QuestionI have an Honda CB custom and she smokes out the left to pipes an she also backfires out the far right exhaust pipe what is going on? please let me know because i am rebuilding this bike in memory of my pop pop because he couldn't get it running. thanks
AnswerCory, given the limited information, any number of things can be happening. Is the smoke black or blue? How many miles on the bike? What kind of maintenance has it had? How long has it been sitting unused? Black smoke is excess fuel, while blue smoke is coming from worn rings and/or bad valve stem seals.
You have to establish a baseline to work from, first.
Valve adjustment then compression test. All cylinders should be about 175 psi. Low ones could indicated the need for valve job and/or rings. If compression is uneven/low then all the troubleshooting and tuning in the world won't help.
You didn't give the year of the bike, so I don't know if it has the automatic fuel shutoff system or not. If the diaphragm fails in this system, then you get limited fuel supply to carbs.
Have the carbs been left with old gas in the bowls for long periods of time? If so, then the carbs need a thorough cleaning. Check the air-cut valve diaphragm for tears/pinholes. When the diaphragm fails, you get an air leak into that carb and lots of backfiring and poor idling.
The ignition system is battery powered, so a fully charged battery is a MUST. If the charging system isn't keeping it fully charged, then you have a different issue to deal with. The ignition system is also controlled by spark modules which can fail. Try swapping them to see if the "problem" changes from 1-4 to 2-3 cylinders. Spark modules are back by the battery and often look melted on the outside after many years/miles.
You should check the spark plug caps for about 5k ohm resistance. Looking at the spark plug can give an indication of what is going on inside the cylinders.
A factory shop manual will help get you through a lot of the many steps of troubleshooting.
Bill Silver
