Tweaking the carburetors

[broken neck]

Hell-O there,

I now have my Area P quiet muffler installed. I have been riding it for about a month and I noticed some "popping" sound.

First of all my current set up:
Ninja 250 2011.
Area P 18" Quiet Muffler, full system
Stock air box, but snorkel delete
K&N drop in air filter
DynoJet Stage 2 Jet Kit installed as Dynojet recommend it, clip in the 3rd
groove, main jet DJ098, 3 turns out for the mixture screws
I drilled my carburetors slides, with drill bit size #70 (0.028 in or 0.711 mm)
Kleen air system removed

Now my problems or so I think:

My throttle, when I twist it, it kind of stumble around 2k then goes up good, when I release it, the RPM doesn't seem to come back quickly but it doesn't seem to hang before coming back and it doesn't dip then come back to idle.

Then there is a popping sound around 3.5k to 4.5k, when I accelerate you can't hear it very clearly but you can feel it's there. When you have a steady throttle or if I'm cruising at those RPM, you can clearly hear the sound. When I hit 5k, everything goes back to normal and you can feel a "surge" of power.
Those conditions seems to be amplified when it's cooler or colder.

Finally, when lifting the throttle and decelerating, sometime you can hear a loud "pop", I would say a backfire.
This doesn't seem to affect the power or the comportment of the Ninjette.

Before I try anything, do you have any opinions on how to fix those little problems?

Since Dynojet didn't mention to drill the carburetors slide, can this cause the problems? If so, should I plug the holes with some kind of silicone? Or can I make up for those holes by playing with the mixture screws?

From what I've already read, my problem really seems to be my mixture screws, but I don't know if the added holes could play a part in my "popping" sounds.

Or could it be something else?

Thanks for your help.

[jkv45]

Pop the snorkel back in and take it for a spin...

or try richening the needles.

Throttle position (1/4, 1/2, 3/4, WOT) is more important that RPM as far as figuring out what needs to be adjusted.

[quarterliter]

Sounds like your running lean partial and off throttle. Raise the needle 1 clip and go out another half turn on the mixture screws

[subxero]

when jetting make note of throttle position more than rpm like other guy said. Jetting is more about the throttle position than rpm but there is some relation to rpm but it is just easier to think of the throttle position alone to start.

That being said, what size hole did you drill into your slides? the slides are very sensitive to this and you must make sure you did not drill to big of a hole.

did you change the pilot jet.... you probably should not have but you did not mention anything so just wanted to clarify.

Don't mess with your idle mixture screws until you have everything else at least some what sorted out. Put them back at 2.5 turns out and leave them there until you get the other jetting issues worked out. Use the idle adjustment knob on side to control your idle rev and get it in a good range for testing.

Ok some other things, for the the low rpm range which i generally attribute to low throttle input idle-1/2 throttle can be trouble shot with the choke. Simply let the bike warm up, then take it for a ride on say a nice straight easy 35-45mph road. Give various throttle inputs and take very particular note on what happens and how bike reacts, sound, feel ect... Then after you go through various scenarios put the choke on full and repeat all the same scenarios and pick out the difference. If bike runs better with 1/8th-1/4 throttle inputs your pilot jet is lean, if bike runs better in 1/4 - 1/2 throttle you needle is to low and lean. If sounds, bike runs worse in throttle ranges with choke on then you are to rich to begin with.
There is overlap between the jet circuits so adjusting one will have a minor effect on surrounding circuits.
Example ( my bike is running rich at WOT but runs great at 1/2 throttle so i put in a smaller main jet. Now my bike runs great at WOT but runs lean at 1/2 throttle. you would then raise the needle height and test bike again).
I personally like to jet from the main jet down. Get the main jet right as it is easiest IMO, then move to needles and you might have to go back to main jet after needles adjusted

Try and tune one circuit at a time until you get more familiar with jetting and how things interact and you can anticipate side effects.

The backfire could be an exhaust leak but that is typically on deceleration not acceleration
The other popping you describe sounds like a rich conditions to me that i have encountered in the past. Choke test should help shed light on it. Choke test does not work well for main jet tuning at WOT

[jkv45]

^ Excellent advice and tips on carb tuning procedures!

[JAG]

Maybe Your oem air filter clogged or not capable of allowing enough
Air through causing erratic throttle. As more vacuum
Created at higher speed the foam is sucked forward causing an opening
Allowing proper airflow.

[JAG]

Try New spark plugs tightened to 115 INCH LBS GAP .03-.04 inch

[broken neck]

Sorry, for the delay...

I forgot to mention that the spark plugs are new.

The air filter is also new and it's a K&N drop in kind.

I screw back in the mixture screws half a turn, the popping sound seems to be gone, I can hear more the "rumble" of the exhaust. (now 3 turns out)

I tired a quater turn more in, but the popping sound moved from 3.5 k to 4.5k to around 5.5k to 6.5k. So I put it back to my first attempt above (3 truns out).

What I've read from Vex DIY on the mixture screws, those are supposed to alter the idle to 5k RPM. Is the popping around 6k RPM means something else?

Now with 3 turns out everything seems better, but I'll try it more afterwork, when I'll be able to test it more in different gears, throttle positions, etc...

Thanks for your advices, keep them coming.

[jkv45]

You still need to think more in terms of throttle opening than RPM...

I think you need to richen the needles. Determine if there is a mixture issue at 1/4 to 1/2 throttle position. If so, make a change to the needles.

That's assuming it's running properly at WOT.

[subxero]

I don't understand how people get so hung up on the stupid idle mixture screws when jetting. They only control a very small region of the jetting. Primarily at idle obviously. If you are having problems beyond 1/4 throttle you have other jetting issues and turning the stupid idle screws will not accurately fix the issue. Perhaps they can help mask it giving you a false sense of success.