started once, won't start again

I have an 81 kz550 standard that I've been working on for a month or so. Bought the bike in non-running condition. To make a long story short, the PO said it ran fine for years but quit starting one day. said the problem was spark. Sure enough, I found it wasn't getting spark to #1 and #4 plugs. I replaced coil with a brand new one. Also rebuilt the carbs during that time. *note: I did not replace the carb needles when I rebuilt them. everything else though*

So after I replaced the coil and put everything back together (fresh gas, oil and filter, inline fuel filter, checked entire electrical system to specs) The bike started a few times, although it was very difficult. It ran enough for me to take it around the block once. Seemed to run ok.
The very next day, without doing anything, the bike would not start. Pulled the pickup cover off and touched the pickups with a screwdriver to force a spark. It def sparked because it turned over once when i did that. After that it started again but did not run well and would not idle.

Next I replaced the ignitor. No difference. I have yet to buy a new pickup set, as I am trying to rule everything else out before I spend the $150 for dyna s pickups.

Anyone have any suggestions as to what the problem is? I'm nearing the end of my limited knowledge in this area lol

so to recap

New coil, new ignitor, carb rebuild, general tune up and maintenance, still no start

Ok first of all, I have to ask if you adjusted the float levels and synced the carbs when you rebuilt them? Does the bike have compression on all cylinders? Next, make double sure that you actually get spark on all of the plugs. I would pull the plug and crank the motor with the plugwire still attached. If you get a nice blue spark, and you passed all of the above tests, then it comes down to timing and valve clearance. I would procede by pulling the valve cover, and checking the vavle clearances. Also check to see that the cam timing chain hasn't jumped while you are in there. All that will cost you is a gasket.

You should check to make certain that you are getting full battery voltage at the coils red wire, within 1 volt of battery, and it should be nearly 12v. Then when cranking the starter check to make sure it does not drop below what is measured at battery during cranking. If you have a bad Ignition switch or a loose or dirty connection this may be your starting and running problem. Do you have a manual? You can put 12v from the battery to the positive side of the coils with a test lead and measure voltages again to see if there is a resistance in Ignition feed circuit. Don't forget that some times it can be a poor fitting or defective fuse causing low voltage/ current on your circuit.

thanks guys
I'll get started checking these things tomorrow. Last time I checked spark (after replacing coil 1/4, before replacing ignitor) I had spark at all four cylinders, but they didn't seem to be the same. some seemed weaker and possibly a little orange instead of bright white/blue. I'll start working on checking the voltage at the coils first. I'd like to eliminate or diagnose any electrical problems first. If that's a bust then I'll move on to checking valve clearance and timing issues.

Oh yea, another important thing to note..when it was running, there was a fairly loud clanking/knocking/rattling sound. Not quite sure where it was coming from, but I know it was not exhaust related and it seemed to mostly go away as rpm's increased. Could this be and indicator of improper valve clearance or anything else serious? it didn't sound good to me...

thanks again

Could be serious, or maybe a cam chain. Have you ever replaced the cam chain? Does it have the stock auto adjuster, hard to say but this is pretty common.
And these are known for a primary chain rattle as well that can be amplified by miss adjusted carb sync and low Idle speed.

I believe it has the stock auto adjuster, and no I have not replaced the cam chain. I've never opened up the engine at all and the bike does have 50k miles on it, so I wouldn't be surprised if it needed some things adjusted...

I pulled the sprocket cover off today and found the front sprocket to be a little loose, the rear sprocket pretty worn out, and the chain was loose. Guess im going to replace all three..

That's the correct way to replace the drive system as new parts are quickly worn out by old parts.

The chain usually developes tight and loose places causing the sprockets to wear out/creating hooked teeth.

lol the rear sprocket looks like a circular saw blade...PO must have not changed it for quite some time