Well here's the problem. My mother owns a Kawasaki Ninja 250 and it's a 1998. She bought it from a man who worked on his own motorcycles and he had customized it a bit. From what i can tell the only thing he did was put K&N Filters on it and an aftermarket Muzzy exhaust pipe. She's had it for about 3-4 years now and it ran ok up until about a year ago after it sat for quite a while. She had problems with it and left it with a mechanic for several months and he was able to get it running.
It had slight throttle issues where it would bog down at high speeds and not rev for a split second. After we got it back i started it every day with no problems for a few weeks until i got my motorcycle license last weekend. I drove it around to get an inspection with no problems in town never exceeding 45. I got it on the highway and after i hit 70 it started bogging down and would not accelerate properly or go over 50. It only got worse even after i filled up the tank until it died completely and would not idle or run what so ever.
I'm only 19 and have no professional experience with mechanics but have done a lot of self taught work on my car with success so i figured i'd give it a go on her motorcycle. After researching heavily on whatever i could find i decided to get started on cleaning parts that i was sure were unmaintained.
I took off the gas tank and checked all the hoses for cracks and wear with no problems. I then took the bottom of the carburetor apart (the bowl) and cleaned the only jet i could find which would be the main jet (the center of the carburetor).
It was slightly dirty but nothing severe. I cleaned the bowls which had a lot of residue built up, then i checked the needles which were spaced by two washers, lubed the slider around the needle very lightly with vasolene and around the vaccum gasket for a proper seal. I then changed the spark plugs and placed anti seize on the threads, changed the oil with 10w-40 street bike oil, and cleaned all the gunk off of whatever i could. I cleaned the 2 K&N air filters and the K&N oil filter below it.
I allowed ample time for the parts to dry, i replaced everything tighly and securely and started piecing it back together. It started and idled fine then i took it for a test drive only to be dissapointed. It accelerated but very poorly. It was definately bogged down but started puttering in 1st around 7,000 rpms until it kicked in and accelerated perfectly fine. Then into second fine, and then half way through 3rd until it stopped revving and bogged back down.
This was all at full/completely open throttle. Determined to fix it the next day i took it apart again and recleaned the bowls (which were still clean). I had the exact same results. So today i tried checking the gas tank and the fuel cutoff valve. I put it on reserve and the bike did perfectly fine for about 30 seconds until it started to bog down again, so i then began to take apart the fuel cutoff valve only to find it had no problems.
I then fabicated a manometer to synch the carbs which i did, they were synched to begin with, it still accelerated with an extreme bogged down feeling so i tried taking off the air filters to see if they weren't letting enough air into the carbs with only a very odd difference. With the airfilters off it would do the same thing where it only kicks it after around 7,000 rpms in first but it did it consistently whereas it would not before.
Before it would only kick in like normal once before it would cease to kick in at all. I have no idea what else i could possibly try to clean or repair and i am extremely frustrated. If anyone could please help with ideas or other parts that could effect the throttle. As it stands right now the bike idles fine first start, will not throttle properly (Is extremely bogged down no matter how much throttle you give it), and after you accelerate and slow back down it will die if your in first.

 

If anyone needs any other information i forgot to post that would help diagnose this further please let me know so i can fill in any gaps.

 

Not sure whats going on there with that bike, but welcome to the forums, someone should be on that should be able to steer you in the right direction.

 

Welcome to KF

Check and record the float heights. 2 shims under the needle? Keep that noted and at what thickness for future use since it sounds like you said air filters with the muzzy pipe. So are they K&N pods? Check for any added inline fuel filter since the P.O maintained his own ride.

 

My guess would be either boogers in the primaries or sticky floats; probably the floats hanging-up. Carbs fill with fuel, run fine through the gears until the fuel level "drops." The floats stick and it can't recover.
Like I said; just a "guess."

 

Hope this helps

 

Now here's the really confusing part. Yesterday i had not touched it all day until around 5:00pm and i started it with no problems, it revved like normal, and then i drove it around the block perfectly fine.
So i then got really excited, went inside to eat dinner, came back out and it was back to doing the same thing bogging down right when i started it for the second time.
I did note that the coolant for the engine was under the LOW line and i'm wondering it that isn't partially effecting it because i felt like it rode fine until it warmed up.
Are the floats the yellow things that are hinged in the bowls of the carburetors? If so i don't believe i checked them at all.

 

Yep. That's them.

 

I'm curious, any updates on this? Have you got the bike running yet?

I had a very similiar problem on my bike a few months back. Over the winter I had done some work on the bike and I replaced the fuel lines. I ended up using the wrong type of hose for the fuel lines that hardened over time and restricted fuel flow. At first everything was fine, then after an hour of riding it'd start hesitating and loosing power, then as time went on this interval shortened until it would take only a few minutes and eventually starter fluid to get running. I replaced the lines and have sine put over 1k miles on it without issue.

 

Well i have the bike running now, it will start and run fine for about five minutes but i think i've narrowed down the problem to uneven floats.

I never thought of replacing the fuel lines....what kind of material do they have to be? I've recheked everything though.


The fuel tank is clean, the petcock is clean, the carburetors are clean, the engine block is clean, the air filters are clean, the oil has been replaced, the choke isn't sticking, the throttle and clutch now operate smoothly. And the sparkplugs have been replaced with the proper plugs ( I gapped them myself to about .32 as this is the only setting i could find to gap them too) and they are autolites.


I did use seafoam and had the fuel tank off, carburetors open, and sprayed it directly into them and the bike would rev beautifully if i sprayed enough seafoam. I have ordered the float adjustment tool so that's my next project, to make sure the floats are at their proper levels.