Topic: Umm...Electric?

[natron602]

Ok, I hate electrical and may be in way over my head but having never touched a motorcycle I bought this one and two months later learned to do the top end rebuild from arguments in here and youtubes (and it barely leaks). in other words, I'm stubborn as hell and going to fix this myself no matter what.

1975 CB550k

So..where to start... I recently had some melted wires in the sub harness. I replaced those and replaced the rectifier and regulator with the Rick's unit. It's been going a couple of weeks but yesterday on my way to work...it was backfiring and sputtering then suddenly kicked in running fine but then after a few miles I lose half power. I get to work and can touch the pipes for 2 and 3 without scalding my hand so those aren't firing. I figure out the foot that opens and closes the points for 2 and three snapped so they are stuck shut. I slapped the old one in as a temporary fix but still....no get up and go....and a real crap shoot to start.

I found some previously unnoticed melted wires in the main harness this time (surprise surprise it looks like those going to the left coil. So.... I guess I have some wiring to do. But where do I start? Do I just go at it with extreme prejudice, gut the wires all out and start over or try to salvage some? And for the love of god, why can't I seem to find out what gauge to use?

One more thing... I have a bit of a thing with this bike where she likes to have two or more things wrong at the same time which are either completely unrelated or unrelated except in effect so when I think I have found the obvious issue, it still doesn't work until I find the other. What else should I check besides the carbs obviously...it's always the carbs. Any good advice on the wiring also appreciated.

PLEASE!?

[natron602]

Oh and completely forgot to mention the lovely young woman who ran into it with her truck this weekend (tapped supposedly, I was inside the gas station) but she knocked it down good and bent the bars. Maybe related. I also changed the oil the night before the first instance of power loss. You know how changing to summer oil can affect electrical...

[70CB750]

They say that 90% of carb problems is electrical - i.e. people blame carburetors for a lot of stuff.

Check your spark plug cables, also power to coil.  If you swap coils, what happens?   Meaning 1-4 to 2-3?  If the problem moves to the other pair of cylinders, the coil is the problem.  It certainly looks like it.

The coil should be getting power with ignition on and the Kill Switch in position Run.  If there is no power to the coil, make sure the Kill Switch gets the power.  Since 1-4 is firing, Kill Switch should have power, but never hurts to check.

All you need is a ohmmeter and bit of patients, the electrical circuits are very simple on these bikes.

Diagrams:

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php

[calj737]

Exactly what he said. But here's some extra guidance:
The power wire running to your coils is BLK/WHT striped. It comes from the KILL switch as 70CB said. The BLUE wire from your points and the YELLOW wire feed each side of the coils, BLUE to the 1-4 coil, 2-3 by YELLOW. These are not the source of the melted harness.

If your pipes are cold, then the spark plugs aren't firing. If it were only a fuel issue, the pipe would still be somewhat hot. If this issue began after the gas station collision, or worsened, then I'd start carefully disassembling the switch controls from the bars. Inspect the wires themselves and make the insulation is covering it completely. Especially look under the instrumentation cluster as this is a popular location for bare wires to ground out.

More times than not, a PO improperly jumped the bike and reversed polarity. This frequently results in a melted harness. Since you replaced your R/R, I suspect that to have been the case.

So, start at the coils on the BLK/WHT wires for voltage and poor connections. Work your way back to the handle bars. Then trace BLK from the handle bars thru the harness to the KEY. Somewhere along that line is the drop in voltage if you find the coils are problematic.

Best to replace your points with a quality set of TEC brand only. Avoid the Daichi points. And carry a spare set until you've got the bike running really well for a while. Condensers should be replaced too.

[natron602]

They say that 90% of carb problems is electrical - i.e. people blame carburetors for a lot of stuff.

Check your spark plug cables, also power to coil.  If you swap coils, what happens?   Meaning 1-4 to 2-3?  If the problem moves to the other pair of cylinders, the coil is the problem.  It certainly looks like it.

The coil should be getting power with ignition on and the Kill Switch in position Run.  If there is no power to the coil, make sure the Kill Switch gets the power.  Since 1-4 is firing, Kill Switch should have power, but never hurts to check.

All you need is a ohmmeter and bit of patients, the electrical circuits are very simple on these bikes.

Diagrams:

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php

Love that quote about carbs. Gonna have to remember that one. I meant to ask about that. At what spot exactly does one switch the coils? At the points? the actual wires for the coils?

Also last night the power issue was still very definitely there but all the pipes were hot. I have blisters on my fingers to prove it despite shelling out a few bucks for one of those laser thermometers. Always forget I have it until my fingerprints are burned off.

[natron602]

Exactly what he said. But here's some extra guidance:
The power wire running to your coils is BLK/WHT striped. It comes from the KILL switch as 70CB said. The BLUE wire from your points and the YELLOW wire feed each side of the coils, BLUE to the 1-4 coil, 2-3 by YELLOW. These are not the source of the melted harness.

If your pipes are cold, then the spark plugs aren't firing. If it were only a fuel issue, the pipe would still be somewhat hot. If this issue began after the gas station collision, or worsened, then I'd start carefully disassembling the switch controls from the bars. Inspect the wires themselves and make the insulation is covering it completely. Especially look under the instrumentation cluster as this is a popular location for bare wires to ground out.

More times than not, a PO improperly jumped the bike and reversed polarity. This frequently results in a melted harness. Since you replaced your R/R, I suspect that to have been the case.

So, start at the coils on the BLK/WHT wires for voltage and poor connections. Work your way back to the handle bars. Then trace BLK from the handle bars thru the harness to the KEY. Somewhere along that line is the drop in voltage if you find the coils are problematic.

Best to replace your points with a quality set of TEC brand only. Avoid the Daichi points. And carry a spare set until you've got the bike running really well for a while. Condensers should be replaced too.

The pipes were warm I guess but I could touch them without injury.

And...this is the only time this is ever going to happen.... I reversed the polarity.... There was a pretty girl involved, I may have been distracted doing the cool guy motorcycle lean... But I will say pretty much everything on the bike has been the POs creative rebellion against the oppressive ideals of Japanese engineers and I suspect the wiring is no different. For instance the orange wire is clipped because..... running lights, who needs those?

[70CB750]

Switching the coils:

- swap spark plug cables 1 for 2 and 2 for 1.
- swap spark plug cables 3 for 4 and 4 for 3.
- swap points wires blue for yellow.

[natron602]

Switching the coils:

- swap spark plug cables 1 for 2 and 2 for 1.
- swap spark plug cables 3 for 4 and 4 for 3.
- swap points wires blue for yellow.

Super appreciated, sir.

[natron602]

I didn't switch the coils yet, but I'm a little lost. What this wire do? I mean it's a ground but from what? I'm not ready to unwrap all the tape yet to trace it but it may be the only one melted.

And strangely spark tested...and 2 and 3 had spark. 1 and 4 were wet and no spark even when I switched the plugs. All were a bit black on the end.  So, uh...did I mention I'm confused?

[calj737]

That ground wire is not stock. No telling where it's heading to.

You switched plugs or plug wires? If wires, you also need to swap BL/YL wires at coils

[natron602]

It was getting a bit stormy and I was exhausted so I didn't get that far yet. I just switched plugs and sparked against the engine to make sure the plugs weren't dead.

[calj737]

Gotcha. I'd move towards evaluating the coils. Pretty unusual for plugs on the same coil to go bad.

[natron602]

So this may be a stupid question but it's one of those little things where it's assumed everyone knows I think so I can't find the answer. I've been connecting the point and condenser leads the way I took them off but I'm curious if they're correct. How exactly should they go in relation to the washers and where they hook up?

[mystic_1]

So here's a picture of a single point:



The body of the point itself is connected to ground.  The screw post is the connection point for both the condenser, and the lead going to the coil.

If you look closely at the picture you can see the insulating washers that keep the screw from touching the body of the point.  These even have little shoulders on them that go down into the hole in the point body, so the screw is centered in the hole and not touching at all.  On the other end of the screw, the point spring is part of the circuit and carries the power do the point's arm, through the contacts, and to ground when the points are closed.

Stack the spade connectors of both the coil wire and the condensor onto the screw stud and then put the washers and nut on.

Like this:



Hope this helps.

mystic_1