Motorcycle Repair: Honda XL185 exhaust mod, air filter system, street elbows

Question
Hi Bill,

I just bought a 1981 XL185 with a rusted out stock silencer.  I've begun replacing the clunky exhaust system with 3/4" copper plumbing, following the stock routing path through the frame.  I sawed off the final exhaust, just past the headpipe, leaving about an inch of stub which is solidly rusted onto the headpipe.  I hammered/brazed a 1" copper sleeve onto the stub, then reduced to 3/4".  From there I soldered in a stub of copper, two 45 elbows up to the shock, two 45 street elbows to get around the shock, then a 3/4" female threaded fitting.  I bought a mower muffler silencer with 3/4" male threads.  It fits nicely inside the stock bracketed silencer housing, which I'm cutting off and re-using as a mounting point.  I'm using the heavy copper pipe and regular plumbing solder.  Total cost, including muffler is about $20.00.  I'm buying a sock filter, probably UNI filter.  I'm wondering if I'll need a jetting change, or if you have any other suggestions.  A friend has an old mid 70s TL250 carb that I may try to use.  What do you think?  Thanks, John

Answer
John, I admire your ambition for recreating the exhaust system, but fear that it will unsolder itself as soon as you fire it up. Exhaust temps can get into 400-500 degrees, well past the temperature of most solders, plus  the copper pipe will conduct heat like crazy, leading to the meltdown of the leadbased solder. Silver solder or bronze brazing rod may hold up better, but Honda makes exhausts from steel for a reason.

Any changes to the primary pipe lengths and the air filter system usually require a main jet change or two. Get some from the dealer that go up 1,2 and three sizes and just play with it until it runs well at all speeds. You may have to change the needle clip position, too, on the slide.

Changing out to a new carb will put you in uncharted territory of trial/error...

Bill Silver