1979 CB750 Limited Edition

[austin89]

Im new to this. I have a 1979 CB750 Limited Edition motorcycle, i was riding it when all of a sudden it stalled then nothing. It didnt knock or hammer at all, i still had power, but it wouldnt turn over, i could hear the starter engage but it wouldnt turn over the engine. Any suggestions on what could have happened and how to fix it?

[seestheday]

Is the starter not able to move the engine at all?  Or is it moving the engine, but you're just not getting ignition?

Have you checked to make sure you still have spark to all 4 plugs?  I'd start with the basics and work from there.

[austin89]

It doesn't turn the engine at all.

[sgtslag]

Level and condition of the oil?  Sounds like the engine seized up...  Not good.  Unless the battery is dead?  Check it:  should be at least 12.6 Volts, as anything less will not work.  Let us know.  Cheers!

[austin89]

The oil level is fine and good condition. I put a brand new battery in it to check and that's not the problem.

[seestheday]

Can you turn it by hand?  It's an electric only starter, but if you remove the AC Generator cover on the right side of the bike you can get access to the bolt you can use to turn the engine over manually.  I believe it's a 17mm.

Description and pics of the procedure in chapter 3 of the FSM under "Valve clearance" (you need to manually turn engine over to do a valve clearance check).

If you can turn it over by hand then you might have a starter issue.

[austin89]

I will try that and get back to u.

[LukeM]

+1 to SeesTheDay.  I wouldn't think it's seized.  More likely either a bad solenoid or perhaps a locked up starter.

The solenoid is under the seat, near the left side cover.  It should click when you hit the START button.  If the low voltage coil in the solenoid is good, it will actuate the solenoid and close the high current contacts, effectively connecting the battery to the + connection on the starter.  If it doesn't click, then there may be an issue with the START switch or wiring, or the solenoid itself.  You _can_ disassemble the solenoid to clean the contacts, but it may be easier to find a new one and swap it in.  They're cheap enough.

If the starter doesn't go whir, then remove it from the bike (documented in the FSM).  Then take some jumper cables, and connect + on the battery to the + cable on the starter, connect the - to the - post on the battery, and gently touch the other end to the starter case.  It is a high torque motor, so it may jump when it tries to spin.

If it goes whir, and doesn't sound like it's binding, then my first guess would be bad solenoid, or possibly the gear set for the starter (in the left side engine cover) might have some issues: missing bolt, broken gear, etc. Center stand the bike if you are removing that left engine cover: oil will come out.  
If the starter doesn't spin, it's possible the starter guts need to be replaced.  There is a rebuild kit available for these on EBay for not much money. Details on starter diagnosis/rebuilding are also in the FSM.

I hope this helps.  Let's just hope it's something simple and inexpensive.  It sure would suck if the motor is seized, but let's just keep thinking happy thoughts for now.  Good luck.

Luke M

[austin89]

I took the right side cover off and tried to manually turn the engine over. Going clockwise it would turn maybe half a turn and stop and I couldn't go any further, when I went counterclockwise it would go a full turn.