Crank No Start '77 KZ650 - Diagnosis help needed!

[lakshan]

Maintenance done so far:
- carbs cleaned and rebuilt (gaskets, o-rings, and fuel mix spring)
- replaced fuel lines
- replaced vacuum lines
- replaced fuel filter
- new air filters
- new battery
- new spark plugs
- new oil/filter/o-rings
- valve clearances checked
- replaced ignition points and gapped correctly
- ignition timing set
- compression test done (125 - 130 psi across)

Choke on full and battery charged up (13.5V) it cranks all day, sputters sometimes, no start. I did get it to start three times so far, but it always seems to foul the spark plugs.

Second time it started was last week. The exhaust was smokey so I adjusted the fuel mix screw to lean it out a bit. The next day it didn't start, so I checked the plugs and they either had no spark or very weak spark.

The last time I got it to start was a few days ago with brand new spark plugs. I had it just cranking until I slowly adjusted the fuel ratio richer. After a few tweaks it fired up, so my guess is this means I was previously trying when the mix was too lean.

Yesterday I tried to get it started with no luck (it just ran the day before). Today I tried using some starter fluid in the air intake to try and isolate the problem. It sputtered a bit when I sprayed but didn't actually fire up. I then noticed my carb cylinders were set really high compared to other set ups I've seen. So I dropped all four of them down to the minimum point (which left about 3-4 mm of gap). Still no start.

Finally I decided to pull/test the plugs and do a compression test. 2 of the plugs has no spark, 1 had crappy spark, and the other was grounding out. All of them were black and wet. After just one start up why are they fouling so fast? My compression test to my surprise came out great. I was worried I had to do a rebuild but looks like that's not necessary... yet.

I know black/wet fouled plugs usually means the mix is too rich, but then why won't it start without the mix being that rich? Is it possible it was coincidence that it started up when I adjusted the fuel mix screw out?

I general I've tried different choke levels, different fuel mix levels, different throttle opening levels and nothing so far. The times that it did start, the idle is jumpy. If I let it just sit, it slowly continues to drop unless I give it some throttle. If I don't give it some throttle, it'll idle lower and lower until it dies. I tried adjusting my idle screw but no matter what it eventually died ( now that I think about it, my secondary throttle cable needs replacing, so maybe even though I set the idle screw to keep the throttle open the cable has too much slack that it's not actually holding... )

Where I'm at now:

Compression : good
Ignition Timing : good
Fuel/Air mix : have set the fuel mix screw 3 full turns out and dropped the carb cylinders in an effort to increase richness
Sparks : fouled

I think that's all the information I have, does anyone have a clue as to what's going on here? And what my next step might be? I can try new spark plugs again but before I keep fouling plugs maybe I'm missing something? All I want to do is getting it started reliably and then go on to fine tuning other stuff.

Any thoughts and tips appreciated!

 

[GreyGhost]

Don't worry about fuel until you get a stable spark on all four cylinders. If the plugs aren't firing, they are wet because they didn't burn off the fuel, not because it is too rich.

 

[boyoboy]

this^ first.
you mentioned good spark on two of the four cylinders. you have two coils. hmm. maybe one coil is bad/weak? are the no spark cylinders both sharing one coil? if you swap the two coils and the good sparking changes to the other two cylinders - you will know which/if coil is bad.
Do this spark check with the plugs removed; but still attached to high tension coil wires ( i.e. plug cap wires on); leave the spark plugs threads touching on the head for grounding; this will allow you to visually check for spark.

just a hunch. easy check.

 

[lakshan]

That's a fair point, I have checked for spark by laying them on the engine like you said above. But I can't remember if both bad ones were on the same side. I will check the resistance of the coils today and see if I find anything interesting.

But, if the coil was bad would it have started at all? I did get it to start twice on brand new spark plugs each time, and all four cylinders were running because the exhaust was hot on all four. Doesn't that indicate the coils should be fine? Or is it possible it's an intermittent problem?

 

[TK4]

Recheck the timing, recheck your carburetor settings, especially float height - I don't think they're correct.
One coil fires #1&4, the other #2&3 cylinders - which cylinders are struggling ?
The spark plug caps have internal resistors that you can check with an ohmmeter.
Also check the high tension wires where they go into the plug caps - if the wires are burnt or corroded that can create abnormally high resistance.
That'll keep you busy for a while...

 

[lakshan]

That's one thing I didn't check yet, float height. I will do that next! Thanks.

I rechecked the timing and point gap so many times so I'm fairly confident timing is good. Besides float height what other carburetor settings? Already playing with fuel mix screw and I don't have an air mix screw on these carbs.

 

[TK4]

That's one thing I didn't check yet, float height. I will do that next! Thanks.

I rechecked the timing and point gap so many times so I'm fairly confident timing is good. Besides float height what other carburetor settings? Already playing with fuel mix screw and I don't have an air mix screw on these carbs.

There's an air screw on each carb but its likely got a small anti-tamper plug over it.

 

[TK4]

See parts 29 through 32 -

 

[lakshan]

See parts 29 through 32 -

Those parts are what I have and that's the fuel mix screw under the carb. Parts 42-44 is the air mix on the upper/side and it's not accessible to me from factory. As you said it's probably under a cap but if I can avoid drilling it out I will.

 

[TK4]

Those parts are what I have and that's the fuel mix screw under the carb. Parts 42-44 is the air mix on the upper/side and it's not accessible to me from factory. As you said it's probably under a cap but if I can avoid drilling it out I will.

Drill the cap off - it'll make it a lot easier to tune.

 

[theassassin]

1976? I doubt the fuel mixture screw was capped back then. What are you using for an airbox? Or have you installed individual pod filters?..... which cause many starting/tuning issues. Unsteady idle is indication of worn jet needles allowing engine to find fuel when emulsion tube is supposed to be blocked by needle at idle......or carbs could be far out of synch. Start by checking float heights and seeing if needle valves will each hold 3psi of head, which is where I've tested carbs.