Topic: Look, squirrel! Or, how bike projects shift quickly; new CB750 K6 project for me

[BenelliSEI]

All sounds OK now. I usually pull the plugs at this stage. Check each lead for a healthy spark by attaching it to a grounded plug and turning over with the starter.

I often cut 1/4” of each HT a lead and screw the cap back into some “fresh” wire at this point too.

[gearsoup]

All sounds OK now. I usually pull the plugs at this stage. Check each lead for a healthy spark by attaching it to a grounded plug and turning over with the starter.

I often cut 1/4” of each HT a lead and screw the cap back into some “fresh” wire at this point too.

A)plugs are out, so will be checking resistance of wires
B) starter switch is not operational, need to chase that down...

[gearsoup]

Checked out a couple of things; plug caps and coils:

Plug caps:
#1: 1.82 M
#2: 4.9K
#3: 9.8K
#4: 33.6K

Based on that, it looks like I've got only one plug cap that is in spec. 

I then tested the resistance between 1-4 and 2-3.
1-4 measures 14.43k resistance
2-3 measure 44.6k resistance

So, it looks like I'm going to need to replace at least the 2-3 coil and all the caps. Seeing as coils are sold in pairs, I'll likely just replace both. I see that 4into1 sells what I need, are those parts considered to be of decent quality, or is it hit-or-miss

I've not done any further diagnosis on the coils, is there anything else I should check?

[BenelliSEI]

Try shortening the leads by1/4” and screwing your caps into some fresh wire. I bet it starts right up. Give it a go before spending any money.

[HondaMan]

Checked out a couple of things; plug caps and coils:

Plug caps:
#1: 1.82 M
#2: 4.9K
#3: 9.8K
#4: 33.6K

Based on that, it looks like I've got only one plug cap that is in spec. 

I then tested the resistance between 1-4 and 2-3.
1-4 measures 14.43k resistance
2-3 measure 44.6k resistance

So, it looks like I'm going to need to replace at least the 2-3 coil and all the caps. Seeing as coils are sold in pairs, I'll likely just replace both. I see that 4into1 sells what I need, are those parts considered to be of decent quality, or is it hit-or-miss

I've not done any further diagnosis on the coils, is there anything else I should check?

I can recommend the Sakura coils from PartsNmore as good product and performance, having run them on my own 750 for 2 years and installing them on several bike builds. Their part number is #17-6823, drop-in installation and a few hundred volts more spark than the OEM versions from TEC..

[gearsoup]

Are Parts-N-More and vintageCB750 one and the same? I just noticed they are both located in Stratford Ontario and have the same physical address. Curious why the split in web presence. And if they are the same, are the coils from either one the same product?

[BenelliSEI]

Are Parts-N-More and vintageCB750 one and the same? I just noticed they are both located in Stratford Ontario and have the same physical address. Curious why the split in web presence. And if they are the same, are the coils from either one the same product?

I believe they are. I used a set of their (vintagecb750) coils on my 1975 cb750F and they are performed very well.

[gearsoup]

I seem to have gotten myself into a bit of a pickle and I'm now questioning my life choices.....

The bars on the bike were tweaked rather bad, and the start button only worked intermittently (kickstarting worked just fine though). So, I figured, why not just replace both left and right switches with repro's as well as the handlebar. Oh, while I'm at it, those indicator lights (idiot lights) looked rather deteriorated, so let's replace those as well. Left side switch (and idiot lights) were sourced from vintageCB750.com and right side was sourced from 4into1.com (the vintageCB750 right switch was listed as NOT going thru the bars, the 4into1 was listed as being able to run thru the bars)

Well, color coding of both repro switches were not the same as OEM. That said, I was able to get the blinkers, horn, headlight and indicator lights working, all was good, right?
Wrong.
 Moving over to the right switch, I used my meter to check continuity of the wires (both black) to determine which of them went to the off/on/off switch and which went to the start button. Thinking I was home free, I plugged them in, clicked the off/on/off switch and immediately blew a fuse. Replaced the fuse (naively) thinking maybe it was a fluke and instantly blew the replacement.

Yes, I've got a wiring diagram. I'll unplug everything and start over, I'm certain I missed something glaringly obvious to you seasoned 750 owners.

(I also did replace the coils with PartsNmore units, ignition wires still need trimming and the plug caps installed)

[gearsoup]

I also just ordered HondaMan's fuse holder, as the terminals on mine are rather dodgy (plus local part stores don't carry the smaller glass fuses)

[PeWe]

Verify the switches functions before mounting and connecting all wiring on bike.

Either marker tape near the plug or separate notes.
Switch wire cable  color vs electrical diagram.
Some are correct, other not, might be similar.

A buzzer function on an auto multimeter will make it easier.

When doing that, it will work direct without burning fuses

[gearsoup]

Persistence, persistence, persistence.

I took a step back and examined the mess I got myself into. I said "heck with it", took the whole bucket apart and redid my work, one wire at a time, testing continuity as I went along.
Long story short; my right switch has two black wires. I was plugging the wrong one in. Once I had it sorted out, all lights work and starter engages. Of course, the repeated testing has drained the battery, so it's on the charger tonight (likely going to replace it, it's several years old).

Tomorrow night I'll move onto trimming up the spark plug leads and installing the plug caps/plugs.

[BenelliSEI]

Well done. Often it’s best to step away for a few hours and just start over!

[gearsoup]

So, I wasn't that lucky with the wiring. All satisfied with myself for getting it all put back together, I went to fire it up. No spark. Checked at the coil (2x new coils), no 12v power. So, out comes the headlight again (I really shouldn't have put it back to begin with..)

The original switch had one black wire taped off. So, I (incorrectly) assumed it was a non-used wire (despite what my diagram was showing) so I also did not connect that one black wire (there are two black wires).

Once I correctly wired everything up and flipped the switch, the 15A fuse blew!

I did some more reading, and it looks like my coils are shorting to the frame!!?? So, I unbolted my coils and just left them hanging in the air, touching no metal. After that, I replaced the fuse, flipped the key switch and pressed the start button. She ran; rough, but she was running!

Looking at the old coils, they clearly mount right to the aluminum brackets, which is how I installed mine. Am I supposed to insert some small plastic insulators to prevent any contact to the bracket; between coil and bracket and also between screw and coil)   (these were the coils from PartsNmore)

[HondaMan]

So, I wasn't that lucky with the wiring. All satisfied with myself for getting it all put back together, I went to fire it up. No spark. Checked at the coil (2x new coils), no 12v power. So, out comes the headlight again (I really shouldn't have put it back to begin with..)

The original switch had one black wire taped off. So, I (incorrectly) assumed it was a non-used wire (despite what my diagram was showing) so I also did not connect that one black wire (there are two black wires).

Once I correctly wired everything up and flipped the switch, the 15A fuse blew!

I did some more reading, and it looks like my coils are shorting to the frame!!?? So, I unbolted my coils and just left them hanging in the air, touching no metal. After that, I replaced the fuse, flipped the key switch and pressed the start button. She ran; rough, but she was running!

Looking at the old coils, they clearly mount right to the aluminum brackets, which is how I installed mine. Am I supposed to insert some small plastic insulators to prevent any contact to the bracket; between coil and bracket and also between screw and coil)   (these were the coils from PartsNmore)

The Sakura coils are insulated from the mount (like the OEM versions), so that shouldn't be an issue. Could one of the wire terminals on one of the coils be touching the frame or mounts when installed? I have 2 sets of Sakura coils in a drawer somewhere, can look at them in a little while to see it they have any 'bare spots(?) or something like that (nothing springs to mind, though). Some coils have wire terminals where their wires get soldered on (instead of them being molded over), and they often are not insulated, so watch for that.

The dual Black wires on the righthand switch are both a blessing and a sore spot: when this vendor first made the switches they only had one Black wire and it was too small (approximately 22 AWG) so it was causing voltage drop enroute to the RUN/OFF switch because it also carried the headlight's power, together more than 6.8 amps. About 7-8 years ago they added a separate Black wire for the RUN/OFF (coils) feed and the Headlight feed, which immediately improved the spark and stopped damaged insulation over time (they would slowly melt slightly and then cool, making the insulation brittle and then it could/would crack, failing the switch and blowing the 15A fuse).

It was during the 1-wire versions that I came out with the Coil Power Relay kit, which used the RUN/OFF switch to power the relay (its coil), supplying power to the coils from the main Black wire feed in the headlight, instead. I don't make them since the switches got 'fixed'.

[PeWe]

My CB750 K6 did not have any relays when I used it 1979-1990.
After restore 2012-14, I read about it on this  forum , using aftermarket ign switch with weak wiring.

Both my bikes have relays for headlight (hi-lo) and ignition. Dyna-S take more A too.
Feels good to avoid higher currents in the handlebar switches.
Thicker wirings with own fuses from battery to headlight and coils
+ Dyna-S with own fuse.

One weak point I have seen,  brake light is fed by main fuse 15A.
When an aftermarket rear brake switch shorted to ground (engine), bike stopped and lights off.
Better if it can use the circuit for rear light. I have not changed that yet.

Both bikes have stock Honda ign switches.
I saw intermittent voltage drops on my K6 with cheap switch. This thanks to voltmeter between gauges. Move key a little and better. Relay did not drop for 1V less.

[gearsoup]

The Sakura coils are insulated from the mount (like the OEM versions), so that shouldn't be an issue. Could one of the wire terminals on one of the coils be touching the frame or mounts when installed? I have 2 sets of Sakura coils in a drawer somewhere, can look at them in a little while to see it they have any 'bare spots(?) or something like that (nothing springs to mind, though). Some coils have wire terminals where their wires get soldered on (instead of them being molded over), and they often are not insulated, so watch for that.

The dual Black wires on the righthand switch are both a blessing and a sore spot: when this vendor first made the switches they only had one Black wire and it was too small (approximately 22 AWG) so it was causing voltage drop enroute to the RUN/OFF switch because it also carried the headlight's power, together more than 6.8 amps. About 7-8 years ago they added a separate Black wire for the RUN/OFF (coils) feed and the Headlight feed, which immediately improved the spark and stopped damaged insulation over time (they would slowly melt slightly and then cool, making the insulation brittle and then it could/would crack, failing the switch and blowing the 15A fuse).

It was during the 1-wire versions that I came out with the Coil Power Relay kit, which used the RUN/OFF switch to power the relay (its coil), supplying power to the coils from the main Black wire feed in the headlight, instead. I don't make them since the switches got 'fixed'.

These coils have large spade terminals that are mounted on the end, pointed vertically. The spade is insulated, but I did have to bend one to allow mounting on my oem bracket. I don't think they're touching anything, but I will check later today after I'm done work for the day.
I'm not afraid to learn new things, so what would I check with my multi-meter; continuity? What exactly am I looking for and between what points of contact? Just wires to ground and see if the circuit is complete?

[gearsoup]

With HondaMan's help, we've determined that the right side coil is defective, it's grounding out on the frame. I'll contact PartsNmore and discuss the matter with them and get another one coming.

[gearsoup]

Work has been super busy the past couple of weeks, so I've not had time to do much of anything to the CB. She's running really well, so I'm stoked about that. Currently trying to sort out my brake light. At first I thought my brake light was stuck on, so I started testing out the front pressure switch as well as the rear brake switch. Those seemed to be in working order, and even with both of them disconnected, the light was darn bright. So, I took the rear light off and did some testing. It actually looks like it's reversed, with the running light being the one that lights up when the brake is engaged. Hmm....that's odd.
Obviously, there's something wiring related, or so I suspect. FWIW, it was like that when I bought it, I figured it was just a sticking switch....

[gearsoup]

Quick investigation shows that the green/yellow was hooked into the brown and the brown was hooked into the green/yellow. Flipped them around and brake light works as it should.
Since I'd been playing with the lights for a bit, I figured I'd get the bike fired up again (I was running it this afternoon after working on the right coil) and....no spark. Cranks and cranks, nothing. Puzzled, I disconnected the green/yellow and brown just to see if maybe it was linked somehow. Nope, still nothing.

By now, my battery is starting to slow down on cranking amps, so I put a charger on it. The charger is flashing a light at me telling me I have the connection reversed. But...it's not reversed. Seems to me that somehow, somewhere, it's grounding out in the system and shorting out, does that even make any sense?
For tonight, I just disconnected the battery and it's charging now.

I'm an idiot and was overtired. Turning the start switch to ON is kinda important 
Starts right up now and brake light works 

[gearsoup]

I've got the carbs synced relatively even across all four (using the CarbTune). One thing that I'm puzzled on: air screw adjustment. From what I've read, adjusting it should change the idle. Is this "adjust all 4 and idle changes" or should I expect a single carb adjust should raise/lower the rpm?  (because it doesn't)

Also, the bike will start with zero choke, is that a symptom of improper synching (too high/low) or another carb issue, or nothing to be concerned about?

I'm running #40's and #105's, stock airbox/filter, Delkevic 4-1 pipes. OEM jets, needles and floats, 26mm float heights.

[newday777]

If this is on the K6, turn the mix screws to 7/8.

Setting by idle speed changes is done 1 carb at a time, but you need a really good ear or a digital tach that will read 50 rpm changes minimum to get it right.

[gearsoup]

If this is on the K6, turn the mix screws to 7/8.

Setting by idle speed changes is done 1 carb at a time, but you need a really good ear or a digital tach that will read 50 rpm changes minimum to get it right.

Ah, ok. So, considering I'm partially deaf in one ear, I'll rely on my digital timing light that offers an RPM output as well, I think it's in 50 increments

[gearsoup]

It's running around 1150 right now, a bit "lumpy" of an idle. If I increase the idle up to around 1300-1500 it becomes much smoother. I'm assuming I really should concern myself with the proper idle when adjusting the air screw?

[seanbarney41]

Gearsoup, when setting the idle speed, get the bike FULLY warmed before setting...that usually requires at least a 10 minute ride.  As a result, your bike may not colkd start without choke and it probably won't idle cold either.  You just have to stay in the throttle until it gets up to temp.  But these bikes are all kind of unique in this respect.  No one has an exactly identical cold start and warm up procedure.

[gearsoup]

Got the carbs and air mixture set pretty much where they need to be, probably could use a bit more fine tuning, but she runs really smooth. I buttoned it up and took it for a spin on Sunday, here are some observations:

1) Damn, the 4to1 Delkevic exhaust has such a beautiful note. A little bit noisy when you really open the throttle, but I wear earplugs (typically) and it's certainly tolerable
2) Need to put some lithium grease on the speedo cable and speedometer itself. I heard this loud whining noise once I got over 30mph, which I first thought was wind noise. Pressing on the face of the speedo made the sound go away
3) In stock trim, this bike is such a blast to ride 

When I did a general cleaning of the tank ( there is some sediment and small rust spots forming) I took the original petcock out and saw that the sock had a tear in it near the base. So, I ordered an aftermarket unit (complete) from PartsNmore and installed that in its place. Apparently, the shutoff doesn't work and I've got carb #1 that's persistently leaking (bike is on centerstand). I've replaced all the float needles and seats with new units from vintageCB750 and floats are set to 26mm.
The fuel has been shutoff since Sunday and it still drips, although not frequently. I do notice it does it as the shop warms up throughout the day, I'm guessing it's a pressure related thing?