no start after new rings - zephyr 550

I bought a ZR550 parts bike a while ago, but it was in such good shape that I decided to try saving it. Despite having only 8,700 miles, it didn’t run—so I went for a full overhaul to start fresh.I honed the cylinders, installed new rings, and meticulously refurbished the carburetors using OEM float needles and set the fuel level per the FSM. I also did the usual maintenance: oil change, new battery, etc.Yesterday, I finally got everything back together… and it won’t start.It cranks fine and will occasionally fire up very briefly, but I can’t get it to keep running.

• Valve clearances are all in spec.
• Cam timing is set per the FSM at 1&4 TDC with #1 cam lobes pointing outwards.
• It’s getting spark at all four cylinders.
• Coil wiring is correct (green coil to 2&3, black to 1&4).
• Compression is solid: 124–127 psi across all cylinders.
• Scoped the cylinders—they look good. A bit shiny, probably from all the gas during repeated start attempts.

So it has compression, spark, and fuel. By all logic, it should just f**king start… but no joy.What am I missing?Open to any and all ideas. This is my third head rebuild, and the first time I’ve run into this issue.

Cam timing 180 degrees out?  It's easy to do (don't ask how I know).  

I mean, anything is possible.  I did install them in this orientation at TDC for 1&4, with the #1 lobes pointing out (the pic is from Loudvx's kz550 Amazon page). 

 

One thing I can be confident in is that the engine has compression. I'm seeing spark but maybe the spark timing is out, either because I have the cams installed 180 degrees out, or because there is a fault in the ignition system.  I do have an spare ignition system I might try swapping that in. I'm 99% confident the carbs are clean (never say 100%) and it's getting fuel, but it's always possible they aren't.  I'm wondering if I can try spraying some starter fluid into the airbox to check that aspect.  Or do I remove the airbox and spray directly into the carb throats?  

Frustrating but there must be a solution...

Edit: asked about swapping the 1&4 coil and 2&3 coils to address 180 degrees out cams but realized that wouldn't work 

Zaddict wrote:

Edit: asked about swapping the 1&4 coil and 2&3 coils to address 180 degrees out cams but realized that wouldn't work 

Try it.  

Is it really possible for cams to be 180 out on these bikes given that it’s a wasted spark system? Like 1&4 and 2&3 get spark at the same time, so you’re going to get spark to the cylinder at the compression stroke even if it’s 180 off…

Looking more closely at the spark I noticed it’s yellow/orange. Apparently that’s the sign of a weak ignition system (I didn’t know - people say look for spark, not look for fat blue/white spark). Will dig in there next. 

to be honest I would think if cam timing was more than even a "few teeth" out damage would occur !!

Zaddict wrote:

It cranks fine and will occasionally fire up very briefly, but I can’t get it to keep running.
 

Okay, perhaps we can get some clarification on this sentence.

How long is "very briefly"? When it does fire, does it run on all four? Does it backfire?

If it runs at all, I think we can rule out any egregious cam or ignition timing issues. You are correct the spark appears to be weak: check all ground connections and use a known good battery.

Also, try starting it in a dark room to see if the ignition wires are arcing/leaking.

Nerdy wrote:

Zaddict wrote:

It cranks fine and will occasionally fire up very briefly, but I can’t get it to keep running.

 

Okay, perhaps we can get some clarification on this sentence.

How long is "very briefly"? When it does fire, does it run on all four? Does it backfire?

 

Over maybe 4-5 straight minutes of cranking (over the course of a few hours) I'd say it ran for a total of maybe 20 seconds, but no more than 5 seconds at a time. When it would (rarely) start I scrambled to adjust the choke and idle screw to keep it alive but it would inevitably stall. 

Which grounds should I check?  The coils I assume, and the ignitor ground.  How is the engine grounded, through the motor mounts? 

Zaddict wrote:

Which grounds should I check?  The coils I assume, and the ignitor ground.  How is the engine grounded, through the motor mounts? 
 

All of them  

I'd start with the main ground from the battery to the frame. Sometimes you'll find that even if the wire appears to be good, a lot of the individual strands will have snapped and only a few are left to provide a connection. 

There are ground points in the wiring harness, one of which is attached to a coil mounting point on the Zephyrs. There is also one in the harness that attaches to a bolt on the motor. The paint/coating on the motor mounts where they contact the engine can’t be trusted as a ground path. 
You have gotten some very good advice, the only thing I might add is the reluctor wheel the ignition system uses is indexed to the crank by a very thin roll pin. If too much force is used turning the engine over by hand using the bolt on the reluctor wheel, it is easy to shear the roll pin, yet you will never know unless you remove the wheel to check. If the reluctor has spun on the crank, the ignition module will be firing the plugs out of time. 
I can also add that if the electrical system for the starter circuit is weak and the motor turns over even slightly slower than normal, my zr550 will simply not start. It has to spin fast and have a fat spark for a cold start. 
 

Well, boo. I tried swapping out ignition components and am getting a fat spark across all cylinders, but still no joy. I couldn't even get it to start at all this time. Also, I noticed quite a bit of backfiring. Actually, pretty sure my entire neighborhood noticed the backfiring as it sounded like a shotgun blast at times.
I'll go back and recheck cam timing, not sure what else to try. 
 

Did you try swopping the coil trigger wires left to right (the back firing suggests it's firing out of sequence)