Topic: First start attempt - Fail

[RAFster122s]

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750K2A_MOTORCYCLE%2c_JPN%2c_VIN%23_CB750-2000001/POINTS_%2b_SPARK_ADVANCER/78d6b920-62a4-40b9-b85b-e5ab2abab37c/431f2f9e-a95d-45b4-846f-990537e73c6a/y


The complete points plate, item #1 is a better deal…

But, I think you need to verify the condenser is good swapping them. If it is and your voltage comes up or putting the #2 condenser in #1 spot doesn’t exhibit low voltage… then you have a wiring issue to #2 coils…

The voltage should be 12v just like #1 & 4.

You can bypass the original wiring to feed 12v to the #2 coil directly from the battery and the points to see if your bike then fires on 2&3.

Take your wiring diagram and replicate the wiring to the coil and points and you can use alligator clips if that works.
Use a crimped terminal at the points and condenser…

But, voltage & resistance readings should tell you if you have issues from disconnected wiring to isolate it…

The resistance from one point to another on the wiring should be a very low number approaching zero if you are not reading other devices in the circuit.

Wiring diagram for K3
http://manuals.sohc4.net/cb750k/technical_reference/WD750K3_K7.jpg

Yellow wire input to coil 2&3 should read 12v or close to battery voltage with key on and kill switch in run. Same voltage should be seen at Blue wire input to coil 1&4.  Voltage at points plate yellow and blue wires should be seen within 0.1v measured with positive probe and negative probe at battery negative terminal.

Right?

[Mark K]

Swap the condensers and see if the problem follows.  If you have old condensers try swapping that in.

A leaky condenser can become resistive and bleed off voltage as well as prevent spark at  the plugs.

I'll swap the condensers and see if issue follows. I kept all the old components, I'll install old condenser and see if that removes the issue.

Thanks TwoTired.

[Mark K]

  My goodness you've done your due diligence, sorry we haven't helped yet.

I really appreciate everyone's help, advice, suggestions and recommendations. This forum has been immensely helpful to me on this project. I'm sure we will get it figured out, and by we, I mean everyone here helping me!!

[Mark K]

Swap the condensers and see if the problem follows.  If you have old condensers try swapping that in.

A leaky condenser can become resistive and bleed off voltage as well as prevent spark at  the plugs.

Would new/'fresh' condensers still be available ?
Where can I buy fresh condensers with a manufacturers date stamp ?
I remember HondaMan/Mark describing that if an NOS condenser has been on the shelf longer than 5 yrs,it's already 'on it's way out'.

I bought the replacement points/condensers from VintageCB750 in Canada 🇨🇦. Didn't think to look for a stamp on the parts, but the packaging said made in Taiwan.

[Mark K]

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750K2A_MOTORCYCLE%2c_JPN%2c_VIN%23_CB750-2000001/POINTS_%2b_SPARK_ADVANCER/78d6b920-62a4-40b9-b85b-e5ab2abab37c/431f2f9e-a95d-45b4-846f-990537e73c6a/y


The complete points plate, item #1 is a better deal…

But, I think you need to verify the condenser is good swapping them. If it is and your voltage comes up or putting the #2 condenser in #1 spot doesn’t exhibit low voltage… then you have a wiring issue to #2 coils…

The voltage should be 12v just like #1 & 4.

You can bypass the original wiring to feed 12v to the #2 coil directly from the battery and the points to see if your bike then fires on 2&3.

Take your wiring diagram and replicate the wiring to the coil and points and you can use alligator clips if that works.
Use a crimped terminal at the points and condenser…

But, voltage & resistance readings should tell you if you have issues from disconnected wiring to isolate it…

The resistance from one point to another on the wiring should be a very low number approaching zero if you are not reading other devices in the circuit.

Wiring diagram for K3
http://manuals.sohc4.net/cb750k/technical_reference/WD750K3_K7.jpg

Yellow wire input to coil 2&3 should read 12v or close to battery voltage with key on and kill switch in run. Same voltage should be seen at Blue wire input to coil 1&4.  Voltage at points plate yellow and blue wires should be seen within 0.1v measured with positive probe and negative probe at battery negative terminal.

Right?

Thank you for the info/testing suggestions. I've got the wiring diagram printed out large and will start with swapping condensers. If that doesn't fix issue, then I'll check all the items you've suggested. Thanks again.

[grcamna2]

Have a look at your right hand switch,kill switch? the ignition power can be stopped up there.
I've worked on a couple vintage Honda's that had a bad connection/corrosion on the wires or the ground wire/connection to the handlebar switch was isolated by rubber mounts on the handlebars,etc. which didn't complete the circuit. The switches/bars need a ground connection.

[Mark K]

Swap the condensers and see if the problem follows.  If you have old condensers try swapping that in.

A leaky condenser can become resistive and bleed off voltage as well as prevent spark at  the plugs.

Swapped the condensers, the 10.7 did NOT follow. I checked voltage in the yellow / blue wires (next to brake light switch) and yellow was 10.7v, blue was 12.0v. Checked the yellow / blue wires at the coil, same thing, yellow 10.7v, blue was 12.0v. Hooked old 1/4 coil in place of new 2/3 coil (old coil had good spark before). Yellow now reading 12.0v. Tested voltage at points, reading 11.8. Should've checked the voltage output earlier, but figured new coils would be good - my mistake. So I think the low voltage issue is identified and I can swap out an old coil for new for now.

A new problem has arrived, new 2/3 points will not fully close so I'm getting voltage when they're open and when they're supposed to be closed. If I push them closed, voltage drops to zero as it should. These points have only been on for a few days and the bike isn't running yet, so what the heck?? I set the points per the FSM the other day and double checked the static setting today. What could cause the points to not fully close?

[Mark K]

Have a look at your right hand switch,kill switch? the ignition power can be stopped up there.
I've worked on a couple vintage Honda's that had a bad connection/corrosion on the wires or the ground wire/connection to the handlebar switch was isolated by rubber mounts on the handlebars,etc. which didn't complete the circuit. The switches/bars need a ground connection.

Checked the right hand kill switch, voltage to points when kill switch is in run, no voltage at points when switch is either kill position. Thanks for the suggestion.

[newday777]

Swap the condensers and see if the problem follows.  If you have old condensers try swapping that in.

A leaky condenser can become resistive and bleed off voltage as well as prevent spark at  the plugs.

Would new/'fresh' condensers still be available ?
Where can I buy fresh condensers with a manufacturers date stamp ?
I remember HondaMan/Mark describing that if an NOS condenser has been on the shelf longer than 5 yrs,it's already 'on it's way out'.

I bought the replacement points/condensers from VintageCB750 in Canada 🇨🇦. Didn't think to look for a stamp on the parts, but the packaging said made in Taiwan.

You bought aftermarket points and condensers. Most likely the problem lies here. If they don't have the 'TEC' or Toyo brand mark on them they aren't going to be reliable.
This is one place not to try to skimp on cost when staying with points and condensers. Buy them only from Honda.

[newday777]

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750K2A_MOTORCYCLE%2c_JPN%2c_VIN%23_CB750-2000001/POINTS_%2b_SPARK_ADVANCER/78d6b920-62a4-40b9-b85b-e5ab2abab37c/431f2f9e-a95d-45b4-846f-990537e73c6a/y


The complete points plate, item #1 is a better deal…

But, I think you need to verify the condenser is good swapping them. If it is and your voltage comes up or putting the #2 condenser in #1 spot doesn’t exhibit low voltage… then you have a wiring issue to #2 coils…

The voltage should be 12v just like #1 & 4.

You can bypass the original wiring to feed 12v to the #2 coil directly from the battery and the points to see if your bike then fires on 2&3.

Take your wiring diagram and replicate the wiring to the coil and points and you can use alligator clips if that works.
Use a crimped terminal at the points and condenser…

But, voltage & resistance readings should tell you if you have issues from disconnected wiring to isolate it…

The resistance from one point to another on the wiring should be a very low number approaching zero if you are not reading other devices in the circuit.

Wiring diagram for K3
http://manuals.sohc4.net/cb750k/technical_reference/WD750K3_K7.jpg

Yellow wire input to coil 2&3 should read 12v or close to battery voltage with key on and kill switch in run. Same voltage should be seen at Blue wire input to coil 1&4.  Voltage at points plate yellow and blue wires should be seen within 0.1v measured with positive probe and negative probe at battery negative terminal.

Right?

As RAF said at the top of this page, Southsound is the place to buy them. Buying the points and condensers individually(#3, 4, & #10-x2 )will cost more then buying the whole assembly (#1)

[Mark K]

Newday, thanks for the information and reminder about the info RAF posted. I've looked at the website, have it saved and will purchase in the near future.

[Stev-o]

I bought the replacement points/condensers from VintageCB750 in Canada 🇨🇦. Didn't think to look for a stamp on the parts, but the packaging said made in Taiwan.

Hey Mark...this may be a clue, you could have faulty parts.

[Mark K]

Hey Mark...this may be a clue, you could have faulty parts.

Stev-o, if I didn't know better, I'd almost think you were being facetious 😂

Yeah, definitely faulty parts.

[Mark K]

Replaced new 2/3 coil with old 1/4 coil (it worked before, voltage and spark). Removed new points & condensers, replaced with old points. Removed all 4 carb bowls, checked the floats, everything looked like it was supposed to, put bowls back on. Labeled drain tubes, so I can see which ones leak, if any. Hooked up fuel test tank, slaved bike battery to truck and finally, FINALLY got it to run. Tried to set idle, got it close. I'll try to upload a video. Now I need to buy carb synchronizers.

Suggestions on what carb synchronizer to buy?

Thanks again for everyone's help!

[grcamna2]

Replaced new 2/3 coil with old 1/4 coil (it worked before, voltage and spark). Removed new points & condensers, replaced with old points. Removed all 4 carb bowls, checked the floats, everything looked like it was supposed to, put bowls back on. Labeled drain tubes, so I can see which ones leak, if any. Hooked up fuel test tank, slaved bike battery to truck and finally, FINALLY got it to run. Tried to set idle, got it close. I'll try to upload a video. Now I need to buy carb synchronizers.

Suggestions on what carb synchronizer to buy?

Thanks again for everyone's help!

Nice    I recommend analog gauges;there are a few quality sets of them available.
The ones with adjustable dampeners for each individual gauge are a great feature.

Send a PM to member here 'dave500' and let him post a picture or two of his gauges 

[Mark K]

Thanks, I'll do that.

[Mark K]

Ten second video here -

[denward17]

So you had bad new points/condensers ?

[PeWe]

Sure the connector on point is not shorted to its ground?

Easy that it can happen with those fork type of connector.

I used the Daichii back in the 80's. They worked but trickier to adjust 2:3.

[RAFster122s]

Possibly bad coil for 2/3 as well.
Glad you got it running better.

Sync gauges need restrictors or aquariums bleed valves to eliminate the pulsing that messes with STD vac gauges commonly sold. MotionPro and Gunson gauges don't have that issue as they designed theirs to compensate...
FWIW

Fluid type gauges ya gotta be careful with as a few have had motor suck the fluid in when not setup correctly and then you have to buy new fluid... Oops.

David

[Mark K]

So you had bad new points/condensers ?

Yeah, it seems the 2/3 points were wonky or something. They initially worked (static setting and then checking for voltage/no voltage when they were open/closed). After a day of sitting, 2/3 would not fully close. I don't get it, but in the future I will stick with name brand parts, as the experts here recommend/suggest.

Also, the brand new 2/3 coil was bad, I was only getting 10.7v from it, when 1/4 was slightly over 12v.

[Mark K]

Sure the connector on point is not shorted to its ground?

Easy that it can happen with those fork type of connector.

I used the Daichii back in the 80's. They worked but trickier to adjust 2:3.

Thanks PeWe, I double-checked the point connectors, made sure the fork connectors was flat.

[Mark K]

Possibly bad coil for 2/3 as well.
Glad you got it running better.

Sync gauges need restrictors or aquariums bleed valves to eliminate the pulsing that messes with STD vac gauges commonly sold. MotionPro and Gunson gauges don't have that issue as they designed theirs to compensate...
FWIW

Fluid type gauges ya gotta be careful with as a few have had motor suck the fluid in when not setup correctly and then you have to buy new fluid... Oops.

David

Thanks David, good info to have when shopping for guages.

[Stev-o]

Good to see you have it running, it sounds healthy.

I have a spare set of Honda sync gauges if that interests you?

[Mark K]

Good to see you have it running, it sounds healthy.

I have a spare set of Honda sync gauges if that interests you?

I'll PM you Stev-o.