My Early 1970 Honda Z50A K2

Recently picked up this Candy Ruby Red 1970 Z50A K2 from CL, frame number Z50A-279589, built 2/70, engine Z50AE-263761. Probably paid too much for it ($700) but wanted to get my hands on one. Got a copy of Jeremy Polson’s book and a Honda service guide to get familiar with these bikes. No original paperwork but it does have what appears to be an original dealer sticker on the license plate holder. While it’s an early K2 production (Jeremy has one only 440 frame s/n difference from mine) and would expect K1 parts from the previous model change, the engine number seems too far apart to be matching. The engine number would have been near the end of the K1 production. A small detail I found is that it has the brake cable tab on the engine case exclusive to the K2. Certainly not conclusive, but does make me think it could be a carryover engine from the K1 production with K2 model pieces.

Marble pattern coil has a date code 912 for December 1969 and may too be a carryover from the K1 models. Judging by the bolts, the coil has been with the bike a very long time. Gas tank (dated 700203) has some major rust issues but hoping to get it repaired this winter and keep it with the bike. The intake manifold and carb are not correct but the manifold was a nice bonus as it appears to be a vintage aftermarket Webco. Since it is an early production build, I’d have to conclude that the carburetor on the bike would have been fitted at the factory with a K1 version non-recess adjustment screw type. I do plan on keeping the bike original and replace/refurbish parts to get it back on the trail.

Someone in the past abused it enough to bend the front fork extensions, left handlebar, and fork stop tab. Exhaust system was rusted out at the c-clamp and put together with some sort of putty and aluminum tape then wired to the frame.

Put it on the bench soon after I got it home. So far, the fork has been rebuilt with new Honda parts. The bent fork tab was put back into alignment. Replaced the exhaust system with a good used one and mounted it properly. Keep going over it cleaning the frame and looking for missing parts and any other issues. The rear fender has the popular wheelie damage at the tip. The fork has taken most of my time and money for now. Once it is back on two wheels, I’ll look into getting the right carb/air cleaner. After that I hope to get it started with a temporary gas tank and see what shape the mechanicals are in.

I don't know if I'd worry too much about the # spread. I've got a K2 with a pretty big one. A swap is certainly more possible when you see a carb and intake change on something. Your carb is from something with a reserve. An older style carb from a larger bike and not a CT.
I've got some of my best parts from eBay by waiting for a long time. Sometimes takes more than a year to see something.
You can't think too much about what you paid. If they have all the parts to run that's what you're going to pay. Even if they are junk.
The model bike you have is more challenging to do with the parts a little harder to find but well worth it. Don't be fooled by the "super rare" descriptions people have. There were 10's of 1000's made.
Long live the K2

Congrats on your new acquisition. That's about going rate, these days...and not the high end, btw.

The frame doesn't appear to be bent, the rear hoops are still intact and the TL bracket still present and unmolested; those are the biggest structural issues, with hardtails. IOW a straight & solid chassis, with the bent lower fork legs being the worst of it. The mere fact that the steering stop remained on the bike was a nice bit of luck. When they break off, and that's not rare, the tank takes a beating and in areas where dent removal is damned difficult. Check the wheels for bending/warpage; this thing has been crashed...HARD.

That aftermarket intake and non-stock carb raise some concerns, though nothing deal-breaking. I don't recall if Webco made a version of that intake small enough to match the Z50 intake port. The commonly-seen CT70 flavor was ~20mm...same as the CT70 intake port. That means it's either an oversized mismatch, for this application...or...the entire top end has been swapped. Can't run a CT70 head on a 39mm Z50 cylinder but, the head and cylinder will bolt-onto a Z50 lower end, as an assembly. If you're looking for a fun rider, then the extra grunt should be a good thing. If you're after a 100-point, purist, restoration project, those items will have to be replaced with vintage originals. 49cc cylinders & Z50 heads are anything but rare.

I would be concerned about the mechanical condition of the engine. This one appears to have received its share of abuse and neglect. Running sans air filter is even worse. If the engine runs well and you're happy with it as-is, then learning how to clean the oil spinner (then doing so) along with a little solvent cleaning to remove the sludge that surely awaits discovery, should serve you well. OTOH, if the engine needs a rebuild, then I strongly recommend splitting the cases to allow a thorough inspection. I'd expect to find some tired parts, like the shift forks & pins. Regardless of what is or is not lurking inside the motor, it's surprisingly easy to cure any ailment; these little motors are remarkably bulletproof...and rebuildable.

Oddly enough, it's the OE carb & air filter that are hard to find in good condition. That said, they're not unobtainium, either.

The tank may be the most challenging project you face with this bike. There's no easy & cheap solution...other than pure luck. Fixing rust can be major work. That said, in my experience, the bottomless pit of tank repairs was a brand-new, Chinese, repop...it resembled a Z50 tank-sized potato...not a straight surface to be found! It required more bodywork than most CT70 framesets, no exaggeration. If this tank has rust perforations, as it appears, cutting, welding, etc will be needed. However, the repairs will be limited to the very bottom of the tank and any repairs done to the underside can legitimately get by with minimal bodywork. It's the topsides that matter and they look pretty good, in those photos. With a few sections removed from the underside (for replacement metal), most of the internal surfaces can be bead blasted back to clean, "white" metal. TIG welding & brazing are the best way to replace rotted tank metal and seal pinholes. Once that's been done, I'd seal the tank using a POR-15 tank sealer kit...then move onto the body & paintwork. Yes, that's as much work as it seems but well worthwhile, it'll last even longer than it already has...from the factory.