I’m restoring a M159, how are you guys going about cleaning the inside of the pipe and muffler? Caustic soda? Are there other ways that work well? 
 

mike 

There is no point using caustic soda in the muffler of the front pipe as there is perforated tube in there with packing around it, the packing witll either have been blown out or be completely gummed up with old residue. If you're lucky it will be the former as it is far less messy to sort out. It has to be cut open, anything left of the packing needs to be removed, the perforated tube cleaned out, new packing added and weld back together. The same applies to the rear silncer, the lower part of which up to the top of the shock absorber is also packed

Thanks, ya I was wondering about that