Hello from Northern California

Hello all y'all,

I just got my first bike, a 1979 KZ650 this year and it's been full of good learning so far. Took that motorcycle safety course since I've only ever ridden two stroke bikes off road, found out which local bike mechanic is good and which one is really not good, and have finally landed on working on this bike myself with some help from Clymer and KZRider. Here's the bike!
 
 

And I guess my first question is hopefully about timing and advance, but we'll see. First, I'm currently having two issues: intermittent low power that shows up in various ways and gets worse after thirty minutes of gentle riding on flat land, and gas getting dumped into the exhaust cooking the paint off my exhaust pipes.

So far I have:
1. Had a not so great mechanic rebuild (sonic clean and full carb kit from unknown) an sync the carbs. (Around March)
2. Had a great mechanic rebuild (full carb kit from kawasaki) the carbs, replace the intake boots and clamps, clean/reseal the carb to manifold boots, flush the fuel lines, lightly drain and clean out the tank, sync carbs. (In September). Checked compression and spark (basic compression test and strong visual spark). Replace the air filter and seal a crack in the air fitler cap screw thing.

I didn't ride it until after the first mechanic had done work but when my friend test rode it for me he noted that it lacked power in similar to how it's behaving now, so I believe the issue predates any work I've had done. So, since I believe that the basics of fuel, air, and spark *seem* to be there I started looking into timing today per the advice of the Clymer manual. I warmed up the bike for 10ish minutes, rode around the block and didn't notice any lack of power. I checked the timing with this xenon light I got from harbor freight and while idling at ~1200rpm I see the timing lined up at the F mark for cylinders 1 and 4. Then when I slowly accelerate to 3000rpm things get weird, the timing seems to jump around a bit but does *seem* to move towards the T mark for 1.4. Then when I get around 3000rpm I get some jumping back and forth between 1-4 and 2-3 cylinders and it's hard to tell because also around this rpm the light will start not blinking, taking big 1/4 second breaks between blinks from 3500rpm and up, sometimes just staying off. I'd also like to note that the original points were replaced by what looks to be a Dyna S electronic ignition system, which I've had trouble both identifying and finding manuals for.

Maybe I have a bad timing light?
Maybe the wiring for the dyna s has some resistence?
Maybe I'm checking timing when I should be checking something else?
Maybe the timing advance mechanism needs to be cleaned and lubed because it's sticking?

I also had a few more basic questions.

1. Since I've had this bike for a year I've already had rust and gunk in the jets twice even though I ride pretty regularly (two tank refills a month minimum). Is it worth it to put inline fuel filters between the tank and the petcock (can this even be done on this bike? I've heard things about a vacuum petcock and haven't looked into it)?
2. One of the mechanics recommended I pick up this $50 3 step tank clean and seal kit and clean the crap out of and reseal the tank, is that worth doing?
3. Since a bunch of the paint has been stripped off the exhaust is it worth it to pull the exhaust off, sandblast it, and repaint it? Or should I look into some of these other aftermarket exhaust systems?

Anyway, happy to be riding a KZ and looking forward to learning how to keep it in top shape.

Welcome from Canada.
Nice 650!

A fuel filter is a good idea.
Just add one to the the fuel line somewhere.
The vacuum line should be smaller diameter, and it usually connects to carb #2.
No need to touch the vacuum line.

As far as lining the tank, it all depends in what condition it is in. Inside.
I've been lucky that my tanks have not been rusty.
A little may be okay, but a lot I can see isues with.

The exhaust is your call:
What codition is it in overall?
What brand?

I just bought a 4 into 1 Delkevic Stainless Steel on sale for $399 US$ off eBay for my 1000.
Have a Delkevic on the 650 for close to 10 years now.

The timing light I cannot help with, as the one I bought years ago, used, never really worked.

Someone will chime in with an answer.

You could check what voltage is making it to the coils.
Ideally you want close to 12 volts, but some stock wiring will loose some power, giving maybe 8-10 volts at the coils.
In that case, a "coil Mod" may help there.
Where a relay is utilized to power the coils more dirrectly, giving more power.

 





 

Welcome from the UK

Welcome. The 650's are really good bikes. 
 Carb "rebuilds" cover a lot of ground. Were the stock jets replaced with unknowns? I would start with pulling the carbs and finding out what was put in there and go back to stock, factory jets and settings. I avoid generic "rebuild kits". It looks like you have the stock airbox so you can stay within a size or two of the pilots and maybe go up on the mains to compensate for the exhaust. As for that, I would do a wire wheel treatment and BBQ paint touch up until you get it running correctly. For the timing, make sure your advance is not stuck and rotates freely.
One thing you should do is check your valve clearances. It's not hard but does require time and patience and is one of the most overlooked maintenance items. 
Good luck. 
 

Welcome to the fun! Nice looking machine you have there.