pics of where you're trying to install the jets, and the jets themselves.
there are long and short keihin jets, pretty sure pwk's take the long ones.
but I doubt the threads are different, just the length they stick down into the fuel ?
you're not trying to put a main jet into the pilot jet orifice ?
I thought it may be possible a 28 pwk takes the shorter main, versus long for the 34/35's, but thats not what I'm seeing.
I googled the part # from carb parts warehouse and it shows the long main, so does the ebay rebuild kits
yep, but that long needle jet extends the whole way up into the carb throat, for the needle to ride in as it move up and down
I'm thinking your not getting it in correctly.
I am really wondering if the bowl is too short. With the needle jet screwed in all the way and the main screwed into that it still won't fit. It hits the bottom of the bowl.