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Popping on decel....

7K views 22 replies 9 participants last post by  whitehendrix 
#1 ·
I have an 09 250 and I recently put a Dan moto slip on exhaust on it. Afterwards I noticed a lot less engine braking (which is good) but also quite a lot of popping when I let off the gas. Now I know I'm probably running really lean right now seeing as I've increased air flow and not fuel intake. So my question is what would be the best way to get proper air/fuel mixture again? I've heard a little about shimming the needles, but is there a better way?


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#7 ·
do you have any other performance mods? my buddy has a 2010 250ex with the same slip on and he doesnt seem to have the popping. the back pressure could be a factor of temperature. what kind of climate are you riding in? maybe your not used to it? did you get the insert with the dan moto (the growler?) if so, his has it, and i have only heard it backfire when it hasnt been run in a while and the air is a bit on the chilly side.
 
#8 ·
I have a GP Corsa from Leo Vince and if the bike is cold or has the choke on while it is cold it does the popping noises, once the bike warms up and you remove the choke it should rarely make any noises. I use it as a way to measure when my bike is actually warmed up, well that and throttle response.
 
#9 ·
I have no other performance mods. It does it whenever I let off the throttle at any rpm, but worse the higher I am. I do not have the insert in it. It didn't come with one and I've heard ppl who have them have had problems with melting the carbon fiber because it redirects the hot exhaust fumes directly to the sides of the pipe instead if straight out. It has also backfired once when I tried to cold start it after it wasn't ran for 2 weeks.

Temp wise it does it in 90 degree weather and 30 degree weather, doesn't seem to matter.


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#10 · (Edited)
There are a couple of reasons for your issues. Basically the Dan Moto exhaust is a loud, hollow, empty can, so it is not baffling any noise like the heavily baffled stock steel can. Believe or not there is some popping on decel even with the stock can, you just can't here it.

A lot of the the popping can be controlled by not closing the throttle completely slam shut. Roll off the throttle smoothly, doing so prevents causing a lean condition which is the cause of the popping.

You may want to do the Kleen air delete mod. (removing the kleen air system) if the backfire or popping is too bad and at least shim the needles with at least 2 washers each, which will make the bike slightly richer where it is needed. Also getting the baffle for the Dan Moto exhaust will help reduce some noise. As far as the melting of the carbon fiber goes, it seems to be happening whether the baffle is inserted or not on few of the Dan Motos, most have had no problems.
 
#14 ·
How does the Kleen air mod help? Won't that cause me to be leaner than I already am?
The kleen air delete mod will not make the bike leaner. It actually removes/blocks extra air. Many have done it with positive results.

What would be the quicker/easier way to fix this? Getting the stage 2 or shimming the needles? Money wise it's not a problem, whatever would be best.
A lot of fine tuning can go into rejetting. Shimming is very simple and quick, no tuning required other than resetting the idle speed.

What all goes into installing the jet kit? I've read how to shim the needles, doesn't seem too hard although the only experience I've had with carbs is on a lawn mower. Can the jet kit be installed by myself or a shop?
Adding a jet kit will require you to remove the carbs and manipulate the airbox for clearance, which can be a PITA the first go-round. Multiple tunes and test runs are par for the course for getting the jetting correct. It's not a one size fits all deal. You or a shop can install it, but not unless the shop has done Ninja 250 re-jets before, they tend to fumble at getting all the small details of it. For a proper re-jet, the bike needs to be dynoed to find the correct setting. For just a slip on, shimming works well.
 
#15 ·
the jet kit is easy, theres a diy somewhere floating around.

if you are competent, it will be an easy task. taking the stuff off was probably more of a hassle than anything else
 
#16 ·
Just buy the jet kit, they have done all the tuning for you. Getting rid of the Kleen air system will help a lot because it is really just an air injection system to dilute the exhaust for emissions. I have not done it on my wifes Ninja yet but I have done it on my Suzuki with good results. The popping is a lean condition. So before you rejet, go buy a K&N air filter and follow the stage 2 instructions. It is easy and you will be happy with the end result.
 
#19 ·
find the diy guide, read it. if you dont think you can do it yourself, get a shop or someone else to do it.
 
#20 · (Edited)
It will be more difficult to remove the carbs then the actual re-jetting. If you can read you should have no problems :) http://www.dynojet.com/pdf/2193.pdf
Just remember, someone just like you assembled it the first time.
I have had good results with minimal tuning when the Dynojet instructions are followed. I think some people assume the instruction don't apply to their situation or they somehow know better. Dynojet ( or other jet kits) test out the product with a chasis dyno and then package it all together for you, so unless you live at some crazy altitude just follow the directions.
 
#22 ·
idk or remember about a gasket, but yes they have to come off. you have to remove and replace things from the kit.
 
#23 ·
i'm just here for the vagina. and to have my sig here since it's useful.

sometimes.
and yes thats definitely a lean afterfire, but i'll surmise you haven't dipped that far in AFR to where you're at risk for a catastrophic meltdown. theres no load on the motor. when there load and you're lean, thats when you kill things very quickly. shimming needles won't do shit for decel since the needles are still seated for the most part regardless. smaller things like taper and the sheer amount of height offset play a role in idle AFR, but thats widely controlled by float height and the mixture screws.
 
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