For this Saito gas conversion, I ordered from Paragon a 1/4-32 spark plug boot and shroud. (see pic). In this kit, they supply some solder. Paragon doesn't know what kind of solder it is, but I assume it's low melt silver soldera little stronger than regular 60/40 tin-lead. Anyway, no matter what I tried, I could not get this, or any solder to flow the two 45 deg chamfered shroud pieces to flow. Hi heat, low head, medium heat, flux, didn't matter. The solder would melt against the steel shroud, but would not flow. It would just drip off. Very frustrating. If I try even more heat, the silicone boot starts expanding and outgassing, ruining the joint by causing the two pieces to pull apart under pressure from the expanding boot inside. Paragon says I'm the first one to have a problem. Yeah yeah, I've heard that one before.

Anyway, here is my solution that worked fine: Sheath the steel with brass. Find some K&Sbrass tubing (that I KNOW will flow solder), cut a slot so it'll stretch over the existing steel, and braze it on. This works because the silicone boot is not present at this time. Sand and clean it, then sand down the extra protruding brass to reestablish the original 45 deg angle.

Now, just reassemble the whole thing according to the original intent, but now I'm soldering a favorable material - brass. Flow is no problem anymore. Here's some pictures: