Hi!

I just purchased a 2007 KLX250S with a number of mods including a Muzzy exhaust & header pipe, carb drilled & shimmed, de-smogged & changed snorkel, and a K&N air filter. The P.O. jetted the bike lean to compromise between near sea level riding and Colorado. He used a FMF jetting kit and can't remember which main jet is installed. The bike "pops" a lot on de-acceleration and definitely needs to be richer. Are there any tutorials with pictures on changing jets for this bike? Do you have to remove the carb or can it be done on the bike? I live at 200 feet above sea level and will be doing a TAT trip this summer starting out at 3,000 feet and going to over 10,000. After I have the jetting correct for my home at 200 foot, how much would the jet size need to change for the trip. My plan is to change the jet before leaving home and trucking the bike to Amarillo, TX to begin the trip. The bike should never be below 3,000 feet on this trip. Thanks!

Donnie

 

Man dude, like 60% of this forum is this same exact question.. Do some searches, you'll find what you're looking for.

 

As CL suggested, there are lots of posts with specific jetting numbers for all kinds of combinations, but I would comment about a couple of your issues. I think a KLX that is perfectly jetted will still exhibit some decel popping under some conditions. No, it shouldn't sound like the first day of duck hunting season, but unless the bike is jetted overly rich, I think you'll get a little of it...especially when going down a steep grade at higher rpm or slamming the throttle shut during high rpm under a good deal of engine braking. Rather than use the decel popping as your jetting guide, read the spark plug and go by the actual performance of the bike. Does the bike stumble anywhere in the throttle range? Is the power delivery smooth and strong from off idle to wide open? Can you hear any detonation or lean pinging at any throttle position? Is your spark plug displaying a light gray or whiteish color indicating a "too lean" condition?

On jetting for altitude, I live at 1700', and my jetting, mileage, and performance were excellent from home all the way to 10,000' in the La Sal Mountains outside of Moab. The CV carb has a bit better capability of dealing with wider variations of altitude than conventional slide/needle carbs. If your bike is a little lean at near sea level but still runs well, it will only get better as you climb in elevation. The FMF jet kit should be a DJ kit actually. If so, it shouldn't need shims under the needle, as you have grooves for the needle clip to adjust.

IMO a bit of decel popping can be a sign of clean carburetion and good fuel mileage. I have almost the exact same mods on my '06 both when it was a 250 and now a 300. It ended up with the exact same jetting as a 300 as it was when a 250. Don't jet by assumption. Go by plug color and performance.

 

I know and I have read a lot of the posts! I know that I need to go one or two steps richer on the main jet. The main questions are geared more for the info such as does the carb have to be removed to change a main jet? What has to be dis-connected to remove it or position it for a jet change? Pictures are good!

Donnie

 

Thanks! I will keep that in mind. The bike is "popping" an excessive amount.

Donnie

 

Before getting to the nitty-gritty of the jetting, insure that your desmog items are completely sealed and that there is no air leak. Did the PO use a block plate for the smog equipment or just seal the reed valve assembly nipple with something? Even a tiny bit of air leakage at this point will make the bike sound like a huge popcorn machine.

 

Thanks for your response! I have the smog pump that was removed and I am having a problem locating where all on the bike the various hoses were hooked up. I think it has one connection at the air box behind the carb, from what I have read, I think it was plumbed into the exhaust system. If so, the bike has a full Muzzy system so that should be OK. Apparently there is one more area that it hooked to the crankcase, but I have not identified it. Is that correct? Three connection points? I have found a lot of threads on removing this pump, but I am having difficulty identifying the locations because the pictures do not show anymore. Thanks!

Donnie

 

My jetting is 132 and 40 and runs perfectly at my altitude of 300ft up to 2000, And as I coast down the hill from work everyday, I do get the light pop pop pop, but its never been too much of an issue, and in fact sometimes I just give the throttle a slight touch and it goes away. It actually only does it in a low gear with just the right rpm's

Hey Donnie, if I missed you somewhere, welcome to the forums.

 

Hmmm...my smog stuff has been off so long that I can't swear how many attachments there were. There's one on the airbox for the fresh air that is injected into the exhaust tract, and there's a reed valve plate on the cylinder head where the fresh air is injected. I think the carb intake manifold has a nipple that controls how/when the fresh air is drawn and injected into the reed valve. It's been awhile, so if I'm wrong, maybe someone else can clarify. You have to cap the nipple on top of the rubber carb intake manifold. You have to cap the nipple on the airbox. The cylinder head reed valve plate and hose nipple can be plugged with a block-off plate or a cap or plugged piece of hose. Many have that Bill Blue block-off plate that's a nice looking piece of work. I'd say the reed valve plate at the cylinder head has the best chance of leaking depending on how you sealed it up.

 

Thanks! I found the plug on the front/top of the cylinder head. I can see from a picture where the air box plug should be. I haven't had the seat and tank off yet. And the third and final plug should be on top of the rubber intake manifold. I will check those! I have no reason to believe there is a problem with them than as you said in an earlier post, this needs to be verified before going to a fatter jet. From what I have read a 128 jet should be about right.

Speaking of jets, I am pretty sure the P.O. has a DJ128 in the carb because the plastic bag that came with the FMF jetting kit has been remarked by the P.O. from DJ128 to 124. The kit has a DJ132 which seems awfully rich. I am at 200 feet elevation. I may need to buy a single 130 jet. I have read somewhere that someone suggested that a KEIHIN or OEM jet flowed more gas than a DJ jet of the same size. Any truth to that in you opinion? Thanks again!

Donnie