Popping on decel?

[Kahuna]

I just took the choke out of my EX, and wow, a lot more power!

Now it pops pretty good on decel if you are high in the revs.

I used to know how to jet a 4stroke then I got my 2-stroke andyou jet it different than a thumper, so what does popping decel mean?

I think it means that it is lean, but which part needs to be adjusted?

Their isn't any bogging or anything like that under acceleration, just pops on decel.

[GPracer2500]

Mild, occasional popping on closed throttle decel is somewhat normal for a properly jetted pilot circuit (especially when decel'ing from high rpm) on most carbureted engines. Excessive popping is a sign of a lean pilot circuit.

Try turning out your fuel screw a half turn or so and see if that provides relief.

Bear in mind that decel popping is NOT an ideal way to jet the pilot circuit. Popping can be an indicator of what's going on but there are other, more accurate methods for making sure the pilot circuit is correct.



Popping does indicate lean misfires. But carburetors have a natural tendency to go temporarily lean under the high vaccum signals of closed throttle decel. This is a fundmental deficency in the way carbs work. Decel popping does not necessarily mean that the pilot circuit is lean under acceleration--and it's under acceleration that it's important to have the circuit metering fuel correctly. In other words, the pilot circuit meters a different amount of fuel under closed throttle decel than it does when accelerating with something less than about 1/4 throttle. And the latter is the important part to get right.

[dariusld]

If you messed with your header pipe at all, popping is also a sign of an exhaust leak. Not saying thats it, but something to think of.

[400exrider707]

Originally posted by GPracer2500


Try turning out your fuel screw a half turn or so and see if that provides relief.



On a 4-stroke its an air screw is it not? Good info none the less.

[GPracer2500]

Originally posted by 400exrider707
On a 4-stroke its an air screw is it not? Good info none the less.

Other way around.

[GPracer2500]

Originally posted by dariusld
If you messed with your header pipe at all, popping is also a sign of an exhaust leak. Not saying thats it, but something to think of.

Thanks for mentioning this. You can run yourself ragged messing with the pilot circuit if an exhaust leak is actually the problem.

[Quadtrax]

Originally posted by 400exrider707
On a 4-stroke its an air screw is it not? Good info none the less.

It is possible for a four-stroke to have an air screw. Many vintage thumpers used two-stroke carbs? and thus have air screws. Here is how you can tell if the carburetor has a fuel mixture or air mixture screw. (1) Look at the carburetor from the side that has the mixture screw on it. (2) Draw an imaginary line down the carb's slide to visually split the carburetor into two. (3) If the screw is located on the airbox side of the carburetor, it is an air screw. (4) If the screw is situated on the engine side of the carburetor, it is a fuel screw.



It is just that simple. First thing to check on a popping on decel is air leak in exhaust. It will also be the esiest fix.

[Quadtrax]

Also ... Considering that most of racing takes place while you're on the gas (and thus on the carburetor's needle and main jet circuits), the fuel mixture circuit might seem to be of little importance. Au contraire. It is very important (even though it comes into play off idle). If the fuel mixture is mis-adjusted, your bike will run rough and stumble across the whole range. The adjustment of this circuit is so crucial that there are both external and internal ways to tune it. Under the slide. The secondary carburetor starts at that little hole pointing straight back from the bottom behind the slide. These holes channel air into the fuel mixture circuit where it is mixed with gas. This circuit controls how the bike runs off idle and into the midrange. It's adjusted by the fuel mixture screw?a tapered needle that opens or closes the flow of mixed air and gas.

[Kahuna]

It just started doing it when I took the choke out.

Now I finally got my good gas in it. (93 octane)

It stumbles if you punch it from idle, and it also smokes a whitish black color around 1/2 throttle. This is with it in nuetral, I can't ride at the moment cause it's raining.

So I'm thinking, a little leaner on the needle and a little more fuel on the pilot?