What's wrong with my Ninja 250R?
December 31, 2011 1:21 PM   Subscribe

my 2008 kawasaki ninja 250R isn't running right. hoping someone might have an idea as to what's going on with it.

i left around an hour ago to run an errand and decided to take my bike as it's in the mid 60's today which is a bit uncharacteristic here in virginia. i rode a couple of miles and made a brief stop, and realized after getting back on the road that i needed to get gas. i ended up stopping at a gas station i haven't been to before (having ridden maybe 3-4 miles in all at this point). i picked up nozzle for diesel gas, somehow not realizing that there were 2 seperate nozzles. of course since i was pressing the regular unleaded button, it wasn't pumping anything. after picking up the correct nozzle and pressing the regular unleaded button again, it pumped as expected and i filled my bike up. while my bike had ridden fine to that point, it felt very sluggish when i attempted to accelerate after pulling out of the gas station lot. i think i had used very little choke to that point but i engaged it fully at that point and the bike seemed to accelerate okay to about 30-40 mph at which point it just ceased to accelerate and was clearly revving really high, which seemed to suggest to me that it was adequately warmed up. when i disengaged the choke though, the acceleration was again exceedingly sluggish, if existent at all.

the only thing that seemed to have any impact was fully engaging the choke, but again, the bike seemed to be revving much too high as it would if it was already warmed up. if i turned the choke off or it was engaged anything less than completely, the acceleration got very sluggish again.

the real kicker came when i realized that fully engaging the choke and then accelerating, the bike would get up to around 30-35 mph and then seemed to stop accelerating, and when i released or rolled off the thottle at that point, the speedometer would maintain at that speed as if the throttle was still rolled on. everything really just felt wrong about it so i ended up turning back. i haven't ever experienced a stuck throttle prior to this so i'm not sure if the throttle itself should be sticking or if it's just the motor, but again, the throttle felt as though it rolled off fine, but the engine definitely maintained. this only seemed to happen with the choke fully engaged.

the other caveat is that i just returned from a week-long vacation, so the bike had been sitting in the cold on basically a nearly empty tank for the last week. i'm not sure if that's a factor however, as the bike felt perfect prior to filling the tank. is it possible that some residual drops from the diesel nozzle mixed with an entire tank of regular unleaded could have this effect? i definitely didn't pump any diesel fuel into the tank, but the problems started immediately after i refueled, and i'm just really thrown by the fact that the bike was maintaining its speed even after i let off the thottle, and i'm not sure if it was just maintaining or if it was actually technically accelerating, since the bike wouldn't seem to go more than 30-40 mph in the first place.

sorry for the long post; just trying to be as thorough as possible. many, many thanks for any insights.
posted by austere to Travel & Transportation (12 answers total) 3 users marked this as a favorite
It sounds like possibly bad gas (water in the tank or bad gas from the pump).. I know my old carb-powered Ducati did *not* like bad gas, and would run sluggish.. however, the '08 Ninja is obviously fuel-injected so I don't know what it would act like on bad fuel..

Regardless your description of the throttle and acceleration don't make sense. When you say "seemed to stop accelerating" did your speed stop increasing or not?? I don't understand how you couldn't know this for sure (look at the speedometer). Also, it sounds to me like you are claiming that rolling off the throttle didn't cause the bike to slow down - that's exactly my experience when driving with the choke on, which should be expected to some extent. I've heard of people using their choke as a sort of cruise-control of sorts.
posted by mbatch at 1:46 PM on December 31, 2011

Assuming this is the US version of the 250R/EX250J, it sounds like the fuel coming into the carbs. Gunk in the carbs from sitting, rust/crud sitting in the tank, or something else might have clogged one or more jets.

A 'drop' of diesel won't cause it. Based on the immediate result after refueling, my suspicion is that you got some gunk in the near-empty tank, or rust, or condensation that filling up to the top mixed into the fuel.

If it is just a bunch of condensation, I'd try Stabil in the maintenance amount to see if it helps. Next step would be to drain the tank entirely, drain the carbs, and fill with new gas treated with stabil. After that, I'd clean the carbs.
posted by graftole at 1:51 PM on December 31, 2011

"stuff" in the gas clogging something?
posted by infini at 1:52 PM on December 31, 2011

How was it running before you stopped for gas?
posted by workerant at 1:53 PM on December 31, 2011

the '08 Ninja is obviously fuel-injected

Nope. Carbs.
posted by mollymayhem at 1:54 PM on December 31, 2011

some possibilities that I can think of:

1) Some varnish (what is leftover from evaporated gas) or a particle of rust has clogged the jets. before you start taking things apart, buy a thing of fuel system cleaner and dump it in the tank. you may need to take the carbs off and clean out the jets though.

2) intake/vacuum leak. there are some rubber parts that provide an air-tight connection between the carb and the intake port on the head. if these get old or cold they can crack and cause the engine to run poorly. an easy way to check if this is the case is to start the engine and spray some wd-40 or propane from an unlit torch (or other flammable that won't eat rubber) in the area of the carb/head connection. If the problem is a leak, the engine will speed up.
posted by ArgentCorvid at 3:23 PM on December 31, 2011

Since it was running fine before the fill up it is likely (though not certain) that is the problem. Could be stirred up sediment/rust in the tank caused by sitting for a while without fuel in it. This usually takes a season or two stored in a wet enviroment (like outside under a trap) with an empty tank but you never know. I would start with sediment in the tank. The fuel petcock has a strainer on it that extends into the tank that can get clogged. It is really easy to take off. First undo the fuel line going to the carbs and drain the tank. If the fuel flows readily from this the problem is in the carbs not the tank, if the fuel is just barely coming out it is a tank problem. If so drain the tank all the way through this hose, take off petcock and clean. after this look in tank, and a quick safety note-its gas, dont smoke, no open flame, I would even use an exposed heating element nearby, and check for rust. If it is rusty get a new tank. If it isn't your lucky and you used up your karma for the week. If it flows ok might as well drain all the gas and put in good new gas and see if it runs. If it does see the karma comment above. If the tank flow is ok and still runs like crap you get to rebuild your carbs. It isn't hard, but it is tedious and you need a manual a carb rebuild kit and a digital camera to take photoes of stuff before you dismantle it so you can put it back together. Do this and hope for the best. If none of this works you should take to a mechanic. This are pretty basic simply bikes and a good mechanic will be able to diagnose. If it isn't the fuel Could be spark plug (not a bad idea to check anyway), ignitor, stator, ignition module, camshaft timing...a lot of things.
posted by bartonlong at 3:53 PM on December 31, 2011

My favorite is Sea Foam added to the gas. It does clean out varnish. It won't do any thing if you've got particulate in your carbs. I run 70's Honda's and use this stuff twice a year or if a bike has been idle for a while.
posted by Pecantree at 5:33 PM on December 31, 2011

Response by poster: with the choke fully on, the bike accelerated fine up to 30-35 and wouldn't accelerate past that. i'll likely have it checked out professionally in the very near future. i don't really have the time or work area to do any real maintenance myself.

also for what it's worth, the bike is pretty well maintenanced and generally ridden two or three times a week. and prior to the refuel it felt perfect. there was a total change in performance immediately upon filling the tank. but like i said, it did sit for a week with the tank just about empty.

thanks again everyone.
posted by austere at 10:03 PM on December 31, 2011

Best answer: It's possible you need to clean your carbs (don't worry it's not hard). But try this, and see if it gets you going again for now.

A few caveats: one, turn off your gas petcock, two, turn off the ignition, three make sure you're in a well ventilated area, four, don't have flame or sparks around.

1. Find the drain on the carb float bowl. It'll be a screw or bolt on the bottom of you carb somewhere that when you open it, gas will run out. Open it and let gas run out.

2. Find the gas line to your carb, it'll run from the tank to the carb, unhook it and make a mental note of where it goes.

3. Buy a can of spray carb cleaner, and stick the little red pipe into the barb where you removed the gas line from the tank and spray it until it runs clear out of the drain bowl where you removed/loosened the screw/bolt.

4. Now put hoses back and tighten screws (gently) and turn on the petcock and make sure you have no leaks. Leaking gas is bad and will make your next ride far more interesting.

5. Now put a can of SeaFoam or Marine StaBil in your tank and off you go. If it works: yay! You now can wait a while before you take your carbs apart (but you will be doing it sometime soon, be warned). If it still does the same annoying trick, do the following at some point over the next few cold and wet months: Rebuild the carbs, and change the plugs.

Now for the why: If it runs with your choke open, but not otherwise, it's because your carbs are running "lean." If they're clogged up with debris (probable because you ran the bike on the very tail end of a old tank of gas) or varnish or water or a combination of the bunch. You can verify leanness by pulling your plugs and the porcelain will be a light grey to white, instead of the nice tan they should be. Now my quick method may dislodge your debris/varnish/wet, but if the carbs have not been thoroughly cleaned in the past four years, it's time to take them apart and get all the little bits out.

A bonus: buy an inline fuel filter ($5 from your local bike shop) and you can stretch the carb cleaning out to a few more seasons, before you have to do it again.
posted by 1f2frfbf at 1:27 PM on January 1, 2012 [1 favorite]

That's right on the money, 1f2frfbf! This is definitely a fuel blockage problem. Your carb is only getting enough fuel to run the engine when totally choked out.

Here's a pic of your petcock.

It looks like it has two filters. One for the "on" position and another for "reserve". Since it does have two filters I'd try running it on the reserve position, or back and forth with the cap off to see if anything changes. (Cap off to check for vapor lock which isn't likely, but possible.) If not I'd clean the carb out run the procedures as 1f2frfbf describes.

In any case, this isn't a big problem and shouldn't cost much if you have it fixed by a mechanic.

Good luck!
posted by snsranch at 2:09 PM on January 1, 2012

A clarification upon rereading: in step three, spray the carb cleaner directly into the carb, not the fuel line. Just so you know.
posted by 1f2frfbf at 8:23 AM on January 2, 2012

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