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Discussion Starter #1
Alright well I’m gonna explain this the best I can because I’m two months of messing with this thing with no luck yet so here we go.

Bike was running when I bought it but sputtered pretty hard with loss of power in the high rpms WOT. I tweaked the carbs and got it smooth and then after a mile or so of riding down the road it started to bog hard and what felt like miss and then complete loss of power with no restart for hours until it was completely cooled off again. I’ve cleaned the carbs completely top to bottom multiple times, new plugs, synced the carbs, second trip out it had way more power but then a mile or so out it bogged out and lost all power again and won’t restart until hours later. I’ve tried every position on the a/f screws from 1.5 turns to 3.5 turns with no difference, once it hits 200 degrees it will bog out and die 10/10 times. Let it cool down completely to under 100 degrees and it will crank and run seemingly fine until it gets hot and dies again. Oil level is normal, fuel pump is new and working as it should, coolant is normal. When it is running I can spray the exhaust with water and all 4 evaporate instantly so I know they are firing but it just doesn’t want to run good or stay running. Believe it or not I can’t even find a shop in my area that is willing to work on it because no one wants to mess with these carbs so I’m stuck doing it myself. It has a cut and modified exhaust high flow slip on (attached image) and a k&n air filter. At a loss to what to do at this point short of buying a jet kit and hoping it works.
 

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Discussion Starter #3
Another thing, is there a way to tell if the carbs have a jet kit already? The caps to the a/f screws were already drilled out.
 

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there is an oring under the needle seat(held in with a screw, in the float bowl).....pull out the brass seat and replace all 4 of these orings....what are the colors of your spark plugs??
 

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Discussion Starter #5
Before I changed the plugs #3 was black like it wasn’t firing, after the first sync and clean and replaced the plugs they have all gone to a normal burn color but its still running the same and still dies once it gets hot. And will a normal carb rebuild kit have those gaskets you speak of?
 

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i'm not sure, but it should be included in the kit....not the average Oring will fit, but it does exist ...it isn't sold separately for OEM.

typically, stalling out when hot is a rich condition.....or an overheating/coolant issue piston seizing kinda mess.

does it start without the choke when cold?
 

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Discussion Starter #7
It did before the first clean and stall, but after the second clean and new plugs and an attempt at syncing them it did require choke, but the choke would make the RPMS jump pretty high after a minute and it would have to be turned almost completely off to get a good choked idle. And then again it died after about 10 minutes of operation. When I first brought it home it cranked and ran as long as it wanted and I rode it multiple times but it would also sputter and have moments of power loss when you crank open WOT but it never died on me. In the process of trying to clean that sputter up I screwed up the A/F posistion and the carb sync, the caps to my A/F screws had already been removed and I have no clue if the bike has a jet kit already so every setting I’ve adjusted to has been “factory” give or take and not for a dyno jet set up, have no clue how to tell if it has been done other than the caps being removed. After the poor attempt at cleaning up the sputter it is as it sits today, it requires choke to crank over cold, when cold it idles fine and sounds good but once it warms up it starts to gain a weed eater like idle that doesn’t sound good at all, it will start running rough and sound like it’s gasping for air and if you breathe on the throttle it will die. Once it does this it has to cool completely off to restart.
 

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Have you checked that the fuel tap / petcock is not faulty? I have seen taps fail and then effectively dump way to much fuel than is necessary (I'm assuming it's a vacuum tap).
 

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Discussion Starter #9
Not sure if that would affect this bike or not, the fuel pump only pulls gas when it needs it. If the bike is off and I take off the line from the carb that leads to the fuel pump it won’t drip a drop unless I turn the key.
 

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Good point. Have you checked the coils aren't breaking down under heat? Try heating them up with a hot air gun when running to see if they give the same result. It may not be the problem, but at least it eliminates a potential issue/cause. It could also be a blocked fuel cap breather/vent causing the fuel to 'back up'after running for a while. Sometimes it's something very simple causing the issue, but we are convinced it something more complicated.
 

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Discussion Starter #11
The bike gets so hot so quick it’s hard to say. I’ve tested the coils alone and they test on a multi meter normally and when the bike is running I can spray all 4 exhaust pipes and the water will immediately evaporate so I know it’s firing on all the coils, and the plugs are brand new. I’m still leaning towards it being a carb issue since it’s only gotten worse since messing with the carbs. Gonna try a 24 hour soak completely disassembled, a rebuild kit and a new jet kit and see what happens after that.
 

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You could try cleaning the cap vent hole. It's only a 10-minute job so no time wasted really. Much quicker than taking off and re-syncing the carbs, even with a bench sync.
 

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If you take the cap off the tank, and then take it apart you will see some (maybe one) smaill (pin size) holes. These are there to allow the petrol fumes (expanding) out and air in. If these get blocked, which is common on older bikes, they can cause fuel starvation issues. A good what to check if they are blocked is to take the bike out and after a good ride open the cap. If it makes a whooshing/wheezing sound (technical terminology) then the vent is blocked.

Hope this helps.
 

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Discussion Starter #15
The tank has made some hissing noises before but I’m not have a fuel starving problem it seems to be running too rich and flooding itself out to the point of not wanting to run. The level of fuel in the fuel filter never changes or gets low.
 

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Discussion Starter #16
Update: carbs got soaked, every inch cleaned and gone over. All O-rings are good, nothings clogged. Bench synced dead even, double checked and triple checked that it was dead even. A/f screws set to 2.5 turns out from seated. Started with choke on, wouldn’t without. Idled great until it got over 200 degrees that’s when the idle started to drop, started to pop run like shit until it ultimately cut off. Same thing that’s happened every single time. Nothing is remedying this problem. There is no mechanic willing to work on this bike near me. I will never ever waste my money on a carb bike again. No suggestion I’ve gotten on this forum has worked or made anything any better. At this point I’m thinking I might as well cut my losses because nothing is working.
 

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Don't give up. I was going to do a 'ritual fire' with my GT until I finally got it going. Some more simple things that may cause the issue.

1. Check the inlet rubbers from the carbs. If they are cracked they could be causing issues that only show up when the bike is hot (off choke, rubbers hot and cracks opening up)
2. Have you checked compression? My daughter's car was running crap, changed all usual things (coil packs, etc) to find out that compression was v.low on one cylinder.
3. I would re-check coils with a hot air gun as hairline cracks will only open up when the coils get hot.

Keep going, the joy when you fix it will outweigh all of the issues you are having now.
 

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Discussion Starter #18
Don't give up. I was going to do a 'ritual fire' with my GT until I finally got it going. Some more simple things that may cause the issue.

1. Check the inlet rubbers from the carbs. If they are cracked they could be causing issues that only show up when the bike is hot (off choke, rubbers hot and cracks opening up)
2. Have you checked compression? My daughter's car was running crap, changed all usual things (coil packs, etc) to find out that compression was v.low on one cylinder.
3. I would re-check coils with a hot air gun as hairline cracks will only open up when the coils get hot.

Keep going, the joy when you fix it will outweigh all of the issues you are having now.

By rubber inlets do you mean the intake boots the carbs sit in? My clamps for those are kind of worn out and it can be difficult to get them super tight. Could enough air be getting through the boot bypassing the carb to cause that? And I’ve tested the coils cold they checked out but not hot. Only way I’ve “tested” them hot was to spray the exhaust manifold down to see if any of them wasn’t evaporating the water instantly but they all have. I assume that you put the heat gun to them while the bike is running fairly cold still. The problem is consistent, the bike will crank over no problem at all with choke, choke will spike the revs so I cut it back, once the bike is warm and starts creeping into the 200’s it starts to run like crap and slowly looses power and bogs out and dies. The revs are smooth up until this point and at that point it starts to spit sputter and pop until death if given any gas, also sounds like is gasping for air when it does this. Today I will be checking all electrical components to make sure everything is the correct voltage and working as should. Starting to think I’m getting a weak spark when it gets hot mainly because it’s the same time every single time. If I ride the bike and keep the temp down it takes longer to happen, but while sitting still it’s like clock work. Compression test was done by a shop right before I bought it and it was within normal spec. I will update my findings on electrical later today. Check list for today is as followed

-check intake boots for air leaks
-re check for vacuum leaks
-battery, rectifier, stator, and coil testing
-go over clean air mod and stupid ram air crap
-pray to the motorcycle gods
-piss off neighbors some more because my bike is super loud ?
 

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Heat causes expansion. The ECU or the coil gets hot and expands. This expansion can separate a fine / broken circuit inside causing it to not be able to conduct the electric signal that tells the coil to spark, or it could be inside the coil and it simply can't deliver any spark even if the ECU is telling it to. In this situation, you can usually re-start the engine once it has had a chance to cool back down and it'll run just fine until it warms-up again and stalls. This is a tell-tale sign that there is a hair line fracture in the ECU's circuit or in one of the coil's windings that separates and loses connection when it gets hot and expands.


Assuming it isn't fuel related since you've gone through the carbs it comes down to air or spark.

Air intake would not be affected by temp...so that leaves spark.


I'd say start with that #3 coil you mentioned the plug being black on.
Brand new coils are not cheap...but on ebay they can be had for a relatively decent amount.
 

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Discussion Starter #20
Heat causes expansion. The ECU or the coil gets hot and expands. This expansion can separate a fine / broken circuit inside causing it to not be able to conduct the electric signal that tells the coil to spark, or it could be inside the coil and it simply can't deliver any spark even if the ECU is telling it to. In this situation, you can usually re-start the engine once it has had a chance to cool back down and it'll run just fine until it warms-up again and stalls. This is a tell-tale sign that there is a hair line fracture in the ECU's circuit or in one of the coil's windings that separates and loses connection when it gets hot and expands.


Assuming it isn't fuel related since you've gone through the carbs it comes down to air or spark.

Air intake would not be affected by temp...so that leaves spark.


I'd say start with that #3 coil you mentioned the plug being black on.
Brand new coils are not cheap...but on ebay they can be had for a relatively decent amount.
So here’s what I’ve come down to and I believe this is going to be a Fixed finally answer. But I went to check all electrical today and in doing so fully removed the tank, usually just had it sitting on the back to still supply fuel, when I hooked up my funnel to the fuel pump it clicked a few times when I turned the key but once I cranked it the pump would no longer pull. Bypassed the fuel pump straight to the crab and the bike cranked right up and runs literally perfect. 12.9vcold, 11.4v crank, 14.02v stable. Revs crisp and clean and drops back to a perfect idle everytime. It tricked me by clicking every now and then so I assumed it was working, wasn’t until I tested it for sure that I knew it was fried. Can’t believe I didn’t test that a long time ago ? Live and learn I reckon. Ordered a new fuel pump and expect to be back on the road ?? Thanks for everyone’s input, first time working on a bike I had myself convinced it was something worse.
 
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