I have my warp threaded 1234, 1234 ... and 1234321 4321 4321. I throw the shuttle from right to left with 12 raised, then 23, 34, 14 and so on. When I want to change the direction in the weft I find that I am not catching the end warp threads if I simply reverse. That is if I am on 34 and I go to 23 (instead of 14) to reverse, I get floats on the end warps. If I go 12 instead, it works out. Or if I break the weft and start on the other side with 23 it works out. I am not able to figure out why that would be. Any help?

I am not using a floating selvedge. I would have, but I saw one of Jane's videos where I thought she said that if you started with 1 on right and ended with 1 of left it would work out. I clearly misunderstood. I have been playing with selvedges on twill with and without floating ends - I can make things work but I have not understood the "theory" to just arrive at the answer (no floats at the selvedges) without trying one of the four options (12, 23, 34, 14 forward or reverse) each time when I reverse directions.

I while ago, I found instructions on how to avoid using floating selvedges on twills. The instructions say "Always start the twill weaving sequence by entering the shuttle on the even side of the warp. The even side refers to the side where the outside thread is threaded in a heddle on an even numbered shaft." This has worked for me as long as I start treadling with 12 or 34 and I continue repeating the twill in one direction.

When I change direction on the twill and treadle, for example, 12, 23, 34, 41, 34, 21 etc., at the turn, the thread on outside edge of the warp(the 4th shaft) gets missed for 3 picks in a row causing the loose thread. I think floating selvage is needed if you plan to reverse direction on the twill.

I have found it helpful to grab a pen and paper and draw a cross section of the weft threads going over and under the warp threads to see what happens. Jane has shown how to do this in a few videos. It just helps me visualize what is happening.