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Discussion Starter · #1 ·
Hello! I have a problem with my ZX6R J2 2001, I've been in 3 services and nobody can't solve the problem. Basically, sometimes when bike is cold and I use choke, the engine is turning few times and form time to time it's makes a loud bang and a nice blue flame comes from exhaust. Bike start and run perfectly but this problem drive me crazy. I am running an K&N air filter, aftermarket exhaust, iridium spark plugs, mixtures screws are set at 3.5 turns out, jet needle are set on the third notch from the top, balanced carburetors 2 times in different service, with the pair valve system blocked or opened is doing the same, i don't know what to do or what to check anymore. 馃う
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Tough to determine if it's spark or fuel. Can you attach a timing light, and next time watch the flashing of the timing light
while cold starting with choke? If it happens then, does the timing light flash consistently, or does it miss a few?

If the spark proves consistent in all conditions, then can you afford to send your carbs to an Expert carb rebuilder?
Also take a look at the entire intake tract: manifolds sealing at the head, no major cracks, carbs fit snugly in carb manifolds;
air box boots fit nicely at carbs and airbox. Airbox does not leak, and K&N filter fits properly, etc.

Some of these really high performance motors can be a little finicky
with any problems in the intake flow tract, even minor defects.

And by the way, that's a pretty sharp looking ride, cheers!
 

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Discussion Starter · #3 ·
Tough to determine if it's spark or fuel. Can you attach a timing light, and next time watch the flashing of the timing light
while cold starting with choke? If it happens then, does the timing light flash consistently, or does it miss a few?

If the spark proves consistent in all conditions, then can you afford to send your carbs to an Expert carb rebuilder?
Also take a look at the entire intake tract: manifolds sealing at the head, no major cracks, carbs fit snugly in carb manifolds;
air box boots fit nicely at carbs and airbox. Airbox does not leak, and K&N filter fits properly, etc.

Some of these really high performance motors can be a little finicky
with any problems in the intake flow tract, even minor defects.

And by the way, that's a pretty sharp looking ride, cheers!
Thank you!
Carbs are spotless, only 8.200 genuine miles with two owners and full service history. Carb manifolds are fine, no cracks, no leaking, tested with brake cleaner and there's no leaks. It's doing like that with normal and iridium sparkplug, with OEM and K&N air filter. Is doing like that maybe 2-3 times in a month. In service they tried everything, lots of different setups on carbs, even with original exhaust and OEM air filter mounted is doing like that and I can hear a small puff from the exhaust. Valve clearance was check at 8000 mile and all of them are in spec. Doesn't bother me doing that from time to time but I know something is not right and I start to have enough with spending money on mechanics and still doing like that.
 

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So, has anyone else witnessed the problem, or is it too intermittent? Maybe it's your imagination? haha, just kidding!

You said: "the engine is turning few times and form time to time it's makes a loud bang and a nice blue flame comes from exhaust"
Let's get a little more detail. What do you mean by "engine is turning few times"?
Could be: starter turns motor a few revolutions, then bang, then blue flame, then what? OR starter turns motor, engine starts after 3 seconds, revs to ?? rpm's then bang, blue flame.

The only thing I would check on the carbs would be the float levels and I would use
the dynamic method using an external tube, and if they're high, I would lower them.


So, the problem with intermittent stuff is you can't figure it out until it happens, and when it does you don't have any diagnostic equipment hooked up to give a clue to the problem.
In these cases, you either 1. keep guessing about stuff or 2. you try to make it worse!

1. If it's electrical, you can guess and try at least the following: every connection; all coils; all pickups; battery; ignition switch; right switch...you can see how
difficult it gets, and expensive; one time I bought an entire motorcycle and swapped parts side by side until I solved it, then sold the
2d bike for parts; owner of the shop where I worked said I was crazy, but I was the only mechanic who could fix it, right?

2. Make it worse: so, cold start with choke, probably can't get the choke to open any further, but you can get it colder. Wait for coldest day, work outside, set up two fans about 8-10 feet away (simulates cold wind); connect timing light or ignition tester, and give it a try, or several tries, late evening after sunset. See if it sparks every time the rotor passes the pickup.

Sure sounds like ignition to me; doesn't spark or weak spark at first, meanwhile, engine pulls
a bunch of gas into the cylinder, then something warms up and sends a spark, and Bang!
 

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Discussion Starter · #5 ·
Could be: starter turns motor a few revolutions, then bang, then blue flame, then what?
Yes, exactly like that.
Main switch on, choke lever on half, push the start button, the engine is doing few revolutions, i have the bang in exhaust, and then the engine start right away.
It's happening in seconds after I push the start button. It happens when I don't use bike for few days, if I use it regularly from time to time doesn't make like that. If I don't used for 1-2 weeks then I have a big chance to have the bang in exhaust.
I found out that lots of people have this problem but ai read al topics an nobody was able to identify the problem.
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"It happens when I don't use bike for few days, if I use it regularly from time to time doesn't make like that.
If I don't used for 1-2 weeks then I have a big chance to have the bang in exhaust."

Okay so what I said is still a possibility: "Sure sounds like ignition to me; doesn't spark or weak spark at first, meanwhile, engine pulls
a bunch of gas into the cylinder, then something warms up and sends a spark, and Bang!" and you can follow my diagnostic routine outlined above, if you want to.

OR

Sure sounds like fuel to me. The time spent without running allows the fuel in those tiny enclosed float bowls to go stale, you spin the motor, the initial charge is too stale to fire, then some fresh fuel gets in, bang! and engine starts. How to trouble shoot "stale fuel" theory? 1. Wait two weeks, drain float bowls, turn on key, let fuel pump run long enough to fill bowls with fresh fuel from tank, push starter button. 2. Take a look at fuel additives like Stabil or Seafoam, find one that ignites well. When they first came out with fuel stabilizers, they caused hard starting when taken out of storage because the stabilizer wouldn't burn as well as fresh gasoline, but I think they've improved the formula since then; worth asking a few experts which stabilizer allows easy starting at the end of winter storage. So, find that product and add to gas tank, keep tank 2/3 full, and keep a journal every 2 weeks see how it goes.
 

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Discussion Starter · #7 ·
"It happens when I don't use bike for few days, if I use it regularly from time to time doesn't make like that.
If I don't used for 1-2 weeks then I have a big chance to have the bang in exhaust."

Okay so what I said is still a possibility: "Sure sounds like ignition to me; doesn't spark or weak spark at first, meanwhile, engine pulls
a bunch of gas into the cylinder, then something warms up and sends a spark, and Bang!" and you can follow my diagnostic routine outlined above, if you want to.

OR

Sure sounds like fuel to me. The time spent without running allows the fuel in those tiny enclosed float bowls to go stale, you spin the motor, the initial charge is too stale to fire, then some fresh fuel gets in, bang! and engine starts. How to trouble shoot "stale fuel" theory? 1. Wait two weeks, drain float bowls, turn on key, let fuel pump run long enough to fill bowls with fresh fuel from tank, push starter button. 2. Take a look at fuel additives like Stabil or Seafoam, find one that ignites well. When they first came out with fuel stabilizers, they caused hard starting when taken out of storage because the stabilizer wouldn't burn as well as fresh gasoline, but I think they've improved the formula since then; worth asking a few experts which stabilizer allows easy starting at the end of winter storage. So, find that product and add to gas tank, keep tank 2/3 full, and keep a journal every 2 weeks see how it goes.
So... last night I took bike for a ride, it was sitting for around 5 days. I had that bang on exhaust when I start bike. I've been out for around 60 miles, I've stop at Petrol station, fill up the tank with 14 liters of fresh premium E95. In the morning I had some business in tow center, i took my phone out and start recording first star in the morning, everything was fine. After few hours hanging around in town, the engine was cold (8掳C outside temperature), had another bang in exhaust, small one but quite noise. I was thinking will not do that and I didn't record it. 馃う

Fuel pump doesn't work without starting the engine or engine running, i bet is something to do with the air/fuel mixed ratio. I've tried different settings, idle mixture screws set at 2, 2.5, 3, 3.5 turns, jet needles set at 2-3-4, pair valve sistem blocked or opened, OEM filter and aftermarket, iridium and normal spark plugs all of them brand new, ignition coils checked at cold and hot, all the plugs cleaned with contact cleaner. Nothing resolved this problem plus another one which is about lots of pop and bags during deceleration between 7000-5000 rpm.
 

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Sorry we couldn't resolve it here on the Forum, but it sounds like you're enjoying the bike enough;
maybe at some point you'll consider a new or newer bike, perhaps another Kawasaki,
or maybe Honda or Yamaha, some folks think they're more reliable.
Best of luck.
 

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I'm with @haybaler on this. I also think it's fuel related. It sounds like you have a dynojet kit installed. I'm not 100% sure that is problem. But, I do know that everyone that I've met running a DJ kit in their bike, runs rich and their bike also pops on start up and midrange accelerations.
 

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Kinda hard to read some of this, but from what im picking up it sounds to me like ur getting fuel in the exhaust system. Either its too lean to fire up right away so its pumping it thru, or maybe its just loading up a cylinder while it sits. Then it pushes the raw fuel into the exhaust, where it ignites w the first flame front that comes out of a cylinder. Very well could b fuel level simply too high and a less than 100% float needle. So when it sits, 1 of the carbs is letting the fuel in the line drain thru it and into the intake/cylinder. Easy way to figure out which 1 would b to pull the exhaust off and stick a piece of cardboard in the way. After u let it sit long enough to have the problem, crank it over and shut it off. See if there is fuel from any of the exhaust ports spattered on the cardboard
If nothing else u can waste sometime checking things before u decide its not worth fixing since its not causing any real problems
 

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Discussion Starter · #11 ·
Kinda hard to read some of this, but from what im picking up it sounds to me like ur getting fuel in the exhaust system. Either its too lean to fire up right away so its pumping it thru, or maybe its just loading up a cylinder while it sits. Then it pushes the raw fuel into the exhaust, where it ignites w the first flame front that comes out of a cylinder. Very well could b fuel level simply too high and a less than 100% float needle. So when it sits, 1 of the carbs is letting the fuel in the line drain thru it and into the intake/cylinder. Easy way to figure out which 1 would b to pull the exhaust off and stick a piece of cardboard in the way. After u let it sit long enough to have the problem, crank it over and shut it off. See if there is fuel from any of the exhaust ports spattered on the cardboard
If nothing else u can waste sometime checking things before u decide its not worth fixing since its not causing any real problems
For the moment I've stop doing something with the bike, i had this wonderful virus and I couldn't be bother to anything.
This year when I bought the bike, floating needles was changed because the bike was sitting in the garage unused for around 10 years and I put new Kawasaki OEM float needles, set the float height 7mm and 20.5mm fuel level. Maybe tomorrow if I feel better I will start the bike to see how is doing, is sitting for around 10 days.
 
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