| Author | Message | ||
     Natexlh1000 |
I know some of you persons know a thing or two about other bikes. My uncle's 1978 CB750 supersport won't charge its battery. Is that charging system the same as our Buell charging system? (and yes I planted the seed that he NEEDS a XB9) | ||
| Race_pirate |
Its usually the stator and/or the rotor. Had a buddy with the same bike, which broke down at Laconia Bike Week and we had an interesting time getting parts. Read this - hope it helps There are 3 or 4 parts to the CB 750 charging system: Stock: 1. Stator Bolts to the inside the left side engine cover... 2. Field Coil Also bolts to the inside the cover (the smaller of the 2 pieces) 3. Rectifier Finned unit bolts under the seat/side cover 4. Regulator also bolts under the seat/side cover when the key switch is turned to on; battery power is fed to the regulator. The regulator controls how much voltage gets fed to the field coil. The field coil is basically an electro magnet... the magnetic field created by the field coil is transferred to the stator... the serrated metal rotor that bolts to the crankshaft rotates between the field coil and stator... as the rotor spins, the serrated portion causes the magnetic field to pulsate... this pulsating magnetic field is picked up by the stator and sends pulses of AC voltage to the Rectifier... There are 3 separate windings in the Stator... 3 yellow wires coming out of it... The rectifier changes the voltage to DC and sends the current thru the regulator to the battery... Depending on the state of charge in the battery and the draw of current required by devices using the power (lights, coils etc.) the regulator figures out how much voltage gets sent to the field coils... the more power required, the more to the field coil... the more power at the field coil, the stronger the magnetic field... the stronger the magnetic field, the more voltage made by the stator... Key switch off you should have 12-13 volts at the battery... Start the bike up and rev to 2000-3000 RPM, you should have 13.5-14.5 volts at the battery.... To test the field coils and Stator, disconnect the wire plugs that go into the left side engine cover (stator & field coil wires) should be 3 yellow wires, white wire and a green wire... The green wire is the ground for the field coil, run a jumper to a ground or to the negative terminal of the battery (-) The white wire is the power wire to the field coil, hook a jumper to it and long enough to go to the positive terminal of the battery but do not hook it up yet... hook the positive lead of a multi meter up to one of the yellow wires with the meter set on AC voltage and the negative lead of the meter to a ground. Start the bike up and hold at approx 3000 RPM... Hook the jumper wire for the white wire to the positive side of the battery. Read the voltage output on each yellow wire... It should be 40-50 volts AC on each wire... If so, no sense in pulling the left engine cover off.... IT SHOULD HAVE OIL IN THE LEFT COVER. So if the stator/rotor test was good, the problem is the Regulator or rectifier... | ||
| Natexlh1000 |
OH! so it's the same as an automotive-style alternator. Makes more sense than the "waste the extra" version we have. Thanks a lot! I'll send this info along to me daddy's bruddah. | ||
| Tramp |
before you go ripping stuff apart: (I have a customer's '78 750k in injunmort's garage at the moment) is the battery new? (& i don't mean new two years ago, never run, etc. i mean 'new') the VRs go more commonly than stators/rotors on those 4s. first start with battery condition. | ||
| Smitty808 |
I'm with Tramp! Check the battery first. I work on those all the time,(I'm a Honda service tech)and 90% of the charging problems I see are bad batteries. After you make sure the battery is good...then carry on with Race_pirate's suggestions, they are right on track! If you end up needing wiring diagrams or anything...let me know I can probably scare some up. | ||
| Race_pirate |
I cannot take credit for the info above, its what we used to get my buddies CB going. Heres a link to the wiring diagram CB750K1 I agree with the battery first, I only assumed that that has been checked already. I worked on an XS650 recently which is known for one of the worst charging systems known to mankind... http://www.slickschoppers.com/TechArticles/Wiring_Diagram.html | ||
| Bluzm2 |
Race, I'll second the XS650 issues! But, they're not as bad as the "Prince of Darkness" aka Lucas! If memory serves, the 650's has a selinum recitifier under the battery. They were prone to vibration failure. Hmmm, lets see... 650cc twin, vibration sensitive components, think there could be a problem? I went through more than a couple of them.. | ||
| Race_pirate |
A few years back I had bought a Running XS650 for $75 It ran great, had kick and electric start... and a center stand. I had cleaned the carbs and was in the process of adjusting them while the bike vibrated all over my fathers driveway while on the center stand. I have yet to feel a bike that vibrates like that!!!! I sold it a month later for $250. | ||
| Bomber |
650s weren't TOO bad if you carried a pocket full of brushes with ya -- they had quite an appetite for em | ||
| Buellbozo |
just my two cents...i have had older honda charging issues turn out to be low magnetism in rotor,and around these parts,ALL old honda rectifier are suspect.i'm an electrical idiot,but that's what i've run into. on another reference-Prince of Darkness-prehaps Rocket or other British gentleman could tell me...Is it true ya'll drink warm beer because of Lucas refrigerators? expiring minds want to know!  |
