TOPIC:

Welcome aboard Nigel, hope you enjoy

Welcome to the forum Nigel: hopefully it will be a simple and quick fix for your running problems.
Cheers Tim

Thanks to everybody's posts,
I started work on the z this evening, started with changing the plugs, firing on all 6 cylinders again! The middle carbs leak fuel out the back when not running with the petrol tap on, I will take her out for a spin tomorrow eve to see if it clears itself, I have been told it's worth buying iridium spark plugs rather than standard ngk's? Also change the standard petrol tap? The tap I have is not vacuum as it has only 1 pipe out the back, the previous owner done little more than ride it to the mot and back for several years so I'm teething out the issues to get her reliable.

Regarding your fuel leaking out the back of the carb - 4 possibilities

Apiece of debris stuck between the float needle and seat

A fuel logged float. The stock floats on these machine tend to absorb fuel - the cure, Buy a set of brass floats from our outstanding member Scotch. There are quite a few members here who have bought Scotch's float and are very happy with them.

A fail needle seat, although this is rare.

And last but not least, you'll need to remove the needle seat and check the oring seal between it and the carb body. If it's not tight it will leak fuel around the seat and flood the carb. There is a reference in the FAQ section to replacement O-rings made of Viton 75 to help with the ethanol that they are now putting in gasoline. It's a really good upgrade. In your carbs are 3 different sizes and they are all mentioned in the FAQ section.

Iridium plugs are a favorite of mine, although the sparkplug manufacturers are now recommending that double platinum plugs be used in waste spark systems. The reason is that one coil fires two plugs at a time. The secondary high tension coil wire on one lead is negative and it sends the spark to the spark plug it's attached to which fires off and to ground. Then spark actually runs across the engine and returns to the second sparkplug attached to the second high tension wire on the same coil and fires across the sparkplug and then through the high tension lead and back to the coil and completes the circuit. What the sparkplugs see is one firing from the center electrode to the side terminal (normal passage of current in most ignition systems) and the second plug seeing the spark jump from the side terminal to the center electrode. As the current passes it oxidizes the electrode it left, so sparkplug manufacturers make the center electrode from materials which have extremely high melting temperatures and side electrodes of less expense lower melting temperature materials. With double platinum plugs they put a button disc of platinum on the side electrode to accommodate the excessive wear normally seen on plugs of vehicles using wasted spark systems. (and for the record, there are a lot of vehicles out there with this system). Double platinum plugs on vehicles with standard ignition or coil on plug ignition systems would be a waste of money. NGK make a series of sparkplugs called "Laser Platinum" which are double platinum plugs. I haven't done the research yet to give you the Laser Platinum replacement for the BPR6ES.

Your the second person today who's got the beast running with a fresh set of plugs. Interesting!!

Nigel,

Could you do us all a favor please and lets keep the posts about your problem with the bike running on your post " Two middle cylinders not firing" and lets just not post the same issue on this post. We've got a duplicate topic going on here and it's confusing.
Thanks,
kawboy