Popping on Decel? Jetting?

[02silverpile]

Ok, Im not sure if this is in the correct place. My GF's 250ex, has a uni foam filter, Pro circuit T4 slip on, and the airbox lid is removed. I jetted the carb per the dyno jet kit instructions. However, when I come off of a short WOT burst there is lots of popping. In addition, if I place the quad up on a stand, and slowly roll through the throttle stroke you can hear faint popping. I have check the head pipe, and all is tight. Could the jetting be off a little. Its too muddy to get a long run to try and check plug chop. ( Im not sure this theory holds true on four strokes, im used to the two). I feel the jetting may be a little lean, thats why im popping. Any suggestions would help. I have tested this theory on the (ON, and RES) fuel setting just to make sure it wasnt being starved for fuel. Thanks.

[400exracer511]

sounds to me like you are too lean on the main jet....

[joshyz125]

it sounds like it's to lean to me

Personnally i'm not a fan of the jet kits, i would just get the pilots and mains from a local dealer, usually they will let you exchange them if you buy one and it's not the right size.

[GPracer2500]

Popping on decel is generally a lean pilot circuit (you mentioned you already checked for exhaust leaks--that's good). Try turning out the fuel screw 1/4 turn at a time for relief. If you get over 3 turns out bump up the pilot jet.

Popping on acceleration is probably a seperate issue. Try putting the airbox lid back on as a test. Does the condition improve or get worse? That will help tell you if your main and/or needle ciruit is lean or rich.



FWIW, in my experience Dynojet's instructions often leave the pilot circuit lean and the main circuit rich.

[Colby@C&DRacing]

You need to increase the pilot size. The jet kits don't come with pilots and try to use the fuel screw to compensate:(

[mr._bowtie]

Pull the plug and see what it looks like.. Thats the easiest way to tell what its doing. If its Black its rich, if its white or a light grey its lean... If its a medium grey or kind of tan color your about right. I would be more concerned about how it pull under acceleration rather then how it sounds once your off the throtle. A pop once your off the gas could just be unburnt fuel making it to the exhaust and then igniting and poping.

[wilkin250r]

Like GPracer said, popping on decel is generally a lean pilot.

Keep in mind that the carburetor doesn't know what RPM the engine is running at. It doesn't automatically switch from the idle circuit to the main circuit at a certain RPM. The only thing it knows is THROTTLE POSITION. This is the key.

If you are decelerating, chances are the throttle is closed, and the slide is all the way down. This means you are running on the pilot jet, even if you're at 3000rpm. So a problem in this area is fixed by adjusting the pilot jet and air screw (or is it a fuel screw on the 250EX?)

If you hear popping while slowly rolling on the throttle (let's just call it half throttle), you are running on the needle. This is adjusted using the needle clip (and more advanced, different needles with different shapes and tapers). If you are lean, you lower the clip, because this raises the needle and allows more fuel.