I am at 900' asl.
The bike right now:
DG muffer no insert
128 mj
35 pilot jet
3n on needle
3 turns out
Snorkel removed but kept the lid.
UNI air filter.

Right now the bike runs great except a popping on decel. I just ordered a 38 pilot jet hoping it will help. I had played with the adjusting screw but went back to 3 turns out.

Now for my question. After inspecting the plug it almost looks like it is barely running a fuzz lean. I don't know exactly how the needle works. Would it be better to go to the 132 jet or move the needle to say 4N ? Like I said I don't know exactly how that works.

Thanks.
Lenman

 

Usually removal of the pollution system will eliminate backfiring on deceleration. Take it off and plug the connecting points with rubber caps. They are at the head near the exhaust outlet, at the air box and a small vacuum connection on the outlet side of the carburetor.

 

Popping on decel isn't that unusual, the engine goes lean at higher rpm running only on the pilot circuit. You'll find if you barely crack the throttle the popping will stop, it starts to draw on the needle. I don't get too shook up with the normal stuff. Now if it really bangs, you have issues.

I will say I am running the KLX300 brass including the 40 pilot at about 2 turns out and the N1TC needle. I am at 908' with that set up. I am still running stock exhaust for now, so I may not hear popping. In the needle/needle jet/main jet I use a fuel mix adder to deal with lean jetting, so it doesn't run lean when on the needle or main.

 

After you remove the air injection system, check the exhaust for leaks, and install the larger pilot with a setting between idle drops, your pops are history..

4N will richen the midrange while the top end will remain the same, which, in your case, is apparently too lean.

The 132 will richen 3-3.5k to redline. If you go with the 132, you may be in for a pretty big surprise - the increase in power levels everywhere.. If so, there is more to be had with lid off and another jet change..

 

Thanks for the replies !

I had considered running lidless but I use mine 90% offroad and somehow we always seem to find more dust than what Oklahoma had during the great droubt. And after seeing what I had in the airbox with the snorkel still on I just didn't feel comfortable running without the lid. As it is the bike screams now. I noticed a big change with what I did do. I look forward to seeing it after this now. I will go to 132 & 38 and pull the smog stuff off. I gotta help a friend put new tires on his bike tonite and then rip into mine tomorrow. I will report back when its done.

Thanks again guys !
Lenman

 

One question I have is for the hose that comes up off the front of the motor that goes up the valve. Do you just cap that part of the valve as well or just remove the whole thing ?

Thanks

 

Very intriguing. I never looked at it like that. When I tear into tomorrow I will see how it looks after last weekends ride with just the snorkel removed.

 

With a reply like that it seems apparent you do not now nor have ever actually run off road.

The snorkel design drops air in behind and below center of the air filter, any heavier particulate or water that may enter the snorkel will tend to fall behind rather than on top the air filter. Kind of thing an off roader actually wants to happen. Plus the baffling effect will help keep the filter cleaner longer.

If it was just about a bit of dust from road riding, that would be another story. On my 650 I have the snorkel out, the lid cut, but still on due to noise. I don't ride it off road much and the amount of dust on the filter is heavy considering that I am usually the guy leading.

The 250 keeps the snorkel, but in the larger size KDX snorkel, not the small 250. Doing the math shows it is significantly larger than the throat of the carburetor and almost as large as the inlet boot to the carburetor. So odds are the flow restriction won't be too tremendous, while still offering the off road advantages.

So just how big does the opening have to be to meet the requirements of the carburetor? After looking at the dyno charts run by Marcelino in his first post, there is a max gain of about 1 hp and .5 lb-ft torque (converted from DIN hp and kg-m) at the peak, but less at many other other points in the graph. So the lid with snorkel only costs a small amount and I take it he was running the small stock snorkel, which is significantly smaller inlet size than the KDX snorkel. So close, it makes me wonder what happens when the larger snorkel is used.

In response to the proposal about dirt suspension I have a similar point with a bit of science behind it. Fact is if the particulate, water and/or dirt, would, enter the air box at a higher rate of speed it would be less likely to be drawn to the air filter - requiring a 90° turn - since it would require more force to alter the heavier particulate path to make it turn than if just sucked in through a big opening over top the filter. That is due to Newton's first and second laws of motion. The engineering that came into play when inserting snorkels into air boxes - even for off-roaders like the KDX200/220 and the KLX300 where there would be no other reason - had some sound foundation for doing so. Like channeling flow to keep particulate/liquid off of the air filter as much as possible.

When you need it off-road, you need it, thus the reason why the bigger snorkel remains in my 250.

 

Screw it, you know more than Newton, more than the dynos that Marcelino used, and apparently your 35 years trumps everyone in the world... I beg your pardon sire.

 

You can make or buy a plate to replace the entire reed valve apparatus, but I found the easiest solution was to buy a rubber cap at the local auto parts store and slip it on and clamp it. I think it was 1/2" diameter. Did the same on the airbox, but seems like it required a 5/8" cap. The vacuum line at the carburetor may be 1/8". All caps together came to something like $2.