Topic: 11 Volts at the Coils

[pjandrew99]

Bike is running poorly. Did 3000 mile tune up with no change. Installed new Honda point assembly. Looking at spark. Seems weak visually but may be acceptable.
Primary, secondary and cap numbers look good. My concern is the voltage drop from 13.05 battery to 11.04 and 11.03 at the coils. Can I get a workable spark at 11 volts? I'm thinking carbs are the culprit at this point but starting the beast has become more difficult as well.

CB750K1
Aftermarket coils

[TwoTired]

If I understand you correctly, you are saying that your distribution of power from battery to coil input is losing 2 volts. That is a problem with wires, connectors, fuse clips, and or switch contacts In your electrical distribution system .  It could be a single component or a cumulative loss from multiple components.

I would verify your diagnosis by turning on all electrical loads and putting voltmeter probes on battery POS and input to coil. The meter will show you the loss in that path.  Do the same test but with probes on battery NEG and either the points plate or blue or yellow wires with the point contact closed.  Check meter calibration on lowest scale and note reading with probe tips touched together.  Subtract that reading from all your measurements.

If the sum of both above measurements verifies voltage loss,  then you need clean all the connections in the wire harness, fuse clips and switch contacts.

After you verify that your wiring is

[pjandrew99]

If I understand you correctly, you are saying that your distribution of power from battery to coil input is losing 2 volts. That is a problem with wires, connectors, fuse clips, and or switch contacts In your electrical distribution system .  It could be a single component or a cumulative loss from multiple components.

I would verify your diagnosis by turning on all electrical loads and putting voltmeter probes on battery POS and input to coil. The meter will show you the loss in that path.  Do the same test but with probes on battery NEG and either the points plate or blue or yellow wires with the point contact closed.  Check meter calibration on lowest scale and note reading with probe tips touched together.  Subtract that reading from all your measurements.

If the sum of both above measurements verifies voltage loss,  then you need clean all the connections in the wire harness, fuse clips and switch contacts.

After you verify that your wiring is

Thank you. I will do that. Much appreciated.

[Don R]

 I'm curious what the lowest observed voltage loss is on one of these bikes.

[bryanj]

Could also be a tired battery

[PeWe]

Ignition and lamps on affect the voltage when engine is not running.

[pjandrew99]

Could also be a tired battery

battery is relatively new.

Ignition and lamps on affect the voltage when engine is not running.

So would 11 volts at the coils be a typical reading when the ignition and lamps are on? I went from 13v battery to 11v coils with ignition and lamp on. I'm thinking my spark is weak because it visually looks that way. However, it may be totally acceptable. Just trying to rule out potential issues before diving into the carbs.

[Scootch]

Just for grins I would check the resistance of the wiring path from battery to coils. I can't offer a number regarding what a ohms number you should expect but I would want it to be low resistance. Probably shouldn't be more than an ohm or two. Look at wires and connectors for issues. Also maybe check resistance of coil primaries and secondaries to see if the resistance values are where they should be. I would disconnect the coils from the rest of the circuit when you attempt to measure otherwise you could get outside circuit influence.

[PeWe]

I should check the voltages at different rpms with light on and off according to the CB750 Shop manual ch.8.
Battery must be fully charged before test.

Clean all connectors and make sure that ground connections are metal against metal.
Battery ground cable to left upper engine bolt. No paint under (frame-frame- engine) vaseline work as corrosion protection.

Same for ground to frame beside seat locking device.

Then check again and see the difference.

[pjandrew99]

Yep, time to go through all the connections. Thanks to all!!!

[Deltarider]

Yep, time to go through all the connections. Thanks to all!!!

Could be a waste of time. Simply measure the V-drop between BATT + and COILS + with the engine running at various RPM. Battery needs to be in good condition and well charged. Like Bryanj said: a tired battery is not a good starting point.
A measured 11V at the coils with just IGN ON is not unusual.

[pjandrew99]

Yep, time to go through all the connections. Thanks to all!!!

Could be a waste of time. Simply measure the V-drop between BATT + and COILS + with the engine running at various RPM. Battery needs to be in good condition and well charged. Like Bryanj said: a tired battery is not a good starting point.
A measured 11V at the coils with just IGN ON is not unusual.

Got a better multimeter. Getting 11.48 volts at each coil.  Ignition on, not running. Once I get it running I will certainly check at various rpm's.  I've got the time so I'll go over the connections but I think the running issue is pointing to the carbs.

[pjandrew99]

Ps. I'm also curious to see if there is an increase in the voltage after cleaning all the connections.

[HondaMan]

I also treat(ed) the connectors with LPS-1 (hard stuff to find, and is NOT like their LPS2 or 2.5, or LPS-3) as it was developed expressly for the metals used in these older bikes' wiring. The plugs are zinc-plated steel: steel because it was cheap and zinc to prevent rust for 10 years of anticipated life. Now 5 times those years later, the zinc is flaking off and the steel is corroding. The LPS-1 stops both and also seals out air, but lets the metal-to-metal contact be completely uninhibited. Cool stuff, really.

Back in the 1980s I made Command-Control systems for model train hobbyists. These had little receiver boards in the locomotives and used RC circuit channels to allow the User to select 1 of 63 locomotives on a layout and control it with his handheld throttle. The only fly in this otherwise very cool ointment was the train tracks: they got dirty and cruddy and often made poor contact, interrupting both power and command to the train. Putting a drop of LPS-1 on each rail, about every 10 feet of track or so, stopped the corrosion and signal interruption completely, and only needed to be done once every few years in that open-air environment. LPS-1 was developed to also withstand salt water spraying (it came from Naval electrical gear), so in these bike's electrics it only needs to be done once to last for decades. I think I did mine in 1995-ish, never had any more issues.

[Deltarider]

Got a better multimeter. Getting 11.48 volts at each coil.  Ignition on, not running.

That's certainly good enough. Me, I'd leave the connectors alone unless V-drop measurement indicates there's a problem. The only electric problem I had, was the IGN key switch (replaced by an aftermarket one from CMSNL) and I have had to clean the fuses and their clamps. Connectors that needed cleaning? None so far. Cleaning them in the blind, without a diagnosis, is not for me.

[newday777]

I also treat(ed) the connectors with LPS-1 (hard stuff to find, and is NOT like their LPS2 or 2.5, or LPS-3) as it was developed expressly for the metals used in these older bikes' wiring. The plugs are zinc-plated steel: steel because it was cheap and zinc to prevent rust for 10 years of anticipated life. Now 5 times those years later, the zinc is flaking off and the steel is corroding. The LPS-1 stops both and also seals out air, but lets the metal-to-metal contact be completely uninhibited. Cool stuff, really.

Back in the 1980s I made Command-Control systems for model train hobbyists. These had little receiver boards in the locomotives and used RC circuit channels to allow the User to select 1 of 63 locomotives on a layout and control it with his handheld throttle. The only fly in this otherwise very cool ointment was the train tracks: they got dirty and cruddy and often made poor contact, interrupting both power and command to the train. Putting a drop of LPS-1 on each rail, about every 10 feet of track or so, stopped the corrosion and signal interruption completely, and only needed to be done once every few years in that open-air environment. LPS-1 was developed to also withstand salt water spraying (it came from Naval electrical gear), so in these bike's electrics it only needs to be done once to last for decades. I think I did mine in 1995-ish, never had any more issues.

Is this it Mark?

LPS NO.1 Lubricant 11OZ by LPS MfrPartNo 00116 https://a.co/d/bkHIpqD

[HondaMan]

I also treat(ed) the connectors with LPS-1 (hard stuff to find, and is NOT like their LPS2 or 2.5, or LPS-3) as it was developed expressly for the metals used in these older bikes' wiring. The plugs are zinc-plated steel: steel because it was cheap and zinc to prevent rust for 10 years of anticipated life. Now 5 times those years later, the zinc is flaking off and the steel is corroding. The LPS-1 stops both and also seals out air, but lets the metal-to-metal contact be completely uninhibited. Cool stuff, really.

Back in the 1980s I made Command-Control systems for model train hobbyists. These had little receiver boards in the locomotives and used RC circuit channels to allow the User to select 1 of 63 locomotives on a layout and control it with his handheld throttle. The only fly in this otherwise very cool ointment was the train tracks: they got dirty and cruddy and often made poor contact, interrupting both power and command to the train. Putting a drop of LPS-1 on each rail, about every 10 feet of track or so, stopped the corrosion and signal interruption completely, and only needed to be done once every few years in that open-air environment. LPS-1 was developed to also withstand salt water spraying (it came from Naval electrical gear), so in these bike's electrics it only needs to be done once to last for decades. I think I did mine in 1995-ish, never had any more issues.

Is this it Mark?

LPS NO.1 Lubricant 11OZ by LPS MfrPartNo 00116 https://a.co/d/bkHIpqD

Yes, only that can is a LIFETIME supply! It takes only a drop for each connector. I spray a dribble into the cap and use a cotton swab or toothpick to apply it. The LPS company makes little 1-ounce cans, too, which I used to sell with the model train electronics long ago, as one ounce would do a typical train layout for 10 years or more. I've seen it lately in those little cans online somewhere, but I can't remember who had it: I think it might be MSC Supply or one of those industrial supply stores? I called it the "purse size" can.

[newday777]

Thanks Mark 

[pjandrew99]

I also treat(ed) the connectors with LPS-1 (hard stuff to find, and is NOT like their LPS2 or 2.5, or LPS-3) as it was developed expressly for the metals used in these older bikes' wiring. The plugs are zinc-plated steel: steel because it was cheap and zinc to prevent rust for 10 years of anticipated life. Now 5 times those years later, the zinc is flaking off and the steel is corroding. The LPS-1 stops both and also seals out air, but lets the metal-to-metal contact be completely uninhibited. Cool stuff, really.

Back in the 1980s I made Command-Control systems for model train hobbyists. These had little receiver boards in the locomotives and used RC circuit channels to allow the User to select 1 of 63 locomotives on a layout and control it with his handheld throttle. The only fly in this otherwise very cool ointment was the train tracks: they got dirty and cruddy and often made poor contact, interrupting both power and command to the train. Putting a drop of LPS-1 on each rail, about every 10 feet of track or so, stopped the corrosion and signal interruption completely, and only needed to be done once every few years in that open-air environment. LPS-1 was developed to also withstand salt water spraying (it came from Naval electrical gear), so in these bike's electrics it only needs to be done once to last for decades. I think I did mine in 1995-ish, never had any more issues.

Is this it Mark?

LPS NO.1 Lubricant 11OZ by LPS MfrPartNo 00116 https://a.co/d/bkHIpqD

Yes, only that can is a LIFETIME supply! It takes only a drop for each connector. I spray a dribble into the cap and use a cotton swab or toothpick to apply it. The LPS company makes little 1-ounce cans, too, which I used to sell with the model train electronics long ago, as one ounce would do a typical train layout for 10 years or more. I've seen it lately in those little cans online somewhere, but I can't remember who had it: I think it might be MSC Supply or one of those industrial supply stores? I called it the "purse size" can.

Great info! I'm wondering how it would compare to silicone or dielectric grease. Have those sitting on the shelf.