Re: 1974 CB750 electrical problems...
Posted by phayzr on Jun 13, 2011; 8:22pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/1974-CB750-electrical-problems-tp3059640p3060454.html
From: LukeM [via Honda CB750'S] <[hidden email]>
To: phayzr <[hidden email]>
Sent: Mon, June 13, 2011 3:09:01 PM
Subject: Re: 1974 CB750 electrical problems...
When using a car to jump start a motorcycle, do NOT have the engine running. It's not uncommon for a car alternator to put out more amps than the motorcycle can handle. The biggest fuse on the bike is typically 20-25A, and the battery itself is usually rated for 15A as well.
Do any of the "dash" lights come on when you turn the key on? You should see the oil light come on, and go off once the oil pressure comes up enough to close the pressure switch.
If it won't start when connected to a fully charged car battery, it's time to check out all the systems: starter circuit (will the starter spin freely when disconnected from the engine?), charging circuit (needs to be checked once you get the bike running), ignition system (any spark from the plugs when you crank the engine?), fuel system (will it sputter when you add a VERY small amount of starting fluid at the air box?). Make sure battery and ground connections are nice and clean and good and snug when tightened down. Any corrosion will just take power from the circuits that need it.
Find a good schematic of your bike, and trace down as much as you can find. On these bikes, there's usually one chassis ground. IIRC, it's a pretty good sized green wire that bolts to the frame near the seat. Your bike may be a bit different, but there's enough SOHC riders on this forum who can help with your particular bike.
I hope this helps. Reply with some updates.
Luke M
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/1974-CB750-electrical-problems-tp3059640p3060454.html
The dash lights do not come on at all unless hooked up to a car battery.
The guy I bought it from just picked it up from ym office to take it home and get it up and running for me!
Thanks for the help! Ill save this email incase anythign else goes wrong!
From: LukeM [via Honda CB750'S] <[hidden email]>
To: phayzr <[hidden email]>
Sent: Mon, June 13, 2011 3:09:01 PM
Subject: Re: 1974 CB750 electrical problems...
When using a car to jump start a motorcycle, do NOT have the engine running. It's not uncommon for a car alternator to put out more amps than the motorcycle can handle. The biggest fuse on the bike is typically 20-25A, and the battery itself is usually rated for 15A as well.
Do any of the "dash" lights come on when you turn the key on? You should see the oil light come on, and go off once the oil pressure comes up enough to close the pressure switch.
If it won't start when connected to a fully charged car battery, it's time to check out all the systems: starter circuit (will the starter spin freely when disconnected from the engine?), charging circuit (needs to be checked once you get the bike running), ignition system (any spark from the plugs when you crank the engine?), fuel system (will it sputter when you add a VERY small amount of starting fluid at the air box?). Make sure battery and ground connections are nice and clean and good and snug when tightened down. Any corrosion will just take power from the circuits that need it.
Find a good schematic of your bike, and trace down as much as you can find. On these bikes, there's usually one chassis ground. IIRC, it's a pretty good sized green wire that bolts to the frame near the seat. Your bike may be a bit different, but there's enough SOHC riders on this forum who can help with your particular bike.
I hope this helps. Reply with some updates.
Luke M
Back on 2 wheels after a 30+ year break. It's still fun, and just as scary as before. I like it. 
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