Brazing silver nickel with oxy/acet...poor results....mapp/propane better?

I just spent the past 20 hours brazing a bicycle frame with a good friend who has been brazing for nearly 20 years. He is used to his set up which includes a in-line gas fluxer with oxy and propane/mapp gas. (There's a questions here I'll come back to)... I have a oxy/acet setup with the same inline fluxer. We were brazing bicycle tubing (7/4/7 being the thinest) silver nickel and getting poor results. We could not get a good flow of the s/n and the tip of the torch kept getting dirty...? it would have a build-up of crud that would affect the flame, which also would slow down as if you were slowly turning the tanks off.

First, back to the top. The local weld shops tell me that: MAPP and Propane is the same gas....? I have been told different from others. I have also been told that you can not simply switch over to MAPP/Propane with a oxy/acet torch. That there is a difference in the torches/regulators and you have to purchase the correct ones for said fuel. My friend thinks otherwise....

Any ideas what went wrong? The fluxer is BRAND new, this is the first time I used it. I don't believe that is the issue... maybe not... Why would the tip of the torch get a build up of (lack of better term) crud on it...?

Any and all help welcome!!
Jimmy

Can't comment on a lot of your questions, but for sure on MAPP. Actual MAPP has not been produced in this country since 2008. They sell bottles that say MAPP at the box stores, but if you look you see they are not actually real MAPP.

Don't know how successful you will be with a gas fluxer. Old school pre fluxing of the joints is a proven and simple method though! I seam to remember reading that flame settings are crucial with a gas fluxes, if its too oxidixing flame it won't work!

Have used pre-flux and oxy acet torch for year on silver nickel and have never had a problem. Get a jar of good flux, make sure everything is clean and have at it. Twenty hours to do a bike frame! you got to find a different method.

Although we do not braze or silver solder we used Acetylene for years then switched to propane. There is a difference in tips and regulators. You cannot use an Acetylene tip with propane and expect even fair results.

As metalmagpie stated Mapp to no longer made but it was a good substitute for Acetylene. One company where I worked years ago used it on all their Machine Torches with excellent results. Propane/ Oxygen is not very costly and while cooler you can still generate enough heat to burn steel quickly. I am not familiar with the new substitute stuff but this article seems to be very informative. - MAPP gas - Wikipedia, the free encyclopedia

Walter