QuestionHi first off let me say thank you for taking the time to read my question.
i installed a new wiring harness on my 1975 honda cb750 as well as a different engine of same year, the starter relay was not working properly so i jumped in for the purpose of seeing if the bike would start and run. i have power to the coils as well as power to the each side of the points (alternating from side to side as the engine turns over) but no fire at the spark plugs or from the plug wires at all. i put on a different set of coils, new plugs, plug ends, and new wires. same problem. What could be wrong?
AnswerJames, check the primary resistance in the coils.. and the secondary resistance between the two spark plug leads with no plug caps installed.
Then, check the plug cap resistance values... should be around 5k ohms.
When checking spark, BOTH plugs have to be connected and grounded to the block, to complete the secondary circuit.
CLEAN the points thoroughly, gap to .014" or so, then set to open at the F marks for 1-4 and 2-3.
While you are cranking the motor over checking for spark (leave the plugs out on the block, so it is easier on the starter motor), watch the points as they open and close. If you see heavy arcing, then the condenser is bad on that side.
Points are just a switch to turn the coils on and off. The point faces must be clean and shiny, so the coils can get full saturation when the points are closed.
Make sure you have close to battery voltage at the coils + side. Check the kill switch for corrosion that could reduce the voltage to the coil primaries. Put an amp meter across the points and watch to see how much current each side is drawing. Both sides on all tests should be close to matching the other side/set of components.
Bill Silver
