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Discussion Starter #1
Evening all.

Ok, this has me scratching my head now

Throwing this out there as chatting sometimes makes you see what you are missing !
I done a full cosmetic restoration on this bike earlier this year. (Including powder coating the frame)

The bike is a Z550GT, which I know you didn't have in the states, but basically its a Z550 with a shaft.
Electrical architecture is basically the same as the GPz550 A series, which obviously you did have.
Same CDI and pulsing coils, same interlocks and such.

I finished the build stage back in July, but with other things and poor health I hadn't got to the startup and snagging till this week.
It won't even attempt to fire, which I half expected, and started the trouble shooting.
This is where it gets weird !!

Carbs were always a question, so I took the carbs (same carbs) off my other bike that runs spot on, and fitted them over to the GT.
Cranks, not an attempt to fire still.

Coils were exchanged with my running bike, even though I had spark on all four plugs out of the bike.
Cranks, not an attempt to fire still.

Compression's are about 160 psi on all four.

Motor has not been stripped, so I have no reason to suspect the base timing is incorrect, as it was a runner when stored.

So, I have a known good fuel system, spark at the plugs, OK compression, clean good fuel supply into the carbs, but it will not even attempt a fire !!

Cranking voltage across the battery is 10V, with the same at the coils. A bit lower than I would like, but should be enough to make it go !
Battery voltage less 0.2V at the coils ignition on only compared to the battery.

Earth harness was a bit rough, so exchanged with another I had. Earth points cleaned again. Resistance from frame to battery negative under 0.5 ohms.
I can't see it being any of the interlocks as I have a spark, so I ruled them out at the moment.

I thought I had a volt drop through the cut-off switch, so fitted a donor with no change.

So to summarise, good running carbs, spark, compression, but not even attempting a fire.
Am I going mad here ????
Any thoughts please


Andy
 

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Spray a little starter fluid in the intake to see if it will fire. If it doesn't, it probably isn't getting fuel. You say it has spark. If you remove the spark plugs and ground the body of the plugs do you see spark.

I had a dead cylinder in my old ZN700 when I bought it. I verified spark to the plug but didn't verify the plug was firing and this stumped me for a while.
 

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Discussion Starter #3
Spray a little starter fluid in the intake to see if it will fire. If it doesn't, it probably isn't getting fuel. You say it has spark. If you remove the spark plugs and ground the body of the plugs do you see spark.

I had a dead cylinder in my old ZN700 when I bought it. I verified spark to the plug but didn't verify the plug was firing and this stumped me for a while.
Yes mate, squirted some carb cleaner around as that's all I had to hand, and no change.
Plugs were removed from the head and fitted to the caps again for spark testing.

Andy
 

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What do you mean by Cranking Volts across the battery is 10 Volts?....battery should read at least 12.6 VDC when not running.....and even this is not absolute proof is good.
 

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He means when he pushes the start button & the starter motor turns, the voltage drops to about 10 VDC. A voltage drop when cranking would be normal & I think a drop to about 10+ VDC would be expected under load from a starter motor. I would use a digital multimeter to see exactly what the voltages are.

Andy 01: Are you using the choke?
 

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Discussion Starter #6
Sorry, I'm an auto electrician and its easy to slip into trade speak.
Martin is spot on with his explanation, the voltage across the battery on crank is about 10V on my Avo, and the same at the coils as I initially suspected low cranking voltage at the coils.
Yes, choke is on :)

A couple of questions were raised today.
Did you have the air filter connected ?
Answer, No !
I know with these TK CV carbs they run rough with no air box connected, but I would have expected it to start al least ??

Have I removed and inspected the intake stub rubbers ?
Again, no, but leaks at that point would have to be quite severe wouldn't they to prevent the thing even starting ??

Plugs were not as wet with fuel as I would have expected, but I have a perfectly setup good bank of carbs on it, with good clean fuel supply into them.
Engine has not been apart since was last running, so base timing can't be out in reality, so why are the plugs not as wet as I would expect ?
I think this has got to be the key to this personally ??

Andy
 

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I would install the airbox with stock air filter. Without that, it's going to be lean. USA models were jetted lean from the factory for EPA regs, so without the air filter it's going to be more so. Plus the airbox provides a stable air intake environment which can be critical for CV carburetors. I would also charge the battery with a good motorcycle smart charger & do a load test. I'm not certain how much the voltage should drop with the starter engaged. The problem probably isn't the battery, but I still like to make sure it isn't something as simple as that. Troubleshooting isn't my forte, so I check & verify the easy stuff first.
 

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With 160 psig compression, verified that the spark plugs are sparking, and starter fluid sprayed into the carbs, it has to start I would think. I can understand why it's driving you crazy!
 

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Discussion Starter #9
Well, thanks for all the thoughts.
I stripped the intake stubs off as I had a spare hour this afternoon.
Really didn't like the look of it, and I suspect I'm drawing air between the stubs and the head, so not getting a good vacuum pull through the carbs to pick up the fuel.
I'm going to did deeper along that thought for the moment :)
41317
41318
 

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Hi Andy, if you need replacement intake rubbers let me know. I bought some for my GPz550H2 and purchased the later ones like yours by mistake. They have only been on my bike once and are essentially NOS. I have some new o-rings as well. Ping me if you are interested.

Regarding your no start, might be worth checking your ignition advance/retard. Mine was seized and needed a little lubrication. This may help. Also check the fuel flows, vacuum to fuel tap and the aluminium pipes that feed fuel between CV carbs these can fur up depending upon age.

cheers jon
 

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I would be suspicious of the battery,at times all the tests can appear normal,and the battery can still be bad. You will have to have it load tested,most auto parts stores can do this for you. Do you have a strong blue spark? If it is more orange you have weak spark,and under compression it may not be firing. If everything checks out,try push starting it. I would try that before I went to the trouble of taking the battery to have it tested. That way all of the battery's power goes to the ignition and doesn't have to also turn the starter. I have seen this work more times than I can remember. If you haven't I suggest replacing the spark plugs. Good Luck you will figure it out.
 

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:)I realize I am late to the party, but I had a very similar problem with my 1981 KZ550C. Cranked and cranked but would not fire. In my case, I already had it running well, then it just quit. Turned out to be the IC igniter. I popped a new one in....fired right up again.
 
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