The CL TT engines I have use a true venturi with a sprinkler system. The needle assembly is at the rear of the venturi, not in the center.

The Max-II .15 has a large contoured venturi and came with two inserts that fit inside the venturi and are held in place by the needle valve assembly. If you do not have these you have to use a piece of aluminum tubing and fashion an insert...or run pressure.
Try fitting drills inside the needle assembly holes to get the diameter of the assembly you need...or as Clean said, send it to Leonard and he will fit one for you.
What model is the Max .25?

Good luck,
George

Edit: you use one or the other of the inserts, not both at once. They have two different inside diameters.