KZ 750/Blue Pipes/black plugs/Blue Owner

I'm stumped. I'm the original owner of a '78 KZ750 twin. The original pipes rusted out after 6 years and the exhaust was replaced by my dealer. He installed a 2/1 Winning exhaust. I was never that crazy about the look nor the sound of the exhaust. I gave the bike a good once over this last season and felt a new Mac 2 into 2 would look better. I replaced the exhaust and the new tubes quickly turned deep blue. My plugs are usually black. I replaced them with the one hotter recommended in the service manual. The bike smells rich. Everything I read seems to indicate the bike should be running lean. I'm looking for help!

You are making an assumption that the MAC pipes flow better than a stock set up. This is not necessarily true. MAC systems are low-end and I doubt have much engineering in them and as a consequence, may not flow as well as the stock system. Also, the black plugs? Are these sooty or oily? Sooty means incomplete combustion... lack of valve clearance, ignition timing, low voltage at the coils, points gapped incorrectly; some or all these things may be the issue rather than the carburetors but you could have a dirty air cleaner, improperly adjusted float levels or dirty carb internals causing the issue. Oily plugs indicate poor ring sealing or cylinder head issues. You have a 30 year old air-cooled bike. An air-cooled bike is low tech and easy to work on but needs attention to keep running well. Get a factory shop manual or Clymers and go through the tune up steps in the order that is suggested (it is counter-productive to do the steps out of sequence) and see if this doesn't cure your plug issue; going to hotter plugs is not the way to address this type issue; maintenance generally is. In addition, check your coil voltages. Low voltages will leave your plugs fouled. See our website for a tech tip under "wg's Tech Stuff Index" on Coil Repowering.

Can't add much to what WG says. He's one of our greybeard experts.
But black plugs and blue pipes may not be related.
Chrome turns blue with heat. Thinner walled pipes will transfer the heat to the chrome plating more quickly, and they'll turn blue. Even with black plugs, your engine may be putting enough heat to the pipes to turn them blue. Just a thought....

Sorry I didn't address this issue. LTD is totally correct... the single wall MAC pipes will blue regardless of jetting as will most any single wall pipe. On cruisers where "pretty" is important, they use double wall tubing... that is, one set of tubing inside another; what amounts to a complete heat shield on the outside so while the inside tubing that carries the exhaust is as blue-black as can be, the outside will look pretty and the chrome stays fresh.