I have an 09 KLX and 4 other bikes. I make an effort to ride each at least once a week but sometimes the KLX gets negelected. I have rejetted the carb and she will now start easily if the gas has not been in tha carb for more than 10 days. Anything more than that and no start, and I keep the battery on a tender. When this occurs, without fail, if I drain the carb bowl and let new gas from the tank in she starts first try.
This has happened 10 or 12 times. I have worn out the carb drain bolt! This is the only one of my five bikes that has a carburetor and if I ever knew how to beat this problem I have forgotten. Any help?

 

Even with ethanol gas, I don't think 10 days or 2 weeks should make a carb pilot circuit or choke circuit plug up even in the high humidity of Florida. Yes, there's a point in time and environmental conditions where it will happen but not 2 weeks. On top of that, the pilot circuit is the first to clog up, but the choke circuit takes a huge amount of time to clog up. The common scenario for bad fuel in a KLX carb is that the pilot circuit clogs, but the bike will start on the choke circuit. Then as you try to transition from the choke as the bike warms, the pilot circuit will not let the bike idle. At this point you can often get the bike to run with half to full throttle because you're operating off of the main jet and needle circuit.

Since your bike won't start at all after such a short time, I'm suspecting you have one of the models that may need the choke/starter jet drilled out for improved cold starting. I would also check fuel level using the clear tube inspection method as described in the shop manual...the factory clear tube tool isn't required. A low fuel level can cause difficulty for the choke/starter jet to pick up fuel. The issue of drilling out the choke/starter jet to a slightly bigger size isn't uncommon on some bikes. Internet diagnosis can be difficult, and you could have some other problem, but this is my first guess on your situation. You mention that it starts after draining the bowl and allowing another charge of fuel to enter. That can still be a choke jet or fuel level issue. It indicates to me that your carb is right on the edge of receiving enough fuel for cold starting, and your process of refilling the float bowl is allowing it to pick up the fuel. In the short period of 10 days/2 weeks, that fuel in the bowl should still allow a cold start with the choke if that fuel is being picked up in enough quantity. It does sound like the fuel level and/or choke circuit isn't getting to the necessary level for a good cold start. Some owners have also opened the fuel petcock...not the float bowl drain screw...and tilted and shaken their bike to help the cold start...which can overcome a low fuel level.

 

Thanks for your excellent reply. Lots of good info I did not know or had forgotten. I agree it sounds like a low fuel level issue and I will check that. I seem to have misplaced my shop manual, is there a good source online for a PDF version. I assume the fuel level is adjusted by bending the float arm as I recall doing in the old days on my 72 Honda XL250. And I recall connecting a length of clear tubing to the bowl drain and the level should be at the line where the two bowl halves join or is the KLX different?

Thanks again TNC!

 

Yes, clear plastic tube like from a battery vent tube or such and bend the small float tang that touches the needle. On manuals, I'm sure someone will chime in with online sources. I still have my old paper manuals.

 

What you are experiencing is normal. Something about the bowl design and/or venting design of the CVK34 kills E10 volatility in just a matter of a few days.
If you don't want to operate the carb drain before starting, you can try the prestart "shake".. Shake the bike enough to slosh the fuel in the carb bowl, reinvigorating its' volatility, then hit the starter..

 

klxster, it's fairly clear that both you and I are nerds...LOL! Only nerds would spend this much time studying and discussing issues like this. I will differ with your take here but only slightly. You too have probably read and studied testing, theory, and real world application of the pure gasoline vs. E10 gasoline debate. The pros/cons of both...yes, there are some pros for E10...have been so beaten to death and are so full of bias that it has become very difficult to clearly ascertain fact from fiction. There are papers, intensive lab testing, actual engine dyno testing, and on, and on, and on for one to research findings, arguments, and surprising end results. I don't know exactly what your final take on E10 fuel is, but without going into fruitless detail here I will say it's not bad and maybe even pretty decent.

In a vain attempt to be brief, I will say that E10 fuel's biggest negative is its ability to absorb water. However, that is also a negative that is way overblown in the sense that it takes time and conditions for that to become a serious problem...storage methods, environmental factors, time, etc. You touch on "volatility"...and that is yet another negative of E10 in that it is slightly less volatile than pure gasoline. Volatility gets a little fuzzy when you're talking about fuel either in its natural state...as in sitting in an open container...under a mixing situation as in atomizing in a carb throat...or under compression and being ignited in a combustion chamber. At these different points in a fuel's state of being or in its state of use, some of the values, benefits, and negatives change. For example, cold starting is a tiny bit harder with E10 vs. pure gasoline. However, the octane rating of gasoline is improved with E10...this one causing frequent disbelief and denial in many cases...this usually caused by a misunderstanding of what an actual octane rating is and does...the same people who believe that higher octane fuel will always provide more power just due to a higher number.

Those comments only scratch the surface of this debate, and I want to stay on point with how this affects the carbed KLX. klxster, your volatility assessment does have some effect on cold starting, but E10 has more than enough temperature volatility within a reasonable time frame...before significant water absorption occurs...to support proper starting...IF...all other operating parameters of the engine are within spec...like valve clearances, carb fuel level, etc. Also in the case of the OP in this thread, he appears to be in Florida where cold temp starting shouldn't be a major issue. And while the usually high humidity conditions there could contribute to water absorption, two weeks shouldn't be that critical.

However, I think the bigger factor here is fuel level and/or choke inefficiency in the form of too small a choke/starter jet. In the case of the fuel level, if the level is high enough for the pilot and main jet circuit to draw adequate fuel, the engine will run and operate just fine. However, the starter jet is in the very top of the carb body as it relates to the float bowl. A low fuel level will diminish its effectiveness at cold start when engaging the choke. Now, as to that starter jet...it has been shown many times in the past on this site where slightly drilling out the choke/starter jet to about .017"-.018" will solve the cold starting problems on an otherwise fully functional KLX250. In my case and for many others, fuel level was carefully measured and set accordingly, fuel quality, air filter, valve adjustment, spark plug, and all other performance elements were in top working order, but the engine was consistently problematic for cold starting, especially when the environmental temps dropped. Simply drilling the starter jet to the prescribed size totally removed the problem.

So, do all carbed KLX's require the starter jet to be drilled for satisfactory cold starting?...No. Why is that? Hard to tell, but we all know that small, almost insignificant variables exist from engine to engine. By the same token, not all KLX's require the float bowl to be drained or the bike to be shaken or leaned over to require two week old fuel to start a cold engine. I think it does show a very marginal cold starting efficiency that is probably affected by the fuel, fuel level, start jet size, ignition system, KACR compression release, etc. The beauty, IMO, of drilling the starter jet is that you don't really hurt any other aspect of the carb's operation...as long as you don't snafu it by drilling way too large. The choke circuit only operates when you pull the plunger **** out...or engage the cable on models so equipped. Why would Kawasaki have a starter jet that is marginal for cold starting? I think it's because of emissions. Cold starting is one of the worst polluting time frames for an engine, and it's one that is usually measured for EPA standards for street legal vehicles. Having as small a starter jet as possible helps. This may or may not be the case for the KLX, but it's the one I suspect.

klxster, on our method of shaking and/or leaning the bike over to help a cold start, I think more than volatility, it affects the fuel level and/or splashing a tiny bit of fuel up to the starter jet. Shaking and especially leaning the bike over to a degree will usually raise the normal fuel level in the carb, and this assists a low fuel level and/or provides more fuel to the starter jet. Many of these KLX's are on that very edge of cold starting efficiency and nearly anything will help them get just enough fuel to spark that cold start. I know you seem to have never been a proponent of drilling the starter jet, but I will always contend that there is no real downside to doing so. It will only function when the choke plunger in engaged, and it will result in less time on the choke circuit. If one has a KLX with a CVK34 that has a proper fuel level and a drilled starter jet, that bike will start in practically in any condition and temperature if the rest of the bike's components are in order.

 

I think I understand your meaning of the word "nerd" - using knowledge through research.. I admit, I never would have taken you for such

The "repeatable ad infinitum" symptom was that the KLX would hard start after sitting for over 2 days - hard or no start when sitting longer. Also, this syndrome has been verified by other members with similar ride habits.

I had spent a great deal of effort trying to determine why the KLX suffered, what can only be described as "accelerated fuel aging", compared to my many other carb'd "toys".
"Accelerated fuel aging", because to instantly cure the problem, you simply drain the bowl a little.

Then recently, a member who was getting tired of draining his bowl a little, learned of the "prestart shake" and reported that it works !
This means that whatever is causing the problem is circumvented by introducing a small amount of additional fuel and mixing it with the fuel in the bowl - all done thru the shaking..

Barring some kind of weird design issue internally, that is "fixed" by creating a small fuel flow thru the needle seat, the only other conclusion is that since the problem is solved whenever tank fuel is introduced into the carb bowl, something must be happening to the bowl fuel (some kind of loss of volatility)..

In the end, this problem is very "real", weird, and unique to the CVK34. on our KLX's. If an experiment is ever posted ( or has been ) proving the "drilling of the starter jet" cures the problem, then this procedure should be added to the "list of cures" - but behind shaking the bike or draining a little fuel out of the bowl before starting.

 

I will try the shake method, thanks Klxster. Reminds me of laying the KLR650 on her side on the side of the road to get going again after running out of gas, lol.
I have really enjoyed reading this discussion by you two nerds, Thanks!

 

For what it's worth from a non-fuel nerd... My starter jet was drilled to I think 0.020" per Doug Pippin's recommendation - if it was 0.020" - pretty much from the word go. My brother had the drill and drilled it... could have been smaller, just guessing. But it seems my KLX starts readily with week old fuel, after a month takes a bit more effort. But my KLX650 wouldn't start if the fuel was over 5 days old. Crazy times. So with the 650 if it was a week, drained gas. With the 250 I try to see if it will fire, then drain if not.

 

For what it is worth, (non fuel nerd here as well) I have the exact experience as Kawa-Liga. Having read up on it here, I was slightly annoyed but not shocked to find that the bike would not start after about 10 days or so. Draining the fuel and allowing fresh fuel into the bowl fixes it every time, routine. In fact I have a jar with skull and crossbones on it, with a long handled allen wrench on my work bench. I feel as though I read someones post from quite a while back, that had attempted to ignite the fuel drained from the bowl and found it hard or impossible to ignite. I have only half heartedly attempted the shake method, and had no success in as far as I took it.