Re: 1979 CB750K wont start

Posted by sgtslag on Jan 06, 2012; 3:50am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/1979-CB750K-wont-start-tp3636825p3637005.html

There are two coils, supplying spark to all four plugs, two at a time.  Two cylinders get a spark on their exhaust stroke, which is harmless, but it draws energy away from the other cylinders, which are firing.  The coils are weak, from the factory, so be sure to test each plug for proper spark.

Are you certain there is fuel/air going into each cylinder?  The rusted tank (since replaced) could have sent bits of rust into the carbs, which you stated you have rebuilt.  I guess I would verify that atomized gasoline is reaching the cylinders.  Can you start it by spraying starter fluid into the carbs (if they fire, then you have good spark, and air)?  Did you replace the fuel filter?  The OEM is a metal screen, sitting on top of the petcock, protruding into the gas tank.  Mine had been removed by a PO, and it took me about a year to discover this.  I spliced the fuel line, and inserted a disc filter into it, to prevent any crud from reaching the carbs.

The '79 DOHC is a great bike -- I love mine, but it gets ridden very little now.  Still, it's rock solid, and dependable.  My wife and I toured on ours, two up, circling Lake Superior, two years ago.  Wouldn't hesitate to take off, cross-country, on it again.  Give the starter fluid spray a try, then report back.  Cheers!