Motorcycle Repair: CBX Carb Jetting, stock pipes, k n air filter

Question
Hi Jan,

I own a 1979 Honda CBX, serial number CB12019079.  Ir's a great bike with about 16000 miles on it.  I recently installed a set of Delkovic pipes on it and they immediately started to blue.  After about 10-15 miles those pipes were heavily blued.

It's been many years since I've cleaned the carbs and I've also installed a K&N air filter so I wasn't very surprised.

I have restored the bike and don't plan to ride it much in the future, just use it as a show bike.  It needs to run and not blue the pipes.

I have already retarded the timing about 2.5 degrees and did not notice any significant change in the way that the engine performs.  That retarded timing should help keep those pipes cool and doesn't seem to effect the engine much.  It's now a show bike that will never be asked to make a lot of horsepower.

My question is:

I know that I need to clean the carbs and while I'm in there I'd like to install a set of the richest jets I can safely use, so that I won't have to worry so much about re-blueing those brand new pipes that I just spent so much time and effort cleaning.

What jets should I install?

Will I only have to increase the size of the idle jets or will I also have to increase the size of the mid and/or hi jets?

Do the mid and hi ranges feed through the same passages?

Sincerely,

Bob Anderson

Answer
Hi Bob,
I do not know if the Delkevic pipes are made the same way as the original pipes, with a double wall header pipe.  I know that the new Sankei pipes are identical to the originals, and they are quite resistant to blueing...  If you have individual K&N filters, the engine will run leaner and you will run hotter which will give more blueing.  The Delkevic pipes are supposed to be very similar to stock pipes, so the easiest thing to do is to go back to the stock airbox configuration, and use a K&N main filter.  This will bring you back close to stock, and the pipes should stay OK.  The trouble with changing jet size is that this will alter the way the bike performs and could lead to undesirable performance effects; not to mention poor fuel economy.  You have a primary circuit with a #65 jet and a main circuit with a #98 jet.  There is also an idle circuit with a #35 jet.  These circuits play a different role throughout the rev range, so unless you know exactly where you are running lean it's tough to make the call.  Go to a Dyno with lambda sensors if you have access, otherwise go back to stock...  Hope this helps, Jan