Topic: first ride: 1976 CB750F. now tuning / charging issues

[riffman12]

so today was the maiden voyage of my bike. Still needs paint, but wanted to get it running right before then.

The ride started out pretty well, bike started easily with a little bit of sputtering and backfiring here and there as I messed with the mixture screws. Here's the first tweaking stop:




Then things started to go south. I was doing minor tweaks on the air screws, and the bike was starting to run worse and worse. Felt like it wasn't sparking / igniting properly - bogging down really badly. Eventually the electronics died completely and the bike wouldn't even bump start.

I got a buddy with a truck to get me and the bike home. Checked the plugs and they all look like this:



looks ok to me. What do you guys think?


It seems to me like the bike isn't charging properly. It has a new battery, but it was not 100% charged when I started the ride. I figured riding it a bit would get it to full juice.

is there any chance that the battery just didn't have enough juice even though it started up quickly on the starter motor? I was turning the bike on and off a lot while I tuned, but I didn't think it would kill it that quickly.


The other issue I have is this on the negative battery lead:




Is that corrosion enough to stop the battery charging?

What'y my best plan forward? How do I diagnose the charging system?

[el pachuco]

spark plug and battery lead both look fine to me.
If you have a voltmeter, check the batteries power. It should have somewhere around 12 volts. If it doesn't your charging system is likely not putting out.

How long was your ride and how many stops and starts did you do in that time?

[riffman12]

ok I'm going to get a volt meter tomorrow. When do I check the battery voltage? At idle? I've heard the system doesn't charge until 2000 rpm or so.

I'd say i only did 5-10 mins of actual riding. With about 6 or 7 stops. I would turn off the ignition at each stop.

[70CB750]

Measure the battery first, it should be about 12.7V or little bit less - if it's charging.

[b52bombardier1]

Recharge the battery and get the bike started again. With your multimeter set for DC volts, check the voltage at the battery at half throttle.  Hope for around 14.5 vdc there.

Flip the multimeter knob to AC volts and see if your rectifier is leaking much AC to the battery. Hope for less than a half a volt AC there. Anything much more indicates a blown or leaky diode in the rectifier.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[calj737]

Perform the tests recommended above. But before you consign a part to "failure", your wiring needs to be double-checked. That battery ground needs to be clean, and it needs to be pinched between the motor mount and the frame, both being clean, bare metal. If your frame is painted and the ground is passing through it, you will get less charge to the battery.

You also need to perform a thorough maintenance of ALL the plugs/connectors, especially those under the left side engine cover coming from the alternator. Is your harness and all charging components stock? If not, revisit how they're connected.

[flybox1]

Your bike may have battery/charging issues to sort out, but if your plugs looked like that after a ride, they're too lean.
What is your current jet setup/mixture screw setting?  whats in your airbox?

As mentioned, perform the charging system tests..

[ekpent]

 Just an observation but those plugs look kind of 'gassy' like they were not getting spark. Might of been from restart attempts. Easy to check for spark with the plugs out by laying on the valve cover and turning over engine. Some danger there though if cylinders have a lot of gas in them   

[CB650CPastor]

With only a 5 to 10 minute ride and shutting the bike off 7 times during that short time/distance, I think we should reserve judgement on reading the plugs to determine anything.

[riffman12]

Measure the battery first, it should be about 12.7V or little bit less - if it's charging.

OK. do this at idle?

Recharge the battery and get the bike started again. With your multimeter set for DC volts, check the voltage at the battery at half throttle.  Hope for around 14.5 vdc there.

Flip the multimeter knob to AC volts and see if your rectifier is leaking much AC to the battery. Hope for less than a half a volt AC there. Anything much more indicates a blown or leaky diode in the rectifier.

Rick

With the meter on AC, I'm still measuring across the battery, right?

Perform the tests recommended above. But before you consign a part to "failure", your wiring needs to be double-checked. That battery ground needs to be clean, and it needs to be pinched between the motor mount and the frame, both being clean, bare metal. If your frame is painted and the ground is passing through it, you will get less charge to the battery.

You also need to perform a thorough maintenance of ALL the plugs/connectors, especially those under the left side engine cover coming from the alternator. Is your harness and all charging components stock? If not, revisit how they're connected.

OK I'll start by cleaning that negative terminal. The other end of it on the frame mount looks very clean - stock.

My harness is stock. I did some rewiring in the headlight and the junction box. Most of the bullet connectors are original, but look to be in good shape.

Your bike may have battery/charging issues to sort out, but if your plugs looked like that after a ride, they're too lean.
What is your current jet setup/mixture screw setting?  whats in your airbox?

As mentioned, perform the charging system tests..

Hm ok so you think the plugs look lean? Here's my specs:

'76 CB750F
Carpy 4 into 1 exhaust with baffle
stock airbox with K&N filter
115 main jets (up from 105)
42 pilots (stock)
haven't touched needle clip

I started with the air screws 1 turn out, which I believe is stock. Then to richen it up a bit I went 1/8 in, then 1/4 in and tweaked back and fourth in that range before the electrics shut down and I lost spark.

Does that sounds reasonable for my setup? Am I way off with my air screws?

I'll be testing charging system tonight

Just an observation but those plugs look kind of 'gassy' like they were not getting spark. Might of been from restart attempts. Easy to check for spark with the plugs out by laying on the valve cover and turning over engine. Some danger there though if cylinders have a lot of gas in them 

I guess there's a good chance they are gassy as I was trying to start the engine (kick and bump start) with a dead electrical system.

[flybox1]

sort your charging system first
Battery at rest should be close to 12.8v

Engine RPM   Battery Terminal Voltage
Idle               12.0v
2000      12.4v
3000      13.2v
4000+      14.5v

[riffman12]

ok cool. I'm going to try that tonight then I'll report back. Thanks again guys!

[Bankerdanny]

Points or electronic ignition?

When I first got my prior 550 on the road in 2011 I experienced something similar to you. In my case the wire that connected the condenser to the points was loose. The result was an intermittent short and only running on 2 cylinders.

A failing condenser causes all sorts of problems including bogging and subsequent fouled plugs.

[riffman12]

the bike has electronic ignition installed by the previous owner. Not sure what brand it is. Looks like this:




interesting point though. As I didn't install the ignition, I don't know it was done properly. Any chance something there could be causing my issue? Are they adjustable or anything?

got my volt meter at lunch and will be testing after work today.

[Jerry Rxman Griffin aka MuthaF'er]

+1 on the main ground. Be SURE the metal it grounds to is clean also.

Stock pilots should have been 40's but that shouldn't affect your voltage and as long as the mixture is correct with your screws it's not a problem.

Check the system voltage coming into and out of your ignition switch.

[riffman12]

ok I did a charging test. Here are my numbers. Battery was charged to 80-90% before this test

Battery by its self = 12.44 V

1000 rpm = 12.07 V

2000 rpm = 12.75 V

3000 rpm = 13.10 V

4000 rpm = 13.00 V

on A/C, I showed 0.01 V at idle

As I did the test more and more the numbers got lower as the battery lost juice.

So all my numbers look OK up until 4k rpm... kinda weird. I even tried again after wire brushing my negative battery lead. nothing changed.

As for the main ground, it is 100% factory - I haven't touched it. Looks really clean.

What do you guys think I should check next? Jerry, you think the started switch could be the issue? I'm terrible with electronics - are there detailed instructions on how to test it?

[b52bombardier1]

This is almost certainly a charging system problem if the battery is new.  Your rectifier is good - not passing much AC.  Could be a regulator problem.   It would be interesting to see what your AC volt levels are coming out of the stator before input to the rectifier.  I would also check the stator coils for continuity and resistance as per the shop manual.

Rick

[Jerry Rxman Griffin aka MuthaF'er]

Lotta juice goes through the ignition switch.

Perhaps charge your battery and have a 'load test' done even though it's basically new. Eliminate a variable. I used Advance Auto Parts. Their tester can test our small batteries.

[riffman12]

This is almost certainly a charging system problem if the battery is new.  Your rectifier is good - not passing much AC.  Could be a regulator problem.   It would be interesting to see what your AC volt levels are coming out of the stator before input to the rectifier.  I would also check the stator coils for continuity and resistance as per the shop manual.

Rick

Ok I'll check this next. Do i have to drain the oil to open up the stator cover? Or is it dry in there?

[calj737]

You don't need to remove the stator cover to check it, just the shift side cover. The stator harness has output plugs beneath there to test.

[flybox1]

ok I did a charging test. Here are my numbers. Battery was charged to 80-90% before this test

Battery by its self = 12.44 V

Charge battery to 100%, remove it from charger.
Wait 2 hours and test voltage at the terminals.  If it reads that low again, its bad.

You should be 14.5v at and above 4000rpm.
Have you gone through all your connectors to clean and inspect?

[riffman12]

ok I did a charging test. Here are my numbers. Battery was charged to 80-90% before this test

Battery by its self = 12.44 V

Charge battery to 100%, remove it from charger.
Wait 2 hours and test voltage at the terminals.  If it reads that low again, its bad.

You should be 14.5v at and above 4000rpm.
Have you gone through all your connectors to clean and inspect?

not yet. That's the plan for tonight. What's a good tool for cleaning the inside of the female bullet connectors? Should I also get some dialectric grease?

The fact that my system is producing some overcharge at 2000 and 3000 rpm, does that mean this might be just a dirty connection / ground issue / bad battery rather than a total non charging issue (stator, regulator etc.)?

Also, is there any chance my system is fine and I just used the electric start too many times with frequent stops? If the bike is idling, should it maintain charge? Or would it die if you left it long enough at 1000rpm?

Thanks again guys. I hate electrics 

[flybox1]

not yet. That's the plan for tonight. What's a good tool for cleaning the inside of the female bullet connectors? Should I also get some dialectric grease?   .22 cal bore brush, or a steel wool q-tip(make one).  dielectric grease is a good thing

The fact that my system is producing some overcharge at 2000 and 3000 rpm, does that mean this might be just a dirty connection / ground issue / bad battery rather than a total non charging issue (stator, regulator etc.)? clean and treat your whole harness to rule it out, first

Also, is there any chance my system is fine and I just used the electric start too many times with frequent stops? If the bike is idling, should it maintain charge?  Or would it die if you left it long enough at 1000rpm? idling at 1000rpm, especially with lights on, is a net loss of voltage

Thanks again guys. I hate electrics 

[b52bombardier1]

I like Caig's DeOxit D5 at Radio Shack. It removes that blue green oxide on bullet connectors that have seen water too long.

Then give the female side a little squeeze to tighten it and you might be ok.

But a word of caution.  This old Honda wiring can look ok at the insulation near the connector but only be hanging on by as little as a single tiny strand of copper internally. It would even test good on a multimeter in this condition but flow very little for amps. Sometimes, an even remotely questionable connector - male or female - should be replaced.  The folks at Vintage Connections make a great kit for this.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[riffman12]

ok so I started digging into the electrical panel this evening and things got more yucky as I went. See for yourself:

Here's the panel its self:




Rectifier:






Regulator looks to be in OK shape:




Scariest part, the connectors coming from the stator and the harness:




The wiring on the rest of the bike is super clean, wires are bendable etc. Just this area under the seat is bad.

So I get the feeling this is where my charging issue is coming from... it looks like a battery popped in the past and spilled acid over everything.

A lot of it comes off pretty easily as nasty dust, not stuck on like rust or anything. Some of the cables are a little brittle, but still bendable.

Do you guys think this is salvageable / cleanable? I have no problem replacing individual components (buying a new rec/reg combo for example), but I'm a little scared of replacing an entire harness. It also seems like it would be a ton of work 

Any thoughts?