I'm pretty chuffed to have my XZ550 riding like a proper motorcycle at last. Lovely rich sound, great acceleration out of curves and no more stumbling when I need power the most. The bike still looks like a shitty rat bike, but at least I now have some incentive to start tidying it up after a couple of years fiddling to get it to this "happy rider" state.
This thread is to give some idea of how I solved stuff on my machine and to encourage others not to give up. In my case it boiled down to electrics, fuel supply and carburetion. Hopefully others will add their wisdom and experience to this post.
Electrics
1. Check coils according to the manual, clean up frame ground contacts, replace spark plug leads, plug caps and spark plugs. (I put in Iridium plugs)
2. Replace starter lead with a heavier guage to reduce voltage loss. (The TCI unit works erratically when cranking voltage drops below about 10 volts - never try to start from cold with your lights on!.)
3. And of course a decent battery and a stator/regulator that is charging it. To keep an eye on what was happening with the electrics, I slapped on a waterproof $10 Chinese voltmeter. - a great confidence booster
4. Others will recommend new fuse blocks, wiring harnesses and so on. - Not on my list of priorities at present.
Fuel
1. Fuel must be clean and rust free. At a minimum an inline filter is a must. Having a POR'ed tank is desirable. I haven't done my tank yet, but I put rare earth magnets in my carbs and filter to help suck up rust sludge. Works well.
Carburetion
1. In my experience, the biggest culprit causing bogging is air leaks into your system. Replace all vacuum hoses, especially those to your petcock and petrol pump. Make sure your YICS is airtight or throw it away and cap the ports
2. If you can find new ones, replace your carb boots or coat the old ones with several coats of liquid rubber to seal the cracks.
3. Totally strip your carbs, remove all jets. Thoroughly clean every part with a varnish solvent. Then blow out all air passages with compressed air. Repeat! Access to an ultrasonic cleaner with solvent is a bonus.
4. Replace all O rings and the throttle valve seals
5. Replace all jets with new ones. I re-used my emulsion tubes OK. Reassemble carbs. Make sure the floats are set to spec and that the accelerator pump is working exactly as described in the manual.
6. Check that the vacuum flapper in your airbox is working OK (do this initially by sucking on the vacuum tube)
7. (Adjust the valve clearances to the spec in the manual. - I haven't got the special tool required so I haven't done this important stage yet. looking forward to more improvements when it is done though)
7. Install the carbs into the bike. Setup up a pony gas tank. (I use an old motor-mower gas tank strapped to the headlight) Block off any vacuum ports that aren't needed.
8. Start bike and adjust carbs and idle screw until warmed up and running reasonably
9. Sync the carbs so that each carb draws the same vacuum at idle. Tweak the mixture screws for best idle, then recheck the sync for balance.
10. Install the airbox with its vacuum and breather connections. Adjust the idle screw to bring idle back to up 1300 revs. Check your vacuum flap is working when the bike is revved hard. Shining a torch through the air intake helps to see if it is working ok.
11. Tighten down all joints, re-install tank,Take it for a spin. Whoop for joy or cry in frustration and start troubleshooting.
Jetting your carb. I am no expert here, but here is what worked for me.
Before refurbishing the carbs, I found that the stumble was reduced when I had the enrichening circuit (choke) just active. I figured my idle was lean and probably my mid-range jetting was lean as well. Therefore I reduced my top Idle air jets down to 120's so that less air and more fuel was drawn in on each stroke. (The idle jets are standard #60's) Next I increased my main jets size to 125 on the front cylinder and 130 on the rear to give the mid and upper range more fuel. I haven't tweaked the accelerator pump settings yet, but the actuator rod length is about 60 mm
Jetting will be different for others depending on their exhaust setups. Mine has standard headers and mixing box and stainless steel mufflers. It is probable that my exhaust is fairly close to a standard setup.
Next, I will drop the plugs out and inspect the colour to make sure I am not running too rich and wasting gas.