I am new to the bike building but wanted to take on a project over winter to keep me busy. I purchased a 1973 cb750 in was not completely put back together but it would at least turn over. I got it home and found out they had the coils routed to the spark plugs backwards. I fixed that and it fired right on up. It backfires when you get it to about 3500 rpms. I thought I was doing great so I then today I fire it up once and now no power to head lights nor will the starter turn over. I am not very good at electrical stuff and need some help. Thanks.
-
Enter the April CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!
1973 cb750 no power to light or starter?? Need help
- Thread starter pdcarpen
- Start date
dan1951
CB750 Addict
Might sound stupid but make sure battery is full charged, If so check the main fuse under the lt. side cover, If all looks good there check the main ground from the battery for solid connection, also look for loose or burned wires by the fuse connections. Does Your oil light, neutral, light up with key on?
I do not have oil light, etc. It did finally start again but now it is doing the same thing. I am now getting a very faint zap sound once and then no power for 20-30 minutes. I have tried a different starter solenoid but that did not work either not even sure if it is any good either.
dan1951
CB750 Addict
You can test the solenoid by removing the yellow/ red stripe wire connected to the solenoid at the connection make sure the bike is in neutral or it will lurch foward. Use a short jumper wire attach to the removed wire to the solenoid to the Positive battery lug it should crank, Sounds like a loose ground wire or bad ignition switch by the zap sound You describe.
dan1951
CB750 Addict
The only thing I can tell You now is use a screwdriver and jump across the two main lugs on top of the solenoid try to stay on the nuts and not the lugs as there will be a small arc that may damage the threads on the solenoid. If it does not crank now then I would say the starter is shot or locked up.
Last edited:
Vicman
CB750 Addict
go back and check battery voltage, then take a look at you ignition switch connection to see if it's corroded.
Thanks, It was a bad ground wire. I do hate electrical. I just ran pressure check (harbor freight) looks like cylinder 1@85 2@120 3@0 4@30. After running cylinder 1 and 2 exhaust hot and 3 and 4 cold. That is not good. Idles rough and fire out exhaust. Thanks again guys for the help. I guess I will have to see what it looks like any suggestions on oversized piston?
Add just a little oil in the low cylinders and see if they come up any. Then double check valve clearances to make sure you dont have some very tight valves. If they still are low you will need to look into the motor. Honda has stock oversize piston and rings, they had 4 sizes but several have been discontinued. Cycle X has stock oversize piston kits and can do the machine work as well. You can also look into going bigger as in 836 or 850cc but you should do other upgrades to take advantage of the increased cc. If all you are looking for is a good stock type rebuild then just do the Honda oversizes.
Similar Threads
