Z1OwnersClub GB

Can someone explain the pyshics behind why cylinders run better with the plug cap pulled partially off.
On my 650 with the caps pushed fully on i can hear it miss every now and then, with them partially pulled off so you hear arcing between cap and plug it runs as sweet as a nut.
Is the resistance not higher with them partially off?
Coils and electrickery all good. Plugs and caps all new. Timing and points all spot on.
I don't understand why this should be so not sure what to do to remedy.

New plug caps required!

did you use cheap ngk plugs as there are load of fake copies on e bay & they are shite.

They are ngk, but not fake ones. An explanation on z650 forum says "Total gap size the spark has to jump increases, so HV voltage across the gap also does. Thus, this has the effect of increasing the spark enegy. Increasing the spark plug electrodes gap has -partially- the same effect, as the spark energy across a larger electrode gap would be higher than that across a smaller gap" does this sound right? Not doubting it but electricky is exactly that to me.

Had the same problem on my Z250, which I posted on here, found that when I changed the plugs to Iridium, it was much better, also found that if the battery is not fully charged up it makes it worse at tick over.

A later post on z650 forum says that all the documentation I have from 1976 had a latter correction made saying plugs should be b7es not b8es. B7es is one grade hotter. Swopped to a new set of those and the issue seems to have disappeared.
Who have thought 1 grade of plugs would make so much difference. I'm not sure its not just coincidence but I'm not complaining.

as already said faulty plugs

This is a trick shown to me by some guys in the CX500 club. I had a CX500 would not start. Two guys from the club came over and plulled the caps off and just about rested the caps on the plugs. Hey presto started first push of the button I asked them why it did this, they told me it made the resistance higher causing a greater spark. And normally this is a fault developing in the ignition system. But who gives a shit, if this trick gets you back home

warren3200gt wrote:A later post on z650 forum says that all the documentation I have from 1976 had a latter correction made saying plugs should be b7es not b8es. B7es is one grade hotter. Swopped to a new set of those and the issue seems to have disappeared.
Who have thought 1 grade of plugs would make so much difference. I'm not sure its not just coincidence but I'm not complaining.

The number is only heat grade - insulator amount - which was not the reason it started to work.... t'was a duff plug.

DENSO iridium's have sorted out a couple of badly running bikes (which had NGK) in my opinion

NGK plug caps, copies or not, have built in resistors which are utterly shit and often go tits up. Result, poor running, misfires etc.

Ditch the NGK caps alogether and buy some without resistors in!

Pigford wrote:

warren3200gt wrote:A later post on z650 forum says that all the documentation I have from 1976 had a latter correction made saying plugs should be b7es not b8es. B7es is one grade hotter. Swopped to a new set of those and the issue seems to have disappeared.
Who have thought 1 grade of plugs would make so much difference. I'm not sure its not just coincidence but I'm not complaining.

The number is only heat grade - insulator amount - which was not the reason it started to work.... t'was a duff plug.

DENSO iridium's have sorted out a couple of badly running bikes (which had NGK) in my opinion

Hi Pigford, what's the plug number for the denso iridium Pleas.

Z 1 900 '73-'77 W24ES-U IW24