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Discussion Starter #1
I'm going to be riding my brothers 1993 Ninja 500 for the summer. I rode it last weekend, and am going to bring it home this week.

Heres the deal:

It has a leaky tank/petcock which has been dripping gas down the fairing for a couple of months (eating the paint). It ran fine and was not leaking in March when he rode it last. I rode it on Saturday (my first time on a street bike) and I thought it ran ok having never ridden it before (or a multi cylindered bike, for that matter.

After getting used to it a bit, I noticed it starts to pull really well and smooth after about 8000 rpm. untill 8k, it seems rough and powerless. If I roll on the throttle at 3k, it is rough untill 8k, where it seems to catch (almost like I turned the choke off or something) and start to "scream".

I didn't notice this at first, since I was getting accustomed to riding again, but now I am sure there is something wrong. I was wondering if the leaky petcock has something to do with it. I havent looked at it yet, but the guy at the motorcycle shop said it was vacuum controlled. I have no idea how it works, but it seems that this would be fuel or vacuum related. I tried searching the posts but could not find this question answered. Also, the bike starts and idles fine.

Thanks in advance for any help :(
 

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A leaky petcock could cause that problem, You might wanna just take it apart and clean it up with some B-12 chemtool or other carb cleaner and put it all back together and see if it fixes the problem. If not you might wanna replace the entire petcock, or at least rebuild it. The kawi dealership or a www.bikebandit.com should be able to find the parts you need.
 

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Discussion Starter #3
Is there a chance that this is vacuum related?

The bike seems to run real well from 8k-redline

I'll take it apart when I can, it is leaking pretty bad. I ordered all the rubber parts from the m/c shop including the vacuum diaphram, but its going to be Monday before they come in.
 

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Discussion Starter #5
All right, I took a better look at it the other day. I found:

The o ring seal between the petcock and the tank was leaking.

the petcock had been gutted, and the diaphram cover was RTVed back on, with a vacuum cap on the cover and on the intake/carb vacuum source. The cap on the carb was cracked pretty bad, so I guess it was a pretty good vacuum leak.

I replaced the o ring, recapped the carb, cleaned the petcock with carb cleaner, and RTVed it back together (still waiting on the petcock parts from the dealer, Monday, I hope). I also replaced the plugs.

The bike runs a lot smoother, but the power still comes on real hard at 6-7k. Since the petcock is still gutted, is there a chance the float bowls are getting flooded or something?

Thanks
 

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it could be an issue with the carbs, but if the bike is still all stock then quite likely its not supposed to really hit the power curve till 6-7K
 

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Discussion Starter #7
installed the new diaphram and petcock rubber parts last night. Ran a new vacuum line to the carb. The bike runs a lot smoother on the low end. I can now feel the stumble a little better. When the rpms get to 5-6k in full throttle the bike bucks a bit before it clears out and pulls strong to redline.

So I guess this is a midrange stumble?
 

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PETCOCK

I'd say to change the spark plugs. Once you have a problem like you had it is almost always wise just to replace them. Also you may find tha tyour carb floats may need to be adjusted, but I'd take it in and see if they can sync the carbs, after replacing the plugs to check that first. If it isn't a sync problem they I'd think that perhaps you have a float sticking or a needle valve not seating properly...try the plugs first...
 

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If you don't have vacuum gauges, don't take it in to have the carbs sync'd and pay the money. You seem savvy enough to do it your self. Get yourself a motion pro carb sync kit for around 50.00.

Here is a great carb tuner and the website shows how easy it is.

http://www.carbtune.com/

I purchased one of these and in 20 minutes I had my carbs humming nice.
 

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Discussion Starter #10
Well, its been 2 months and 1000 miles since my last post. Heres the deal:
My buddy and I pulled the carbs and cleaned them out. They seemed pretty clean, but there was a little bit of gunk on the mixture screw from one of the carbs. We put everything back together (with the mixture screws turned 2 turns out). We didnt mess with the float levels, but he checked to see if they were "level" which is "the way he was taught". He is a stubborn *******, and wouldn't consider the method that the Clymer manual suggested (the plastic hose on the bowl way)

Anyway, the bike runs a lot better than it used to. It seems a little boggy less than 4500 rpm or so (feels rich to me, might just be the normal twin vibration). It still starts easy, and runs great at high rpms.

The problem I have is that there is a consistant stumble right at 6k rpm. It is smooth above or below 6k, but as the tach sweeps over 6k (any throttle position) there is a slight miss or hesitation. I can cruse at 6k with no miss, but it comes back if I accelerate. It botheres me because I hit it all the time on the highway.

Any idea what could be causing this? I can elaborate if it helps.

Thanks!
 

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Did you Sync

Did you sync the carbs? You may indeed find that the float level is off, causing the stumble when accelerating. You may want to try running some fuel cleaner (seafoam) through your fuel system. and check for vacuum leaks from the tank to the carbs. I know that had fnally used some Sea Foam and finnaly discovered some spider like lines in my fuel line...seems hte rubber hose had some very small dry rot cracks that I never noticed before. Now I have all plastic and fuel clamps on every connection includig my now inline fuel filter. I was trying to ride up a very steep ramp the other day and I stalled the bike. Seems that the floats don't like it when the bike is climbing almost straight up. Quick thinking, clutch and front brake let me back down the ramp. I made it the second time because I used a faster initial speed and nearly coasted to the top. Flats can be fairly sensative...
 

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Discussion Starter #12
There is a new twist to my problem.

I changed the plugs the other day, and took the bike for a 10 minute (fairly hard) ride. When I got back, I saw that there were dirt/mud drops splattered all over the pipes, so I licked my thumb and wiped at them to see if they would wash off easily. When I did that, it sounded like I touched a hot frying pan and I could feel the spit boil. So, I spit on the pipe, and it boiled and danced around when it hit the pipe. I then walked around to the other side and spit on that pipe, and the spit just bubbled a bit

So, is that cylinder running real lean, or real rich (fuel burning in the pipe)?

What can be causing it? I just had the carbs apart and they looked fine (all the jets were clear)

Is there an adjustment other than the mixture screw? (I have them set at 2 1/4 turns out)

Does the Mixture screw affect all RPMS or just the idle/low speed?

Thanks
 

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z289t6 said:
1. So, I spit on the pipe, and it boiled and danced around when it hit the pipe. I then walked around to the other side and spit on that pipe, and the spit just bubbled a bit

2.Does the Mixture screw affect all RPMS or just the idle/low speed?
1. could be a couple things.

A. sounds like the PILOT JET is still clogged on that cylinder. easy way to check that is , PULL THE CHOKE ON A BIT at idle and see if that pipe heats up. also rev the bike and see if that pipe gets hot (not to 10,000rpm just like 2,000rpm) if it gets hot doing either of these things then you have a clogged idle circuit. you may get lucky and its just a clogged PILOT JET but it may be INSIDE the carb body and youll have to let it soak after your REMOVE ALL RUBBER/PLASTIC parts from that carb (basically a COMPLETE tear down)

B. your float height it still wrong, tell your buddy to take a hike and do it the correct way w/ the manual (if all else fails, READ THE INSTRUCTIONS)

2. the mixture screws affect mostly idle but have a role in all RPMS
 

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hey not sure if this helps but i have a 90 ex500 ( my bike also has some carb problems.. can only get it to idel properly at 2000rpm) but my bike really starts to pull at 8000rpm so i think thats where this bikes power band starts..
 

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hmm

Teh hesitation sounds more like a fuel/air problem///the heating problem...how long has it been since the valve adjustments??? Just a thought that could save a burnt valve and or worse...even the air/fuel mixture if you were running to lean could burn things up...
 
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