Inconsistent idle/off throttle surging

[Jakobi]

Well, I finally got it dialed in for the most part. The bike now runs and idles fine, but is still real lean at 0-1/4 throttle. But that is only jetting combination I have found that allows it run well across the range.

I fiddled with everything, so I can't tell you what finally made the difference. Two things that I think are the most likely:

1. When I first got the bike, the airbox was not fully seated on the carb. It was hard to see, because it was on the right side of the bike. Because my problem got worse over time, I think it may have allowed enough dust and debris into the carb that clogged the air screw. While cleaning the carb (twice) I noticed residue in the pilot screw hole.

2. Even after checking my choke cable free play and things looking okay, I noticed the cable can bind at either the handlebar or the carb. I adjusted the routing to keep slack on both ends.

After the main problem was solved I tried all kinds of needle/main/pilot combinations to dial it in and settled on what JD recommends: 180 main/38 pilot/red needle in 4th clip position. My final issue is that lean 0-1/4 throttle. This bike is extremely sensitive to needle taper and clip position. One clip change on the red needle changes a ton, so I think I will keep it on the 4th clip and add a shim under the clip.

What makes you think its lean from 0-1/4 throttle? Are you jetting hesitation? Have you tried dialling it in with the air screw?

 

[Robby45]

It's herky-jerky on the bottom and detonates quite a bit. From roadracing 2 strokes years ago- I would describe it as the "about to blow up" feel. The air screw is only about 3/4 of a turn out. I've tried a 40 pilot, but then it goes way the other way rich. Like I said, I've never seen a bike this sensitive to jetting. It's real close now though. Gotta say when it's dialed in, this motor is awesome.

 

[Jakobi]

It's herky-jerky on the bottom and detonates quite a bit. From roadracing 2 strokes years ago- I would describe it as the "about to blow up" feel. The air screw is only about 3/4 of a turn out. I've tried a 40 pilot, but then it goes way the other way rich. Like I said, I've never seen a bike this sensitive to jetting. It's real close now though. Gotta say when it's dialed in, this motor is awesome.

Right on. My personal experience was quite different where I even with a 35 pilot the bike was nice and crisp. I went with the 38 just to be safe. The 40 was torquey but loaded up and didnt idle so well, and a 42 felt way too fat.

Not sure if its been suggested, buy have you considered measuring your squish? A large clearance here can also make the jetting quite finicky.

 

[Klausen]

Stolen from elswhere

SIZE: P/NO Dia.
NOZF 13383-37EB0 2.705mm
N1EF 13383-37E60 2.705mm
N0ZE 13383-37EA0 2.695mm
N1EE 13383-37E50 2.695mm
NOZD 13383-37E90 2.685mm
N1ED STOCK NEEDLE 13383-37E40 2.685mm
N0ZC 13383-37E80 2.675mm
N1EC 13383-37E30 2.675mm
N0ZB 13383-37E70 2.665mm
N1EB 13383-37E20 2.665mm

seems to indicate f=2.705mm E=2.695mm D=2.685mm and so on...

..so
G= 2.715
H= 2.725
J= 2.735

After your info I can't imagine that the DDK needle should be comparably to the blue JD. May be to the DDM or DDL.
The diameter is to small and you got pulling over.
Now I use a
KTM needle N3EG #3
175
35

But I don't find a idle when the engine has the working temperature.
The idle die off after 1/2 minute.
The engine starts cold very good with shoke ,
but warm and half warm is not so easy.
When I use also the shoke it works.
What can I do?

The throttle response is good now not perfect.
And 300cc bike produce (1/2-1/1) very much power. For me in 3h race a little bit to much.
I already use a stronger EXHAUST VALVE SPRING .

I can also confirm that these 2009 GG 300cc with the new PWK 38 is very sensitive to the jetting.
I heard that the older model of PWK 38 with the round cap is very much easier to handle.

When I remember to the KTM 300 EXC 2005 with the PWK 36 S AG.
This model was very easy to jet.
No holes and and very good throttle response with almost every needle and jet.

 

[Klausen]

After the main problem was solved I tried all kinds of needle/main/pilot combinations to dial it in and settled on what JD recommends: 180 main/38 pilot/red needle in 4th clip position. My final issue is that lean 0-1/4 throttle. This bike is extremely sensitive to needle taper and clip position. One clip change on the red needle changes a ton, so I think I will keep it on the 4th clip and add a shim under the clip.

I can't imagine that the JD kit (200/250/300 Gas Gas jetting kit JDG001) fits for every GG model.
The old and new PWK 38/36 carbs are so different.
Or do you have different experience?

 

[Jakobi]

After your info I can't imagine that the DDK needle should be comparably to the blue JD. May be to the DDM or DDL.
The diameter is to small and you got pulling over.
Now I use a
KTM needle N3EG #3
175
35

But I don't find a idle when the engine has the working temperature.
The idle die off after 1/2 minute.
The engine starts cold very good with shoke ,
but warm and half warm is not so easy.
When I use also the shoke it works.
What can I do?

The throttle response is good now not perfect.
And 300cc bike produce (1/2-1/1) very much power. For me in 3h race a little bit to much.
I already use a stronger EXHAUST VALVE SPRING .

I can also confirm that these 2009 GG 300cc with the new PWK 38 is very sensitive to the jetting.
I heard that the older model of PWK 38 with the round cap is very much easier to handle.

When I remember to the KTM 300 EXC 2005 with the PWK 36 S AG.
This model was very easy to jet.
No holes and and very good throttle response with almost every needle and jet.

Lift the needle one more clip position and compare again.. I personally think the N3xG is still a tad too rich in the lower openings, and that the H/J needle would be all it takes to clean up the idle.
Also, have you tried to set the idle once the bike is up to temp by adjusting the idle screw and air screw. No use tuning it on a cold engine on the stand. Use the choke when starting to keep things nice and rich. Let the bike warm up. And it should settle into a nice warm idle.

I am also using the 38, N3EG#1, 175M. My bike will sometimes not idle perfectly in gear when warm but that is more due to clutch drag. Back in neutral no dramas at all. Starts 1st or 2nd kick every time. Pleanty of power on tap.