QuestionHello there, werkin on a 79 Honda 500 Custom. It idles great, but when I rev it up just a little the left cylinder misses 9 of 10 times.. Then it will backfire very loud..
So far ive..
Changed the plugs.
Swapped the Coils.
Changed the battery.
Used an oscilloscope on the CDI output. (Pulses nicely)
Cleaned the carbs 3 times, and even tried switching all the parts from one carb to the other.
Compression test shows about 50 pounds on each cylinder.
Although the tester had to be modified to work with the metric plug, so this may be inaccurate. However they both give the same reading..
Some ideas would be greatly appreciated.. This thing is driving me nuts already =)
Thanks in advance, Mike
AnswerMike,
does it improve if you partially choke the air
intake? It sounds lean, did you soak the carb
in carb cleaner?
Here are some suggestions that might help:
-backfire indicates faulty ignition or lean mixture.
-compression should be above 150 psi.
-check for faulty fuel petcock or fuel supply.
-sticky carb slide or spring tension too high.
-stator wires should be clean and tight or soldered.
-check plug cap resistance, under 5k ohms okay.
-check any air leaks around intake or loose vacuum or emissions hoses.
-exhaust header air leak.
-air cut-off valve diaphragm bad.
-bad fuel or water in fuel
-tight valve clearance
-sticking valves.
-carb or tank vent plugged.
-collapsing gas line
-Failing CDI or spark control unit.
-Failing pulser or trigger coil.
Builds CDI boxes: dickinraleigh@choppercharles.com
