QuestionI have a 1970 Honda CT90 that runs, but poorly (won’t idle, choke needs to
be on). The engine does not seem noisy and the exhaust smells OK. I want to
check out both electrical and fuel as potential causes of poor running. I am
pretty sure the charging system has been disconnected, and I suspect trouble
because the lights switches etc. have been disconnected. I realize that I could
potentially get the ignition tuned up and run the bike off the 6V battery,
recharging that at night with line power, but I want to get the bike’s charging
system working if feasible.
I have scoured your past answers which I have generally found to be lucid. In
http://en.allexperts.com/q/Motorcycle-Repair-837/1970-Honda-Trail-90-
1.htm,
you briefly outline a stator test and mention the rectifier. Can you either tell
me or direct me to more detailed information on this? And more specifically,
1) can you recommend a manual that would help me with this, and other
testing and maintenance? The only one I have seen online is the Clymer
version that purports to cover about 20 yr of motorcycles; 2) if I conclude the
rectifier is bad, can I replace it with the kind of apparently solid-state
replacement blocks sold at e.g.
http://dratv.stores.yahoo.net/unrec.html
for about $15? Thanks very much for your help.
AnswerKent, here is a good overview of charging systems....
http://www.electrosport.com/technical-resources/library/articles/how-motorcycle-...
The rectifiers are basically one way valves for electrical flow. You can use Radio Shack bridge rectifiers or other ones from other models, as long as you observe the correct polarities in the circuits.
Basically, you have AC voltage being generated in the stator because of the spinning magnetic rotor on the end of the crankshaft. Those voltages are gathered up at the rectifier, which clips off the top of the AC voltages and sends the positive halves to the battery.
As long as the stator leads don't measure any kind of short to ground (stator frame/engine), using a continuity tester, the stators are generally okay. Go here for wiring diagrams:
http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php
Rectifiers are very fragile and if you run the bike w/o a battery or with a dead battery, the rectifier usually dies an electrical death.
When CT90s don't idle it is because of a number of causes.....
*Idle jet plugged up
*Air leaks at intake manifold/carb.
*Ignition system isn't getting 6v to the coil
*Valves are too tight, causing compression loss.
*Ignition timing is incorrectly adjusted. Points must open at the F mark alignment. Points must be clean and gapped to .014" then set the point plate to the F mark alignment. Ensure that the mechanical spark advancer is functioning properly (mounted on the end of camshaft, behind the points).
*Low compression from burnt/tight valves or worn out rings.
Bill Silver
