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?
2008 Ninja 250R Blue; Two Bros M series slip on, 2wheels levers, Hotbodies under tail, Sportisi tank cover
2007 GSX-R 600 Red; Two Bros M series slip on, 2wheels levers + rear sets, Vortex frame sliders, Crown Moto USA Carbon Fiber
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.
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.
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.
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.