So I bought a 2009 KLX a couple of days ago. The previous owner told me he tried messing with the jetting multiple times but couldn't get it perfect and that it's running rich. The bike pops a lot on decel, and when I checked the sparkplug it was black, which I find odd. I swapped in a new sparkplug and will take a look at it once I put some miles on the bike.

The bike hesitates in when ripping the throttle mid-way while cold, it loses power for half a second then kicks back in.

The previous owner has done the following:

- Removed snorkel
- FMF Q4 with spark arrestor
-Twin air filter
- No clue what he did with the mixture screw
- Idle screw is set at 2k RPM. I tried dropping it to stock settings (1.3k), but she wouldn't star a anything below 2k.
- Dynojet kit (not sure which one he has installed)

I'm also looking into buying an extended fuel/air mixture screw so I can tinker with the carb. However the koubalink ones are out of stock. Any other screws available out there? Preferably in Canada as well, since shipping form the US gets expensive.

I guess my basic question is, what do I do now and where do I start? I've never messed with jetting before, but am fairly mechanically inclined (did the doo-hickey on my KLR650, valve adjustments, fork seals...etc.)

 

Either Dyno Jet with KLXster or the jetting established long ago in dpippin's web site using Kawasaki Kiehin parts click here. Go to the carb modifications and continuation page.

Brother and I did the pippin jetting, plug and play on his 06 and my 09. Once apart and back together and go. May not be perfection, but not had any problems. No richness or leanness noticeable over about 8 years now. Lot of riders here have worked with KLXster using Dyno Jet kit parts. Either way is far better than stock.

As for popping on less restrictive exhausts like the FMF read this click here and rest assured if it is just the overrun crackle it is not a problem, in fact quite normal as the people who make Mikuni carbs point out.

 

There is no telling what all is wrong with your carb. There are many "things" the previous owner could have screwed up...

You will eventually fix it - how long all this takes is dependent upon how long it takes you to become a "CVK Guy" - able to identify every component, its' function, and know when each component has been modified from stock..

Study Study study - my link below on CVK issues, exploded views of the CVK, etc etc etc...

Once done, you should be able to determine what's wrong ( without loosing/leaving carb parts on the shop floor or down the sink drain...) ..
Or at the very least, you'll be able to ask (me) "proper" questions about fueling circuits and components.

About the fuel screw, unless yours is damaged ( by the previous owner) there is no reason to replace it - all it does is control fueling for idle and certain engine ops when throttle is just off idle (below 1/4). Also, the idle and starting issue MUST be solved - air leak and/or nonfunctional pilot fueling system.. A 2k idle is being fueled by the primary fueling system and NOT the idle(pilot) system ( which is responsible for fueling idle..)

Hope you bought it cheap...

P.S. Don't forget the simple stuff - air leaks, carb canted to left or right, improper fuel level in the bowl, improper routing of the carb's hoses..

 

Thanks for the quick response. I guess my intention of replacing the pilot screw was to have an extended one I can fiddle with without loosening the carb to access it with a screwdriver. I ordered the koubalink extended screw and that should arrive in a couple of weeks (it was expensive getting form the US ). I haven't messed with the carb at all yet, since I'm waiting for the extended screw to arrive. I'm hoping it's a simple fix that can be resolved with the pilot screw. The previous owner has the stage 2 dynojet kit on it and all the other correct mods.

The previous owner has pretty much followed all the instructions here in terms of jetting (FMF Q4, removed snorkel, stage 2 dynojet, stock header) with the pilot screw setting being the only unknown left. Which leads me to believe that the reason it's acting up is improper pilot screw setting. If it's not that, then I'll move on with my troubleshooting to more complex/sinister issues.

As for the 2k idle, what do you reckon that is caused by? Is it the pilot screw being turned too far in, hence restricting fuel?

I bought it for a fair price given covid and all (equivalent to 3k USD). It had a 2.7 gal gas tank, FMF exhaust and a bunch of other upgrades that I liked, but it's definitely been beat up. It was lady driven, but maintained by a supposedly mechanically inclined husband.

 

Hmmm, so I decided to check the fuel mixture screw before I went to work. Apparently the previous owner had it closed all the way lol. I don't understand how the bike was running at that point. I turned it back (counterclockwise) 3 turns as per the dynojet instructions. I set the idle speed at 1.3k rpm. The bike still doesn't start when hot without the increase in RPM, I compensated in giving it some throttle while turning it on.

I took it for a spin around the block and noticed the hesitation that I used to feel initially when cranking the throttle was gone. The decel pops are still there. I guess it still needs some tuning, but at least I'm getting there.

A couple of questions for the more experienced members:

1- I'm assuming the decel pops mean that the bike is running lean, and since I'm maxed out on the recommended 3 turns I'll need to increase the fuel mixture through a bigger needle? (my altitude is 3600ft)

2- Can someone please explain to my low IQ brain how the bike even ran with the mixture fuel screw completely shut?

3- Why does the bike still not start while hot without cracking the throttle?

 

1. Mikuni Backfires in Exhaust click here, same for all carb and even some EFI vehicles. One less problem.
2. The idle opens the butterfly slightly, probably was open enough to allow just enough fuel mix to run. If I remember right, some MX bikes back in the 80s or 90s didn't have any idle circuit at all.

Might still be lean on the pilot jet as well. Not part of the Dyno Jet stuff, but the old school pre-Dyno Jet guys slightly opened the starter jet, a fixed jet in the carb, care must be taken if done. I have I believe the 40 pilot and the .020" starter jet and my 250 starts no problem hot or cold. The drilling is covered in d pippin's KLX250 site click here.

 

1. Decel pops: If the air injection system is still installed and functional, popping is to be expected and is NOT indicative of "wrong" fueling. Otherwise, if the system has been removed and properly capped off, popping is caused by decel fueling being too lean . A larger pilot jet is called for. ( the #40 is a guaranteed cure )..

2. The bike ran because the idle speed throttle stop screw was turned so far out of whack ( resulting in a 2k "idle") that the primary fueling circuit was fueling the bike - as the pilot fueling circuit ( whose job it is, is to fuel idle ) was totally shut down via the fuel screw.

3. An improperly done MCM mod causes loss of hot starting. Ask the previous owner if he monkey'd with the MCM ( Cam Retiming ) mod. If so, the fix is easy. If not, and idle is perfectly smooth at 1.3k, the ignition system is first on the list. Coils, plugs, and plug wires that are on their way out, falter when hot and seem fine when cold.

 

So I finally got adound to taking the carb out. The bowl was squeeky clean but ghe pilot jet had a green tint to it. Cleaned it with carb cleaner and now she starts very easily It was giving me a lot of trouble starting on the trai.

Apparently it has a dynojet 120 main and the stoc #35 pilot.

Mt elevation is 3,600 ft and I usually get to 5,000 on ny trails. I'll keep the jet as is for now and id I feel the need to I'll bump up to a 124.

Thank you all foe the help!k