Topic: '77 550F Electrical Issues

[mtr]

Hi all, long time reader, first time poster.

I've been the proud owner of '77 550F for almost four months now. I've been fortunate enough to avoid any major mechanical malfunctions, but (as one might expect) I've had a few bumps in the road. The one persistent, nagging problem has been with the electrical system. Before I go any further, I'll divulge that this is the first bike I've ever owned; I'm not much of a mechanic to begin with, but I'm learning as I go. Moreover, I know zilch about electronics, wiring, etc. (Also, I searched and checked the FAQs before posting, so hopefully I haven't missed something.)

So, the electrical system... When I made my first pre-purchase inspection of the bike, the seller fired it up without issue. It was the same the following day when I brought my brother along to test ride it. All seemed well with the electronics and charging system. I forked over the cash and my brother hopped on to ride it home (I didn't yet have my license). A mile down the road, we stopped for gas and the bike wouldn't start back up. We got it going with a push start but the battery was toast. After replacing the battery, though, all seemed well.

Shortly thereafter, I began having problems with the turn signals. Sometimes they would work fine, sometimes the wouldn't work at all, sometimes they would blink super-fast, sometimes they would blink super-slow; now they won't blink at all unless I push the switch back and forth manually. I think it's probably the relay that's gone bad, so this might be isolated from the more serious problem described below. Also, my horn, which had worked intermittently at best, has ceased operation.

A week ago or so, the electric start failed to do its job. With the bike in gear, the clutch in, and the button pressed, I got nothing but a dimmed headlight. The button worked fine if the bike was in neutral, though; just not when in gear. I've read about the notorious charging problems that plague the CBs, so I thought maybe they were creeping up on me, or maybe it was the clutch fouling up. Either way, it was on my list of things to take care of. Things got dramatically worse yesterday when I tried to start the bike in neutral and got nothing; the neutral light wouldn't even light up! Luckily, she fired up on the first kick, but I'm beginning to worry that something is dying quickly.

I'm hoping, of course, that this is a common problem with an easy fix that has simply escaped my inexperienced mind.

Thanks in advance for any help!

[bryanj]

You need to check the fuse box connections especially the clips where the fuses fit and all the main connections especially to the ignition switch which is notorious for the block pulling out and the contacts failing,
Also get a Honda manual and check out the charging circuit as per that

[Soos]

Sounds like a old dirty clutch switch.(or broken wire somewhere? anything rubbing through a wire anywhere?)
As well as the neutral switch being dirty.
I've had the same prob on my 650, and cleaning this took care of my problem with my neutral light.
Mine went intermittent, then non-existent eventually cleaned it, problem went away.
Not sure where a 750's is mounted though.


And for the blinkers, I would say your blinker relay is bad.
Plenty of cheap alternatives. Even origional isn't too badly priced. I have one from a auto store. Just a spare at the moment, but have hooked it up and it works well.
3.00, why not? Unless you want to stay original.




l8r

[mtr]

So, could someone share where I might find the clutch and neutral safety switches and what would be the best way to go about cleaning them?

[Spanner 1]

MTR,
I believe your charging system is shot...
All this stuff happened to my '81 CB750k..
I was in denial...just kept charging the battery and riding---until the fateful day  it all just died 70 miles from home !!
Yeah, stuff  will malfunction on the way down, turn-signals etc, the last thing to go is the ignition...anyway, all is not lost , my bet is your battery is not charging, due to a bad rotor ( in the alternator ). You can have it re-wound for about 100$ .
Put a volt-meter across the battery..no ignition or running motor...start the bike and hold the r.p.m. at about 3,000..voltage must rise on the meter or no charge from the alternator... Hope this helps.. from my exp. June '08.

[TwoTired]

I don't know why you call the charging system notorious.  It is quite reliable if not abused.  But, since you don't know it's history, it's best to check it is functioning correctly.  If nothing else, you can add one to the "Known" column of facts. And, can look elsewhere for behavior problems.

Get yourself a multimeter.
Charge the battery and let it rest an hour off the charger.  Measure it's voltage, s/b 12.6V minimum.

KICK start the bike.  And, measure the battery voltage at idle, 2000, 3000, 4000, and 5000 RPM.

These numbers will show if the charging system is working correctly.

Blinkers are voltage sensitive when using the stock winker relay.  A low battery can make them behave oddly.

This charging system is well matched to the stock bike.  If more electrical load has been added (brighter headlight, low ohm coils, dyna ignition, etc.) then more RPM will be needed to keep the battery charged.  Even if the charging system is working properly, the battery does NOT charge at idle with the lights on.  The stock bike needs about 1800RPM to charge the battery, and if electrical changes have been made, the RPM needed to charge the battery will be higher.  If you spend more time at low RPM than at high RPM during operation of the bike, the battery depletes.  The electric start sucks a lot out of the battery (150 amps) and at higher RPMs the battery only charges at 1-2 amps.

The clutch switch is right on the clutch lever perch.

Cheers,

P.S.  The rotor in the alternator is steel and has no windings on your bike.  You can test alternator component with your multimeter, after you determine the charging system health at various RPMs.

[Spanner 1]

Spanner 1  respectfully yields to TwoTired ( if this bike is a magnetic rotor ?) !

[TwoTired]

Spanner 1  respectfully yields to TwoTired ( if this bike is a magnetic rotor ?) !

No, the bike doesn't have a permanent magnet element.  The rotor is steel, magnetized by a stationary field coil in close proximity.

As I understand it, the 81 CB750 has a wound rotor and slip rings like the Cb650 models do.  But, the rest of the SOHC4 alternators have the same arrangement/design basis as the CB550/750.  They are pretty robust, if not abused.

Cheers,

[Soos]

Spanner 1  respectfully yields to TwoTired ( if this bike is a magnetic rotor ?) !

No, the bike doesn't have a permanent magnet element.  The rotor is steel, magnetized by a stationary field coil in close proximity.

As I understand it, the 81 CB750 has a wound rotor and slip rings like the Cb650 models do.  But, the rest of the SOHC4 alternators have the same arrangement/design basis as the CB550/750.  They are pretty robust, if not abused.

Cheers,

Yes the DOHC 750 honda bikes have the same windings as the CB650.
Same taper, same mount bolt used as well.

I can only confirm the '79cb750 having this, as it's the only DOHC 750 I have torn into.
Have read that the '79-'82 DOHC 750/900/1100 bikes all used the same rotor setup.



l8r