View Full Version : cb350 won't idle right with light switch on

04-12-2010, 8:52 PM
i have a 73 cb350 twin that runs perfect besides when the light swtich is turned on. plugs are right on, 190 psi compression both cylinders, just hit 8000 miles.

once the switch is turned on the left cylinder misses under 2500 rpm. the right cylinder works fine. once i open the throttle both will fire once the engine reaches 2500 rpm. when i try to open just the left side carb blade it just stumbles and fires erratically.

i spent all day trying to figure it out. the neutral light dims when the kill switch is turned to the on position but this doesnt seem to be an issue since the bike runs fine with the light switch off.

i removed both the headlight and tailight bulb and it made no difference. i tried multiple condensors including a brand new one and had no effect. swapped between two working coils with no effect. tried multiple light switches with no effect. rebuilt the light switch im using and had no effect. disconnected the elec. start solenoid and that had no effect. checked over some of the wiring, adjusted the points, changed the left hand points then changed to a points setup off another motor, tried a little more advance, nothing has an effect on the problem. also removed the horn and flasher box since neither were working anyway.

i have a couple old regulators in the parts pile and a couple old crusty rectifiers i can try but havent gotten to yet. i also have not got the chance to try a different battery but may be able to by tomorrow. i have a couple spare stators as well. is seems like either the battery or charging system at this point or a draw from a wire somewhere.

im losing my mind with this thing. it's all i have to ride while i build the other bike. anyone have any ideas on what to check so i can ride at night as well as daytime?

04-16-2010, 4:20 PM
The 350 has the crappiest charging system known to motorcycling. There are better stators out there. Try Rick's cycle electrics. If it runs fine with the lights off I think you can rule out a tuning issue. Just be sure the battery is good and there are no shorts or bad connections before you invest in the stator, although it is a good idea anyway if you plan to ride at night.

04-17-2010, 12:04 PM
im waiting on a better rectifier to come in. have some spare stock stators but dont have access to them at the moment. ive noticed after a decent ride with the lights off i can turn the switch on and have no low rpm stumble on the left cylinder. after sitting the battery seems to lose some charge. could be a draw i guess. i may try unhooking the battery overnight and see if it makes a difference. the battery is less than a year old.

04-18-2010, 10:05 AM
Try using a battery tender between rides.

04-20-2010, 11:07 AM
looks like the battery has a dead cell. after sitting on the charger the cell on the end closest to the positive terminal wasnt bubbling at all when all the others were. after charging it it's only putting out a little over 10 volts.

i just got a new rectifier from oregon motorcycle parts and im gonna see how it works with that but the battery may be the problem here

04-21-2010, 8:08 PM
was just riding the bike around and stumble is still there. when idling with no lights battery has about 10-11 volts. with lights on 9-10 volts. when i hit the kill switch the bike has around 10 volts with lights off and 5-6 volts with lights on. barely lights the headlight without the motor running.

even with the lights off and throttling the bike to 5-6k the charging system reads 11-12 volts at the battery. i thought this was supposed to be more like 13-14 volts at this rpm?

does this seem like too much of a draw from the lights or should i change out my battery? new rectifier is in. havent tried swapping stators yet.

04-21-2010, 11:15 PM
13-14 volts is right. sounds like reg/rec

04-22-2010, 5:55 PM
the lack of voltage would be the stator right? i put in a new 42 amp constant use rated rectifier (stock is 12-15) that seems to be working well.

04-22-2010, 9:02 PM
Check ac output from the stator. White to white (or yellow to yellow) on all three legs. Should see above 60VAC at 3-4k rpm. If one or all legs are low, probably a bad stator. Also check for continuity (with engine off) between the legs of the stator and each leg to ground. Should not have continuity on any of the above. If you do there's a short somewhere and stator is bad.

The low 11-12v at the battery while running could be due to that battery. With it being so low and possibly a dead cell, the charging system can't keep up. Get a good battery and check it again. Or I've even run jumper cables from car battery (with car not running) to the battery leads to check charging systems. It's just a cheaper route than buying a new battery and then figuring out that you don't need one.

04-23-2010, 12:57 PM
i did the car battery check. car battery had 12.6 volts. when hooked to the bike the bike battery read 12.8 volts idling. at around 4000rpm i was getting a little over 13 volts. seems like that would be enough so im gonna look into getting a new battery.

im not sure where to reference the alternating current. do i need to pull the side cover or can i pick up the wires coming out of the case somewhere? theres 4 wires, red, pink, green, and yellow going to the rectifier.

04-23-2010, 1:17 PM
Hmm. Let me look into that. I had a slight memory lapse. The older charging systems were a little different.

04-23-2010, 2:52 PM
Alright. I found a wiring diagram here. http://www.oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class

but better yet, I found a service manual here. http://home.comcast.net/~tbpmusic3/CB_CL_SL_250_350.pdf

the charging stuff is on page 108.