Wow, you did everything that I would have suggested:

The basics for a good solder joint are:

1. Clean- both pieces with wire brush or emery paper or similar.

2. Flux - I do both pieces

3. Heat the entire joint- Use Map gas torch if needed. Make sure there is no water in the pipe.

A couple of issues that I can suggest: Be sure to heat the overlapping section of the female part of the joint rather than the lip and keep the torch moving around the joint. This insures that the whole joint area is hot enough to wick the solder when it melts.

There have been times when I had a bad joint that I just tossed the fitting because I was never able to make it work after de-soldering it. I think that the fitting becomes so oxidized from the heat that it's just hard to get the bare copper -- where there isn't any solder -- clean enough again. I hate to tell you that with 1.5 " fittings but I don't have a problem with tossing a 3/4" el.

1.5" might work better with a acetylene plumbers torch. If you are using a benzomatic type torch there may be the problem.

Thanks for the suggestions. I do have an acetylene torch with a rosebud tip. I'll try that and see.

With the cost of copper, I hated to toss the fitting. But after the number of times I have attempted I think I am ready to spend a little more $ if it means a successful joint. Maybe I can put the old fitting on a shelf in the garage and after a little 'convolesing' it will work for another project...

Is it possible that you have some moisture present? It only takes a drop or so to cause a void in the sweated joint.
Pressure inside a pipe from heating it up without being open to vent can cause the solder not to wick uniformly.

Acetylene and air (turbo) torch or a larger torch with propane.
Even with a turbo torch you will need a pretty decent size tip.

One afternoon I started a run of 1.5" copper. Things went pretty well (I was using an oxy-acetylene torch) until near the end. I could not get the last two fittings to sweat. I called a friend who is an expert. He and I tried every trick in the book. We were melting the solder out of nearby joints so we had to use dripping wet rags to wrap around the pipe on both sides to stop the heat from spreading.

Finally he asked if I had any liquid solder. I'd never used it. We ran out and got some at 10PM, just making the store. When we got back, we wire brused and used grit paper then fluxed, even with the liquid solder.

We applied it on both the pipe and the fitting. It only took a tad of heat and we had a perfect joint, sweated all the way through.

A few things I learned that night:
1) You can get the copper TOO hot as well.
2) open the spigot - you don't need pressure in the pipe
3) If there is any water leaking through from the other end, use plumber's bread to stop it.

Thanks again for the additional suggestions.

A few of you have commented on water in the pipes. That is not a factor here - this is new construction with no water or pressure present. In fact, this particular grouping of fittings is joined with a union so I am not soldering it in place.

I have not tried the liquid solder. Not something you see at the big box retailers so I'll have to check out a more dedicated plumbing store.

I did buy a new fitting this week and will try it as an alternative.

I'll keep you updated. Thanks.

If you do not want to purchase or rent a larger torch, get a second torch and enlist some help.
Even two small propane units should handle 1.5 inch.
I have a multi-head oxy-acetylene monster that allows brazing of 6 inch and up. You can practically watch the gas tank pressures drop when using it.