Noise

****...
Just had one of the best days you can have without taking your clothes
off...
Got the Z650 out and went for a spin with the fair Jane on her 750 Virago.
We live not too far from Newport, S Wales and went north via Builth Wells to
the Elan Valley, very nice. Went to Aberystwyth and headed back, all again,
very nice. Superb roads and scenery.
However...
The old Z is misbehaving... Under load (i.e. lowish revs and biggish
throttle opening) it kinda jumps, sounds for all the world like a chain is
jumping off a sprocket (not so, all new and started doing it with the old
set) It's almost like it jumps out of gear and back in, it never jumps out
and stays out, and as I said only does it under those conditions. If I give
the motor its head and gun it from scratch it behaves fine and goes like
shit off a shovel. Does it in all gears, Any ideas??? Worn gear selector
forks maybe??
TIA
Ian

 

Sounds like you're lugging it, too low revs for too high a gear. If you're
used to it being smooth in this condition, check timing, mixture, carb
balance, air filter etc. I seriously doubt there's anything wrong with your
gearbox.

 

Gear selector forks select gears (duh), so they affect gear changing.

If it does it in more than one gear, it's not a particular gear,
either.

My best guess would be that the primary drive chain could be jumping,
but I've never heard of that happening before. Usually, they just
rattle a bit.

As Platy says, don't make it lug high gears at low revs with wide
throttle openings. To quote the old doctor gag :

Patient : Dr, it hurts when I do this
Dr : Well, don't do that, then.

 

Yeah, OK, it was late when I posted...

Yeah, I'd worked that out...

I'd been thinking on those lines but it would have to have a hell of a
stretch to jump teeth, wouldn't it? I'd have thought enough to mash the
motor into a pulp! It rattles like buggery at tickover unless I twiddle the
knob to get it to idle at 1250 plus and I assume that it's the primary chain
that's doing the rattling, but it's done that since I had the bike. This
jumpy thing is really weird though, never used to happen and it's definitely
getting worse. (Like these things ever get better...)

I don't over 'lug' the engine, I mean this is like pulling away from a
roundabout in 2nd or 3rd at about 3-4k rpm with half or a bit more throttle.
I feel a strip down coming on, JUST what you don't want with this superb
weather :-(
Anybody got a pristine Z650 motor for a packet of peanuts????
Ian

 

Ian says...

Just a thought, but have you had the carbs balanced yet since you
stripped them right down? Unbalanced carbs will make an engine sound
like a bag of nails on tick over and make it feel a bit lacking in the
performance department when the throttle is blipped.

 

"> >

No I haven't, but since when did unbalanced carbs make a bike feel like it's
jumping in and out of gear?
Have been out again on it this evening and it goes just fine, performance,
gear changes etc are no problem... Just if I let the revs drop below about
4K and open the throttle wide it sounds for all the world like a chain is
jumping a sprocket or gears are missing each other. You can feel it too!
**** it... I'll ride it into the ground till it won't go any more and then
I'll maybe have an answer
Ian

 

Ian says...

Fair point, but it could account for the slappy chain noise you have at
tickover. Unbalanced carbs will cause snatching of the camchain.

Have you checked the condition of the front final drive chain sprocket,
the one that always gets neglected cos it's a pain in the arse to get to
and replace?

 

Primary chains do rattle on those motors, you're right. And I agree,
that if it was loose enough to jump then it's worryingly loose!

BTW, 1250 is about the right tickover speed, so if the carbs are
balanced (see Lozzo's post) and it still rattles like a bastard then
the primary chain probably is knackered

You pull away in 2nd or 3rd? You don't mean that, do you?

 

"from a roundabout" "at about 3-4k"

 

Brand new chain and sprox, only done about 300 miles...

 

God no! I mean I haven't stopped at the roundabout, just gone round it
slowish and accelerating the other side!

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Ian

Front sprocket nut still nice and tight, is it?

 

Certainly is, it was doing it before the change anyway, was part of the
reason for changing chain and sprox. Had it in my mind that the front
sprocket was knackered and the chain was slipping round it. chain was fucked
anyway, had tight and loose spots and the sprox were well on their way.

 

Evidently.