Kawasaki GPz305

I recently acquired a 1996 GPZ305 with just 6500 miles on the clock. It
started first touch and ran beautifully for 600 or so miles, and then
just died from about 7-8000 rpm, no warning, no pops bangs or unusual
engine noises.
I've got a nice fat blue spark to each plug, I've got fuel in the
carburettor bowls and the plugs are wet after a few seconds on the
starter. But nothing!!
Compression is so tight, I can't move the bike without dragging the
rear wheel.
One thing I did try though, I turned it over first with the plugs
connected, and then without. There was no difference in engine speed. I
would have expected that big fat spark and fuel to have given some
assistance. Am I losing that spark under compression, and if so, why?
It also occurs to me that the fault must be common to both cylinders,
since I would expect the engine to try to run on one cylinder

Has anybody got any ideas?
Gordon.

 

If you want to bump start a motorbike, the way GP riders used to have
to do, the trick is to push the bike backwards a bit with the clutch
lever pulled in to break the clutch plates free. Then put the
transmission into second gear, and do your run and bump...

That is so hot and sweaty and physical. I much prefer my electric
starter button...

Does the engine turn over rapidly on the electric starter with the
spark plugs removed? If it still turns slowly, there's a mechanical
problem with cams or bearings, or something binding, like the
Frankenstein-designed starter clutch used by Japanese motorbikes...

Fuel-wet spark plugs indicate something like a stuck carburetor float,
oil-wet spark plugs mean something bad has happened down below, in the
engine's mechanical bits...

And, many riders don't have any idea of how to start an engine that has
no real choke plate, as such...

Carburetted Japanese motorbikes usually have a starting enrichener,
which is just a tiny carburetor in a passage bypassing the main carb
throat. If you open the throttle while the "choke" lever is in the full
ON position, you just rob the enrichener of the vacuum it needs to suck
gasoline through the separate starter jet. The engine may try to suck
gasoline past the needle jet/jet needle orifice instead, and that's
just too much fuel for the engine to burn, the spark plug gets wet, but
the wetness is clear gasoline, not dirty-looking oil...

 

It's a GPz305, one of the most short-fused engines Kawasaki ever made.
It's probably blown up and terminally so.

 

That's disappointing news. I thought of it as a good urban or
starter bike. It had a belt drive, did it not?

 

Indeed. And very good it was too.

However, the engine was an overstretched version of the 250, which was
already pretty much on the limit, reliability-wise.

The 305 was a disaster - top ends went AWOL, camchain tensioners failed,
and crankshafts rumbled into obivion. Seriously, this was one very, very
nasty engine. Shame, because the bike itself was a hoot to ride - fast,
economical and fun. I rode one from London to the Bol d'Or in the south
of France, and rode it back two-up (800 miles each way!).

There are some which have been cossetted from new, never thrashed, and
the oil changed every 1500-2000 miles (which helps), but by and large,
they're unmitigated disasters.

I once met a Kawasaki dealer who could recite the part numbers of the
crankshaft and other essential engine bits from memory. Not a good sign.

 

Interesting point. This bike usually started first turn with full
choke, but while checking for wet plugs I probably opened the throttle.
Even so, surely something would have happened?
There are no indications by way of oily plugs or noises to suggest any
mechanical damage inside the engine.
Thanks so far