[71gtx]

Hey guys, I gotta problem on my 81 Honda cb 900c. Probably could be directed just like a cars problem so maybe I can get some help from you guys.

I went and picked up the bike from a trustworthy guy, he said it needed a tune up. Rode it around the block and noticed the throttle response was off, I would give it gas and it would take a few seconds to catch fully. Well it was a good deal and I like workin on stuff so I took it.

Got it home and wouldn't start. So I charge the battery for a few minutes. Starts right up. I let it warm up for about 10 minutes and take it down the block. Keeps hesitating like before. Only now I came to a stop sign and when I started off in first it completely died. Wouldn't crank over, battery dead.

I jump started it, rode it home and let it warm up for about another 45 minutes, thinking maybe the battery needed charging. Put it in first gear and gave it the slightest gas and it died even before I let the clutch out any. Battery completely dead once again.

Sound like an alternator????????????????

[bracketeer]

If it was a Harley I would know exactly what to do but since it isn't...

If it uses generator instead of alternator. Field windings probably need to be re-polarized.

Check battery voltage. Below 12.5 is dead battery. Charge battery. Check voltage. Should be 12.5 to 13.5. Start bike. Voltage should increase to 14.5 or higher. If it doesn't you have a charging problem. If it does you have bad battery.

If it is charging problem. Make sure field windings are getting power. Check voltage at alternator. If it is no higher than battery alternator is bad. If it is higher than battery. Then charging wire from alternator to battery is bad.

[302 Z28]

I doubt the alternator is shot, but it is possible. The more likely cause is the solid state voltage regulator. The silicone rectifiers are notorious for going out in those.

Vince

[71gtx]

I bought a multimeter and need to use it to check the regulator. I have a 79 Honda as well and have been swapping a few parts but same results. Batteries swapped and I get the same problem. Regulators swapped and same problem. How should I test the rotor or anything else with the multimeter to see whats bad?

I used the ohmeter to check the regulator the other day but realized today that I was testing the ports going the opposite way from the regulator instead of testing them directly to the regulator. I dont' know if this means anything but when I tested the wrong ports I received readings on the meter for 2 out of 3 yellow wires over and over again using different grounds. instead of all 3??? Same problem with the other set of wires asked to remove.

Once again charged battery fully and started, ran for a awhile and dead when restarted.

This may sound confusing but hell I am too!!

I dont want to just go buy parts because unlike a car they cost 3 times as much and are 3 times as small!!

[NorthStar]

I dont want to just go buy parts because unlike a car they cost 3 times as much and are 3 times as small!!

I know what you mean. Honda dealers mark parts prices up 100% some places even more!

I really like those older CB Hondas so Ill break out the book for you.
Plus Ive got to fire my bike up in a couple months if spring ever comes.



Try this check voltage of your fully charged battery after its sat for awhile then start it up and see what voltage is. Should be able to maintain 13+ volts at 3000.


Rotor testing.
Slip ring to slip ring should be 3.6-4.4 ohms.
Either slip ring to ground should be infinity.


Stator testing.
Between any of the 3 yellow stator wires should be .41-.51 ohms.
Between black and white wires should be 10-12 ohms.
All should be infinity to ground.


Regulator testing.
Theres two connectors. They also talk about 1981 and newer regulator vs earlier each has a different test method.

Negative on green and positive lead to each yellow all must be same .5-50 ohms. Now reverse leads and they should all read infinity. (3 readings)

Positive lead to red/white wire and negative to each yellow and the green one too, they must all be same too .5-50 ohms. (4 readings) Now reverse leads they should all read infinity.

I should bail now this is getting complicated.

Negative lead to black wire positive to white should be 1-50 ohms. Now positive lead to green shoud be .5-20 ohms.

Negative lead to white wire and positive to black wire should be .5-30 ohms. Now move positive lead to green wire should be 1-50 ohms.

Negative lead to green wire and positive to black wire should be .5-20 ohms. Now move positive to white wire should be .5-30 ohms.

Man this is crazy.

Positive lead to black wire and negative to white should be .5-30 ohms. Now move negative lead to green should be .5-20 ohms.

Positive lead to white wire and negative to black should be 1-50 ohms. Now move negative to green wire should be .5-30 ohms.

Positive lead to green wire and negative to black should be .5-20 ohms. Now switch negative to white wire should be 1-50 ohms.

If it gets by all this its good.

And after all this its probably dirty brushes. ha ha
Check your main fuse for corosion too. If it wont get past an idle without stumbling I think you have a plugged idle circuit to boot.

[71gtx]

i have been working on this forever. i finally did do the test on the battery while running to make sure it was a charging problem. turns out its charging fine?????????? i wouldnt have even guessed. so i took it to a private mechanic and he was baffled too. he thinks it could be the starter with a heat soak issue where it gets too hot and cant crank over. but what i was wondering is could that cause it to also die out when riding like it did

[docvette]

Doc here,

Wow! It's Been like a zillion years since I've worked on a Honda....

Does that bike have a DC rectifier mounted somewhere on the frame? If so that May be shot.

When you say the battery is good, can you pull it and put it in the other bike and start that one? Or is it dead there too?

When the engine dies, can you kick or push start it after the starter fails?

What it sounds like to me (If the Battery in fact is holding a charge) Is you have a high resistance (possibly thermal) to the starter / ignition system causing the Coils or coil packs, to slowly lose power and die, and the starter to drop out after it heats up This could be why it misfires and dies when warm.(like a car with no alternator, at night as the battery dies out)

You could also have some bad grounds going on there too, good thing to check clean and burnish while testing the rest.

Does the engine turn over by hand as easily hot as it does when it's cold ? You might want to check that too..It may be heating up and siezing...(SUGAR MAYBE?)

That's about all I can remember on those...

Let us know how you progress...

Doc