Yeah, getting the tubing over the low speed needle is a pain. I use large diameter tubing, and I streach it open a little with some needle nose plyers. I also make sure the needle is clean by wiping down with something to get any oil off. If it's oily, the tubing just slides off. If it's dry, the tubing will grab, which is what you want. It's a pain, but it works.

I haven't tried this or had time to write it up, but you can also remove the O-rings, then wind some thread in the groove, and put on a touch of CA, then put the o-ring back. That expands the o-ring and gets a better seal.

Btw, the Mag engines all seem to come with 2 head gaskets. You might find more power if you remove one. I do it on my .15's, but haven't gotten arond to it on the .28's and .25's I have.