Topic: 1974 CB750, new bike, new owner, new user, and new questions :P

[piefairy]

The petcock on the bike isn't original, at-least according to DCC and every other site I've check. The tank also isn't original from what I can tell since the badges are adhesive and not screw on. Didn't realize all this until after I drained the tank and pulled it this afternoon. I'm guessing the tank is a replacement, or there were different versions if it is stock. I'm just trying to figure it all out and since the sites I've found point to a different type of petcock attachment, I'm trying to find out exactly what I am dealing with.

[piefairy]

So the tank is a later production, that makes sense. Probably why the badges are adhesive. I have checked both the engine and the vin both date to 64.

[piefairy]

The petcock that came with the bike is missing the tube that I assume alerts you to low fuel and you switch to reserve. Is this something I can replaced? Or anyone know a jerry rig that can be used?

[piefairy]

Can someone ID this part? Its the lock washer that goes inside the clutch assembly, but I dont know the name so I can order a replacement.

[calj737]

https://www.cmsnl.com/honda-cb750k4-four-1974-usa_model482/partslist/

[piefairy]

Thanks!

[piefairy]

Anyone know where its available in the US?

[754]

Yes your tank is 75 or 76, my 74 has the same thing.
 Bad because those are the wurst petcocks,  and if your bike is 74 like mine its harder to adjust the main idle screw.
 It's a pain if you break a throttle cable and you play with the idle adjustvto get-r-home.

[calj737]

Anyone know where its available in the US?

Find the part number on the fiche, then Google that part number. It’s a lot easier than you think.

[piefairy]

Alright, I've started wiring in my M-unit blue. Cal, I may test your patience  I am using 2 sets of m-switch mini's. I know that interference is an issue with these. I am using stock bars, but does it need to be run through the frame back to the m unit or just the bars? Has anyone tried using a copper mesh cage to block the noise?

I've got it turning over the starter with the semi-stock factory wiring. I am hoping to bypass the clutch and kickstand sensors and just have the neutral sensor in place. I've done that with jumper wires, but I am curious if at this point I can drop the entire starter safety unit. I would like a neutral light indicator, and have it keep the starter from turning over, but that is it. Is this possible? Or should I just keep the safety unit and jumper the unwanted?

Next bit would be the speedo. I do have a connection on the front fork that is wired into the speedo, but I am not sure if it would put out a signal the M-unit can understand. I am looking to use the motomini speedo. Can I use the Acewell digital speedo cable adapter to work with the m unit?
https://www.dimecitycycles.com/acewell-digital-speedometer-conversion-cable-for-honda-crf-yamah-wr-ktm.html

The only idiot lights I am looking to have are neutral, turn signal, and high beam. Am I safe to wire these inline from the output of the M unit? I will diode the turn signals to prevent it from triggering both lights.

Last question at the moment. Should I wire in a full kill/disconnect switch to save battery if its going to sit a while? Even though the draw is very low, is it a good idea?

Thanks!

Also, I noticed one of the Comp Condensers (?) is dented from what looks to be a drop in the past. I assume I should go ahead and replace it correct?

[calj737]

Alright, I've started wiring in my M-unit blue. Cal, I may test your patience  I am using 2 sets of m-switch mini's. I know that interference is an issue with these. I am using stock bars, but does it need to be run through the frame back to the m unit or just the bars? Has anyone tried using a copper mesh cage to block the noise?

I've got it turning over the starter with the semi-stock factory wiring. I am hoping to bypass the clutch and kickstand sensors and just have the neutral sensor in place. I've done that with jumper wires, but I am curious if at this point I can drop the entire starter safety unit. I would like a neutral light indicator, and have it keep the starter from turning over, but that is it. Is this possible? Or should I just keep the safety unit and jumper the unwanted?

Next bit would be the speedo. I do have a connection on the front fork that is wired into the speedo, but I am not sure if it would put out a signal the M-unit can understand. I am looking to use the motomini speedo. Can I use the Acewell digital speedo cable adapter to work with the m unit?
https://www.dimecitycycles.com/acewell-digital-speedometer-conversion-cable-for-honda-crf-yamah-wr-ktm.html

The only idiot lights I am looking to have are neutral, turn signal, and high beam. Am I safe to wire these inline from the output of the M unit? I will diode the turn signals to prevent it from triggering both lights.

Last question at the moment. Should I wire in a full kill/disconnect switch to save battery if its going to sit a while? Even though the draw is very low, is it a good idea?

Thanks!

Also, I noticed one of the Comp Condensers (?) is dented from what looks to be a drop in the past. I assume I should go ahead and replace it correct?

Dude, you're all over the place! 

I am unaware of any "interference" with the M-switches. Only thing that causes a problem is the M-Button, which must be run through metal bars (inside) to prevent conflicts. The M-switches are nothing more than momentary grounds to switch voltage at the M-Unit.

It is far easier to ditch ALL the stock wiring, and run all new looms from the M-Unit and the M-switches. Far easier.

Your idiot lights get powered from the M-unit. The NEU and OIL (you WANT OIL TOO) are powered by AUX, the "-" side of that light comes from the NEU and OIL switch directly.

TURNs and HI come from the M-Unit outputs for those respectively. You simply tap into the front lead for TURN L, R and HI. The inputs for these go the Moto-Mini. The Mini has a speedo input sensor with it. The "tach" is wired to the coils.

You don't need a diode for your TURNs as the Moto Mini should have separate inputs for L and R.

Digest this and let's start again-

[piefairy]

Thanks for the input. I am making a new wiring loom. The old one was all kinds of funky. I have the Motogadget wiring kit, so I will be using their color codes in the new lines.

 The reason I was thinking I would need to diode the turn signal indicator is that there will be only 1 LED, and it would be wired in-line to the front LED turn signals so it would without a diode, wouldn't the signal flow to both blinkers regardless of which one is intended to be on?

I had left off the oil pressure light because I had read on another site that the sensors tended to fail and that it should be replaced with an analog gauge drilled and taped to the motor. If this isn't true, I would much rather the idiot light than risking hurting the engine.

As for the speedo input, does the stock cable from the bike put out a usable signal? I always had it in my head that the speedo was a physically moving part, but now that I think about it, its not actually touching the wheel to move... so I guess it is a pickup...

Also, since I am using all LED lights, am I safe to ground them at the installation site to the frame rather than running a - all the way back to the battery? I have my m-unit getting its - from the mounting holes for it as well. I am running the M-switches back to M-unit to ground them though.

Thanks again!

[calj737]

Thanks for the input. I am making a new wiring loom. The old one was all kinds of funky. I have the Motogadget wiring kit, so I will be using their color codes in the new lines.

I’d encourage you to retain the stock colors as much as possible. It will make troubleshooting for you, and anyone else far easier.

The reason I was thinking I would need to diode the turn signal indicator is that there will be only 1 LED, and it would be wired in-line to the front LED turn signals so it would without a diode, wouldn't the signal flow to both blinkers regardless of which one is intended to be on?

I had left off the oil pressure light because I had read on another site that the sensors tended to fail and that it should be replaced with an analog gauge drilled and taped to the motor. If this isn't true, I would much rather the idiot light than risking hurting the engine.

If your gauge does not have the idiot light inputs and you are using a single aftermarket LED, then yes, you’ll need inline diodes.

As for the speedo input, does the stock cable from the bike put out a usable signal? I always had it in my head that the speedo was a physically moving part, but now that I think about it, its not actually touching the wheel to move... so I guess it is a pickup...

No, the MotoG gauge is looking for an electronic signal from its magnetic sensor (Hall type). The stock is mechanical.

Also, since I am using all LED lights, am I safe to ground them at the installation site to the frame rather than running a - all the way back to the battery? I have my m-unit getting its - from the mounting holes for it as well. I am running the M-switches back to M-unit to ground them though.

You can ground your idiot lights (Turns and HI) locally. The OIL and NEU are supplied a ground form the respective switch already. And the stock OIL switch is plenty reliable. Folks use the auxiliary pressure gauge to know how much pressure the engine is seeing.

The switches must be wired to the input side of the gauge to activate the function.

[piefairy]

As for the speedo input, does the stock cable from the bike put out a usable signal? I always had it in my head that the speedo was a physically moving part, but now that I think about it, its not actually touching the wheel to move... so I guess it is a pickup...

No, the MotoG gauge is looking for an electronic signal from its magnetic sensor (Hall type). The stock is mechanical.

If the speedo is mechanical will the adapter in my previous post work or do I need to go through the process of completely changing it? My M-unit kit came with the magnets but no pickup.

And yes, I will be using independent LEDs, the speedo I will be using does not have inputs for idiot lights.

I will keep the stock wiring colors as best as possible then.

[calj737]

The magnet gets installed opposite a metal “bolt”. You can use a bolt on the front sprocket, anywhere on the wheel, or any other object that rotates at the speed of the motorcycle.

Use the supplied magnetic sensor for the MotoG Mini.

[piefairy]

The magnet gets installed opposite a metal “bolt”. You can use a bolt on the front sprocket, anywhere on the wheel, or any other object that rotates at the speed of the motorcycle.

Use the supplied magnetic sensor for the MotoG Mini.

Got it, thanks!

It will be a day or two before I get back at it on the bike for the wiring atleast, waiting on a few parts. I'm sure I will bug you again when I get back to it 

[piefairy]

Ok Cal, here is the next bit. I'm starting on the harness. I believe I have this wired correctly. The starter kicks over, but the carbs are off and I haven't wired a kill yet so I cant see if it runs yet. I've attached a photo. There are 4 lines on ricks reg I'm not sure what to do with. I believe 3 are not needed, and the fourth is green I assume its ground? The three I dont think are needed are White, Yellow, Green, not the ones on the molex connector

I have attached an attempt at a wiring diagram. Hopefully it is usable. I was limited to Microsoft Publisher, so its not great. Also, the M unit and the battery are grounded to the frame, just didn't draw it.

Also, I put a 15A fuse to the M unit... but I am thinking that should have gone between the battery and the starter relay. What value fuse should I place on the M unit?

<a href='https://postimg.cc/image/j4rrodqz1/' target='_blank'><img src='https://s14.postimg.cc/j4rrodqz1/wiring_1-0.jpg' border='0' alt='wiring_1-0'/>[/url]

[calj737]

All 7 wires from the Ricks are needed for the charging system to function properly.
3 yellows go to stator, white goes to fuel coil, red to battery POS, and greens to ground and the black to the LOCK port please.

[mrbreeze]

I didn't see if you got straightened out on the petcock situation but I can explain it to you. All K's up to 1974 had the petcock on the right side that is mounted to tank with 2 screws. It has a small strainer screen in the bottom that unscrews from the body of the petcock. 75-76 K's moved the petcock to the left side of the tank and mount on a threaded bung. The filter is a net that covers the pipes up into the tank that supply the fuel. The tanks are interchangeable but you must reroute the fuel line(s) to the carbs.

[piefairy]

Sorry, its been a few days since I got to post. I've been waiting on parts and just doing minor things as well as starting to strip the un-wanted parts.

The petcock was figured out, the tank on my bike was a 76 or so, not the 74 like the bike. Thanks for following up though.

What color wire is the fuel coil? I don't see anything by that name in on my stock wiring schematic.

Which lock port do you mean for the black? The LOCK on the M-unit or the key-ignition switch assembly? I have removed the key assembly on the bike. I am planning to use a relayed kill switch to disable the entire POS from the battery and the M-unit.

Also, I didn't hear on the 15A fuse. Should that be between the battery POS and starter or to the M-unit? I'm thinking the starter, but want to make sure. Also, what value fuse should I use to the M-unit, just in case? I know its internally fused, but still.

I pulled the neutral switch and it seems that the PO was having an oil leak issue and decided to glue it in. All that came out were the internals. Any suggestions on how I could remove the outer casing? I attached a photo of what came out.



One last question for the day. I got my new clutch kit in. It came with 6 metal plates and 8 friction disks. I know the large tanged friction disk goes on the outside, but I have some questions on the number of friction disks I need to use. I do not have the double pressure plate version of the clutch, so I would assume I would need all 8 disks, but I am not sure of how this would be arranged. The clutch I pulled out only has 7 disks and 6 plates, but that would be the setup for the double plate version correct? If I need all 8 disks, I feel like I am missing a pressure plate. Thoughts?

The bikes clutch was either "disengaged or engaged" which is why I thought the plates were worn, but if the assembly was incorrect and a disk or plate were missing, it would make sense for this to be the case, correct?

[piefairy]

Just for reference, this is the kit I ordered. I ordered the friction plates, disks, and springs.

http://www.barnettclutches.com/344/honda/0/0/1974-honda-cb750k-f.html

[calj737]

What color wire is the fuel coil? I don't see anything by that name in on my stock wiring schematic.
Typo on my part, FIELD COIL

Which lock port do you mean for the black? The LOCK on the M-unit or the key-ignition switch assembly? I have removed the key assembly on the bike. I am planning to use a relayed kill switch to disable the entire POS from the battery and the M-unit.
LOCK port on M-Unit

Also, I didn't hear on the 15A fuse. Should that be between the battery POS and starter or to the M-unit? I'm thinking the starter, but want to make sure. Also, what value fuse should I use to the M-unit, just in case? I know its internally fused, but still.
15A fuse on the starter-battery leg won't live past one rotation. You don't fuse that link. The starter draws much higher amps than 15

You can run a 15a between M-Unit and Battery POS to protect the M-Unit.

I pulled the neutral switch and it seems that the PO was having an oil leak issue and decided to glue it in. All that came out were the internals. Any suggestions on how I could remove the outer casing? I attached a photo of what came out.
Apply some heat directly to the case seams. That might release the "glue".

[AwesomeCB]

It seems the 3/4 inch thread that my tank has is the preferred method. Should my petcock have 1 or 2 fuel lines out or does it matter?

The 1976 bikes and older have one outlet from the petcock with a tube that goes to a tee that has tubes to the two carb inlets. Petcocks on earlier bikes have two outlets and two tubes to the carb inlets.

.

[piefairy]

Thanks for the info.

I did manage to join the club of 750 owners to snap their clutch lifter plate. I was tightening it slowly and working opposite bolts, but I think one of the bolt holes got hung up on the post. I was tapping the outsides of the lifter plate and I hear a "ting" and thought perhaps it was just seating itself. Went back to tightening and saw the tip move. Yarg, another part to order. I was hoping to be up and running next week. We will see.

Got frustrated and opted to stop after that, I will post up again when I get back at it.

[piefairy]

What color wire is the fuel coil? I don't see anything by that name in on my stock wiring schematic.
Typo on my part, FIELD COIL

Which lock port do you mean for the black? The LOCK on the M-unit or the key-ignition switch assembly? I have removed the key assembly on the bike. I am planning to use a relayed kill switch to disable the entire POS from the battery and the M-unit.
LOCK port on M-Unit

Also, I didn't hear on the 15A fuse. Should that be between the battery POS and starter or to the M-unit? I'm thinking the starter, but want to make sure. Also, what value fuse should I use to the M-unit, just in case? I know its internally fused, but still.
15A fuse on the starter-battery leg won't live past one rotation. You don't fuse that link. The starter draws much higher amps than 15

You can run a 15a between M-Unit and Battery POS to protect the M-Unit.

I pulled the neutral switch and it seems that the PO was having an oil leak issue and decided to glue it in. All that came out were the internals. Any suggestions on how I could remove the outer casing? I attached a photo of what came out.
Apply some heat directly to the case seams. That might release the "glue".

I got set back with the clutch, but got it installed yesterday. Back to the wiring today. I made the connections as you said cal. I connected the white wire to the white cable off the stock engine harness, all the schematics I find call it the alternator, but I know there is a field coil in an alternator. Green went to ground, and black to M-unit LOCK port. The problem I am having now is that the LOCK on the M-unit remains on, meaning the indicator light is off and functions disabled. From what I read on the M-unit wiring it is looking to a POS signal to disengage the lock, and from what I understand, the black cable is a NEG correct? If I connect it to POS, then all is fine. Just want to make sure something in my wiring isn't backwards.

I am using the M-unit blue, not sure if the wiring was different on the M-unit.