of the play, it became tedious.

All of which was a shame, because the four actors featured in “The 39 Steps” are clearly very talented performers, who did outstanding work attempting to bring the show to life. One wishes the slapstick had been dialed back just a bit so that the jokes stayed funny all the way to the end.