TOPIC:

At the very least, take it back to the mechanic and say "Hey man what gives? $2000 and it only runs for a day?" If he's good enough to charge you $2000 to do "Work" then that should have also included a total assessment of the bike prior to any work being done. I would be ashamed of myself if I charged a guy that kind of money and it only ran for a day. Shit, if you doubled that money, you could have bought a late model bike and had a good solid runner for years before a teardown.

Re: Valve-stem seal replacement
 Not many options available unless you remove the head.  I made this to do my seals.  A fair amount of work to make, but a lot less work and expense then dealing with a cyl-head removal and it works like a dream !   

www.kz1300.com/index.php/forum/engines/2...compressor-1-4#17527

As others have pointed out, it's not possible for half the coil circuit to fail since two cylinders are required to 'make' the spark circuit complete.  Having said that, the spark plugs on the 'dead' cylinders may be so fouled they're completing the circuit without sparking.  If it was me, I'd take a good look at the plugs on the dead cylinders and if they're gross looking, replace them to see if that makes a difference (you could try a good cleaning first but if that doesn't make a difference, I'd try replacing them with new next.  If that fixes your problem (even temporarily), then you have to look at what's causing the fouling - which may be nothing more than just running it on 3 cylinders while troubleshooting.

for sure....next lifetime i will come back as a bike mechanic i think....here in oz its about 130 an hour and not uncommon to charge 600 to 700 for a simple tune up...    fork seals is about 700....its a scam.

i ll keep everyone posted on further developments

just a follow up from and the developments on this here, z1300.

first of all, thanks to everyone who contributed.
no words were wasted as i have taken everything said, on board.

.....much appreciated.

so, i had my suspicions on the ngk plugs that the previous mechanic had put on the z1300, because i had previous experiences with ngk plugs on my guzzi 1973 v7 sport.....i changed over to bosch platinum on it, and 500 kms later the guzzi still runs like a dream.

so, i ordered 6 denso W20EP-U through ebay and today replaced the new ngk plugs for these denso's.

FIRST TOUCH of the right hand button and she roared on all 6.
i haven't had the time to ride it yet.....but i will.
my next step will be to put back those ngk plugs and confirm this to be the problem.

to say i 'm happy is an understatement.....

I've never had a bad set of NGK's but I have had a set oil soaked or carbon tracked down the center electrode causing a short to ground(no spark)  
I'm a firm believer in KIS principal. Keep It Simple. We tend to believe that "all of these electrical problems will happen to me" rather than throwing in a fresh set of plugs because the most likely failure in a reasonably good ignition circuit is the spark plugs. They are the omly item in the service manual known to need replacing.
Now that you know that the plugs had an early failure, the next time this happens you'll change the plugs first. The real issue is what's causing the failure. This is where the " Old Champion spark plug cleaner tester" was worth its weight in gold. You could install the sparkplug in a test chamber and then apply spark and add "cylinder pressure " and watch at what point the plugs would fail . New plugs would fail at around 150 psi test pressure. Good used plugs would fail around 80-90 psi test pressure. Bad plugs would fail below 50 psi test pressure and you could see the failure down in the cavitiy of the plug or a cracked center insulator would track down the outside of the plug. Really neat to watch.
Back in the late 1970's, it was a common practice to offer a sparkplug cleaning service rather than a new set of plugs. Now plugs are cheap so the old champion plug cleaners have gone by the wayside except for the aircraft industry. Those plugs are over 450 a piece and oil fowl like a 1942 Harley.

Youtube video of a similar tester