Topic: 1973 K3 Bittsa arrived today, a bit baffling

[newday777]

3/73 date on the frame so it's not an early K3, it has K2 forks and unicorn top tree, gauges, a K1 wire harness and ignition switch (round connector) and it has K4 motor case numbers, the motor kicks over thankfully.
My guess, maybe a wreck rebuild at some time? Maybe the motor took a hit and busted the cases??
I don't have any history of this bike at this time other than it was stored the last 25 years in a storage container.
My friend that I got it from, is going to try to get hold of the previous owner to get some more idea of it's history. It was last registered in 1988.

[HondaMan]

Yep, 3/73 was about when the unicorn triple tree faded out to the new one.
Does it have the 657b carbs? Then it should also have the plastic floats inside. Some came with an overly-generous #110 mainjet, and were real plug-foulers for it.
It looks like there is just one fuse in the fusebox? That's early K3, as the [accursed] 'safety module' made its appearance around 4-5/73.If yours has wiring for a 'safety module', look for the bracketry of a sidestand switch: I only saw them on the earliest K3, but things were pretty hectic at Honda in those days, trying to get them out the door with whatever they could put together.

If you're going inside the engine: the early K3 heads had the least handwork of all the early bikes. and the ports were quite rough. You can improve the breathing significantly in those heads with just a Dremel.

[newday777]

Thanks for replying Mark, I wondered if the unicorn was original still at that point and the K1 harness/single fuse panel(the K2 I got last week has both also)
Yes it has 657B carbs on it, I haven't opened the bowls to see if they have plastic floats but the K2 carbs, 657B also have the plastic floats when I opened them to do a cleaning on Friday.

A sidestand switch? I didn't know that Honda was playing with them that early. My 83 GL1100 didn't have a sidestand switch, it was probably on the GL1200 though?

Good to know about cleaning the ports up with a diesel, I have one with the cable extention. But it has K4 motor case numbers?? -2334851

[willbird]

Yep, 3/73 was about when the unicorn triple tree faded out to the new one.
Does it have the 657b carbs? Then it should also have the plastic floats inside. Some came with an overly-generous #110 mainjet, and were real plug-foulers for it.
It looks like there is just one fuse in the fusebox? That's early K3, as the [accursed] 'safety module' made its appearance around 4-5/73.If yours has wiring for a 'safety module', look for the bracketry of a sidestand switch: I only saw them on the earliest K3, but things were pretty hectic at Honda in those days, trying to get them out the door with whatever they could put together.

If you're going inside the engine: the early K3 heads had the least handwork of all the early bikes. and the ports were quite rough. You can improve the breathing significantly in those heads with just a Dremel.

The K3 I have did not have unicorn, wish it did, did not have side stand switch.

[newday777]

Well no sign of wiring for a sidestand switch on this bike.
I opened the carbs and for how dirty the outside is,  the inside was the cleanest of the 8 sets that I have opened and cleaned in the last year. No broken float towers either thankfully. The slow jets are clogged a bit so these carbs will get the full treatment ultrasonic cleaning.
And yes Mark they have the plastic floats, but they have 105 Keihin mains, not the110s you expected. And the single fuse panel

[HondaMan]

Interesting combination of parts you have there!
The [silly] sidestand switch only showed up in the shop I had on a couple of bikes, and they were not local riders IIRC, but touring thru. They were both very early K3 bikes, brand-new at the time, less than 1000 miles showing. They had the big "safety module" under the left side cover that was, inside, a small lamp pointed at a photocell, and having the sidestand down (that switch) or the tranny not in Neutral (light ON) would turn ON the lamp, and the photocell pulled in a relay that enabled the START button. The sidestand switches got removed (ON when deployed, like the NEUT lamp circuit) quickly (broken, mostly I heard then) and the wye connector for them, which joined to the NEUT light's connector under the left side engine cover, got clipped off. This stopped the circuit from working, turned it into a sort of K2 with a requirement for the NEUT to be ON for STARTER button to get 12 volts. The other side of the starter solenoid was grounded. This got shortened to the diode that everyone knows today, and the 'extra' switch got moved up to the clutch lever instead of the sidestand.

Dumb...the lamp in the "safety module" was incandescent, so road bumps would eventually break the filament, failing the thing. It wasn't repairable, either.

[BenelliSEI]

Nice find! What make is that rear wheel?

[CycleRanger]

Nice find! What make is that rear wheel?

Looks like an Invader perhaps.

[willbird]

Interesting combination of parts you have there!
The [silly] sidestand switch only showed up in the shop I had on a couple of bikes, and they were not local riders IIRC, but touring thru. They were both very early K3 bikes, brand-new at the time, less than 1000 miles showing. They had the big "safety module" under the left side cover that was, inside, a small lamp pointed at a photocell, and having the sidestand down (that switch) or the tranny not in Neutral (light ON) would turn ON the lamp, and the photocell pulled in a relay that enabled the START button. The sidestand switches got removed (ON when deployed, like the NEUT lamp circuit) quickly (broken, mostly I heard then) and the wye connector for them, which joined to the NEUT light's connector under the left side engine cover, got clipped off. This stopped the circuit from working, turned it into a sort of K2 with a requirement for the NEUT to be ON for STARTER button to get 12 volts. The other side of the starter solenoid was grounded. This got shortened to the diode that everyone knows today, and the 'extra' switch got moved up to the clutch lever instead of the sidestand.

Dumb...the lamp in the "safety module" was incandescent, so road bumps would eventually break the filament, failing the thing. It wasn't repairable, either.

The K3 I have was made 10/72 and serial is CB750-2204xxx. No unicorn and no side stand safety switch.

[newday777]

Nice find! What make is that rear wheel?

Looks like an Invader perhaps.

Yes it is an Invader wheel

[Stev-o]

The thing with these old bikes with no documented history is you never know what has been changed out or for what reason. Been there...

[MauiK3]

My 10/72, bought from the original owner, does not have a side stand switch, no unicorn, has a safety module which I bypassed, no clutch switch, engine numbers are correct for the period.
Head and cylinders were improved by Hondaman!!
Runs great
weird mix in those days

[Mark1976]

   Bittsa , baffeling, same thing... the deeper ya go the more ya think, "WTF".
The rack looks pretty good though, especially since it still appears to have keihin brass.

[HondaMan]

My 10/72, bought from the original owner, does not have a side stand switch, no unicorn, has a safety module which I bypassed, no clutch switch, engine numbers are correct for the period.
Head and cylinders were improved by Hondaman!!
Runs great

Sometimes I think the Honda planners had set their route to the new injection molds and other bike 'cheapening' things they were going to do with the K4 when the K3 began. Then they moved everything to the New Factory while most of the K3 were made at the Old Factory before it quit making the 750 at all. This seems to be why so many K3 bikes had poor heads (unfinished in/exhaust passages and combustion chambers were common) and everything from K1 cam bearings to the K4 types - and half a dozen other things in the engines. There might be a K1 clutch housing, and K0/1/2 shifter drum (or the new, improved one) or a K4 style clutch outer with a single wide-tab clutch plate on top of the stack, but without a slipper sprung plate, things like that. The wiring was originally more complex with the safety module thingie, and got simpler with some unusual jumpers tying things together in the headlight bucket (wire colors didn't match up, things like that). I think the K3 will teach the user more about the 750 than any of the others!