KZ650 " Wandedring" Won't track straight

Bought a KZ650 C2 last spring that had been converted into a cafe racer with rear set foot controls and a Kerker 4-into-1. The bike hadn't run in years and needed just about every kind of maintenance a neglected 40-year old bike would need. Aside from riding it out of my garage for a couple of blocks, I've never really ridden it. When I bought it, I wanted to put the bike back to stock as close as I could, so I turned it over to a friend who does motorcycle wrenching as a part-time gig. He specializes in early Z1 and KZ maintenance and is very familiar with 70s 4-cylinder Kawasakis.
He's run into a very mysterious problem with the bike's handling and I am hoping that you all can offer some suggestions.
The bike wanders down the road. After riding the bike, i could tell there was definitely some drag in the front steering. I had the wrench replace the steering head bearings with a set of proper conical bearings. While the steering is no longer "notchy" like it was, the bike is still not stable going down the road.
My friend has done some informal inspection of the fork tubes and they seem to be straight -- although he hasn't pulled them apart and checked them off the bike.. He also checked for any obvious signs of the bike having been hit hard and damaging the frame. He found nothing other than the fact that the side stand was relocated to accommodate the Kerker. The PO also hacked off the center stand mounting tabs for the same reason.
The tires on the bike have plenty of tread but were old and the rubber seemed quite brittle. So we replaced the front tire. No change. We haven't changed the back tire yet but that may be the next step.
Any ideas aside from the possibility of demonic possession?
Thanks for your help.

I'd check wheel alignment using the string technique. Check google for guidelines. Seems that something is off.

I'd change the wheel bearings just for SOP. Could be it or just part of it. Are the forks leaking? If so I'd change the seals and boots and a good cleanup inside as well as out. If the fluid level is mismatched or nonexistent, that could make it unstable too.
Poor handling up front can often be generated from the rear. Bad tire etc. even chain.
Also the forks can be twisted in the trees a touch. Doesn't take much and sighting the front tire and gap in the upper tree and how it is aligned with the center back bone of the frame will tell you that. Sometimes I've had to put my front tire up against a post and rack it a touch to get it straight again.
Sounds like you have the right idea.
PICS? NEED PICS :woohoo:
Steve

I would check the swing arm pivot bearings. I think the c2 should have roller bearings as opposed to bronze bushings? Anyway, play in the swing arm pivot could certainly make it squirrelly.

I would add to the list, bad shocks.

Did the po modify the frame at all? If he removed the rear of the sub frame under the seat and did not install a solid brace between the two sides, you may be getting some excessive frame flex at the rear.

Assuming i did not see something obvious like a broken frame weld or missing shock, my list would look like this--

Air pressure in the tires
Tire age and condition - both of them
Steering bearing condition, lubrication and torque
Forks - alignment, straightness, fluid condition and level, seals and bushings
Shocks - blown, leaky seals. If they are original, throw them away.
Swingarm bearings or bushings - wear and lubrication
Wheel and frame alignment.
Check motor mount bolts. Are they all present and properly torqued?
Since it has been cafed, check the frame for dodgy modifications

All of the above.

Plus, even tapered steering stem bearings will cause wandering if they're torqued too tight.

Good Ridin'
slmjim & Z1BEBE

By mrgem: ... He found nothing other than the fact that the side stand was relocated to accommodate the Kerker.

The muffler is on the left side? As for the frame, check to see if the steering stop peg is bent. even if it is, that doesn't necessarily mean the frame is bent.

Another check. stand in front of the motorcycle x feet away to see if the front end looks crooked. Mine was obviously akilter & I found that the upper triple was bent. I checked it on a glass table >> it rocked when pushing down on a corner. the replacement only moved a tad. There are various ways to check the fork tubes.

...

Measure the length of the fork springs. They should be the same length and within the KHI spec. If not....get new ones.

Thanks to all for your suggestions.

Couple of things: If the sing arm bearings/bushings are shot -- shouldn't I be able to detect that by putting it up on a jack and checking for play? And second, is there a tutorial somewhere (YouTube?) on how to check wheel alignment?

Thanks again to all who've offered their advice!

Youtube has many videos of the string alignment process.