Motorcycle Safety & Driveability: Honda handling problems, wheel bearing, two planes

Question
I have a 1976 Honda 750f (Supersport) that has a most peculiar handling irregularity.  During cornering and on some less perfect roads there is a feeling of 'drifting' or 'floating' whereby the bike seems to be moving in two separate planes, almost as if the front wheel and rear wheel do not track correctly.  I have checked the rear chain adjusters and got the sprockets lined up and rear wheel in line with the marks on the frame. I also rebuilt the front shocks.  There seems to be no slop on the steering head or wheel bearing either...  HELP!

Answer
I'll have a go at this, although the information you have given poses as many questions as it asks!

Remember first that this bike is over 30 years old and any number of it's components could be well passed their. best performance. What do you know of the bike's history? Has it been down the road at all? Is the frame straight?

You've discounted wheel mis-alignment and steering head bearing shake, so I'll not go there.

Let's start with the obvious, but often overlooked possibility: Tyres. Are they a modern, matching pair? Are they at the manufacturer's recommended pressure, e.g. 42psi rear and 36 psi front on many bikes now. Are they in good condition, not cupped or out of shape?

Next, you don't mention the rear suspension. Don't know how many miles it's done, but it quite possibly well passed its best. If you've re-done the front forks and got them quite stiff, this will emphasise the sloppiness of a poor rear unit.

Your description of feeling like the bike is on two planes is typical of knackered or poorly adjusted suspension, where the unit cannot deal rapidly enough with the number of undulations in the road surface in a given number of seconds. Put simply, the bumps are happening faster than the suspension can respond. Instead of absorbing the bumps, the bike starts to skip across them.

If memory serves me correctly from riding these bikes first time around in the early 80s, the forks also had a tnedency to "walk" in long sweeping corners and some riders had them braced to prevent that.

Hope this helps, but feel free to come back with a follow up if you wish.

Regards

Alec
http://www.alecgore.com