KLX250S 2009

My bike run lean seems like its getting worst.

I want to tune the air fuel mixture , where I know what I'm doing.
I want a better solution than simply rejecting the carb or buying a new carb or just blindly playing with the air screw.
Really want to avoid these solutions because I don't want to risk running too lean....never really tuned a motor so I want to make sure I don't fk it up also I want to minimize the amount of times I have to keep tuning it.


Is there any way to measure my air fuel mixture?
Does the bike have an 02 sensor?
Is there tuts?

 

Break out the wallet...

 

You can by an air fuel mixture sensor & monitor. You will need to have the sensor installed in the header. I bought one & tried to use it installed after the muffler, but it didn't give accurate readings after the muffler and I got tired of messing with it. They aren't that expensive.

One thing I figured out is that unless you are running wide open throttle, your f/air mixture is really lean, the only time it richens up is when you are WOT. Since at part throttle, it is not making that much heat so you don't really need a rich f/a ratio.

 

Take it to a dyno with an exhaust gas analyzer. They can tell you whether it's rich or lean at a given rpm and you make the changes accordingly.

 

my friend works at a machine shop and they got a dyno.

...I could go to them idk... I kind of want to do it myself .. I want to learn how to tune motors .
I guess I could learn from shop workers as well.

 

header might be too small in diameter ..idk not sure how far the sensor goes into the pipe.
you think it would be more accurate on the header?

 

You do realize both seat of the pants/spark plug reading and using AFR analyzers both require the same technique. You run it, see what it does, then tear apart the carb and change jetting. Clearly AF is more accurate at the time of reading, but AF ratios are not fixed. Atmospheric conditions will affect the air/fuel mix. Not enough for general motorcycle use though. Now road racers and drag racers it is another story, working to get that 1/10th more power on a given day to win.

Either way, it is fiddling with the hard parts to get the right mix, whether using instrumentation or old school plug chops, or just doing what has worked in similar conditions for others. I will say riders have done the homework and the knowledge is out there. DPippin and some others have done it, as has KLXter. Pippin did Kawasaki/Keihin parts, KLXter does Dyno Jet. The skill is knowing when the bike is running lean or rich, AFR uses instrumentation where old school is using seat of the pants/plug reading. For road use either is good. I did the tried and true CV mods that have proven to work well, plus installing a fuel adder to compensate for leanness, allowing me to run slightly lean jetting. The fuel adder also allows for atmospheric variations where fixed jetting does not, the other reason I used it.

The choice is yours to do. I chose the route that took the least effort to be in the ball park. I had the carb off twice, mostly because I tried shimming the stock needle, but found I needed the adjustable needle. Had I done exactly what was in the mods I'd have only had it off once. More riding, less work. I did all the jetting stuff when racing on bikes where the carb was easily accessible. I don't want to have to do the same on a bike where it has to be half torn down to do the work.

But if you do want to play and learn the most, I'd say spend the money and get the AFR equipment, have the O2 sensor welded/brazed into the head pipe to do it with instrumentation. Get with KLXter and get the help to do it that way. If you want to ride, do the established mods per Pippin or KLXter and go with it. By the way adjusting the idle mix is easy. Turn the screw out until the idle starts to drop (overly rich) then, counting the turns, turn it in until the idle starts to drop (lean), then divide the turns by two and set it there. Perfect idle mix varies from hot to cold conditions, so that mid setting is the best compromise. Only EFI can keep it near perfect. If the idle mix screw is at 3 turns or more the pilot is too rich, less than 1 turn too lean (I think that is the pattern). You don't want to be over about 3 turns, because the spring that holds the screw in place may not have enough pressure to keep it from turning out further, even falling out.

Have fun with it whichever way you go.

 

I found the kouba fuel mixture screw to be a very convenient item when tuning as its easily accessible which is nice especially when the engine is hot. Decel popping is also one issue that can be tuned out. Increasing pilot jet to 38 helped but a 40 was better here in so cal. Cured the cold hard starting and warming up is easier as well. Mileage came to 40-45 mpg which is fine.

 

I had a small engine for my go kart and I messed it up terribly by messing with the fuel screw. Of course I had no idea what I was doing at the time ... and the engine was significantly aged and un maintained.
But its enough to scare me out of messing with the KLX's screw.

Honestly speaking ...not out of laziness ...I want an "easy solution". Even if it takes a lot of effort , I just want to easily stabilize the ratio.
If I were to drill out the screw plug the I would want the O2 sensor so I could adjust it with some knowledge of the affects .

It sounds like you were able to adjust the jets without over richening it , i wouldn't mind swapping them but honestly I got to understand carbs more ... I. really don't have a good understanding of how they work.

 

decel pop is my main problem
pops when I rolling down a hill and sometimes pops on flat ground
never up hill and sometimes when Im just rolling.
I know a lot of bikes do it ..dont mind if other people like it but personally I really don't like it
...to me its like a dehydrated person trying to run a 10 mile marathon with only 10 of those tiny paper cups
(those cups people use to serve medicine in or for ketchup), 1 for each mile..it will keep you alive
but you'll be damn dry & thirsty by the end .

not sure how accurate or overly exaggerated that analogy is but thats how I feel



I wonder how living in a more hilly environment affects my engine..
I wouldn't think the engine is build for "hill driving" ..I live in San Francisco btw.