Experts, what jets for my bike?

[FastFast]

I'm looking for some opinions and ideas to try out while jetting my bike. I know we have some really good tuners on here and I'd like to pick your brains a bit.

2013 XC300 Completely Stock and New.
50:1 w/ Amsoil Interceptor and fresh 93 octane
3000ft to 6000ft riding elevation
I have a JD Jetting Kit JDG002 at my disposal plus a few other jets in between.

 

[thejackrabbit]

make sure the power valve tension is adjusted before digging deeper too

 

[FastFast]

I still can't tune out the blubbering just in the first few millimetres of throttle. Currently on a 38 pilot, red needle second clip from the top, and a 160 main. Air screw is out about 1.5 - 1.75 turns which seems to be ideal. I've tried all needle positions, 40 and 42 pilots, and all manor of air screw adjustment without success, usually worse actually. With the current settings this bike makes great power all over, excellent transition, torque, and response. No pinging, little smoke, starts right up, chokes great, decent idle too. I just can't get rid of the blubbering just off idle and it's driving me nuts. Bike is new, no motor mods.

 

[djroggen]

160 seems lean try a 175 or 178.

 

[djroggen]

I have a 200 I bought, and couldn't figure out why it would fall on it's face when cracking the throttle from idle. I found a 145 in the main! Put a 172 and it fixed it for me.

 

[desertgasser300]

Check float height also.

 

[Jakobi]

NUMBER ONE!! Set the float height..

JD Red is about the same diameter as a H in the OEM range of needles. You'll see most people are using J diameters on their 300s with good success. That puts you 2 steps leaner right in the 1/8th throttle range. Key reason why JD kits can get you close, but can't get you all the way.

The other consideration is the squish clearance. Many have chased their tales with jetting before having the head done. It really is the best bang for buck mod you can do. I believe that so much so that I had the head off my 2013 model after one short ride (which was only to see how it ran stock).

 

[rosco]

That's close to the same elevations that we are running here. In the summer we run a 172 main, n3ch or n3cj needle in the 2nd clip position and a 40 pilot. In the winter we bump the main to a 175 and lower the clip to the 3rd position and bump the pilot to a 42. I have found that temperature and humidity have a lot more affect on jetting than elevation does.
Another thing that really plays a part on jetting is your air filter oil. I remember back 30 years ago when I was working at a local Honda dealer you could always tell the guys that were using the old Bel-Ray filter oil. Most guys just used motor oil back then so if you switched to the Bel-Ray filter oil you had to drop the jetting or else your bike ran like crap.

 

[FastFast]

I'll start by setting the float level. What is the spec? Do I need to remove the air box to get the carb out, or is there enough flex in the rubber to pull it free?

Regarding the main jet suggestions, this problem I'm having is JUST off idle when rolling in slowly. Everywhere else in the throttle the bike is spot on. Isn't that fuel circuit controlled by the pilot and air screw? Or is there some overlap from all circuits which a main jet change could effect?

 

[Jakobi]

The overlap on the main is minimal in the area we are discussing.

Float level is stickied in this section of the forum - http://www.gasgasrider.org/forum/showthread.php?t=11886 - Set it around 8mm to compensate for the angle it leans forward at in the chasis. Stock should be 6.5mm

Best access to the needle and gets is by removing the tank, removing the cap and slide. You can then roll the carb to access pilots and mains with the clamps loosened. To remove the whole carb I find the process much easier to pull the silencer/pipe (either will work), loosen the upper subframe bolts, and undo the lower ones. Swing the whole deal up and out of the way. Much less tiring than wrestling in a confined space.

 

[FastFast]

Thanks, I'll try this and post up my results.

 

[FastFast]

Some updates. I set up the bike today using the specs listed by Rossco, since we're only a couple hundred feet different in altitude and are around the same temperatures too. 172 main, 40 pilot, and a NEDW needle on 2nd clip. This made the bike nearly useless. It made almost no power everywhere and just ran like junk aside from a great idle. It still had the jerky just off idle stutter I've been chasing. So I went all the way up to a 180 main, and all the way back down to a 160 main with nearly every clip position in between. The bike runs best on what seems to be much too small of a main in comparison to everyone else.

I ran out of time working on the bike and left it at a 40p (great starting and idle) the NEDW needle on clip 2, and a 160 main. There's some pinging in the first part of the needle and the top end is a bit weak. I'll try a 165 main and see if that takes care of it. Of course the off idle stumble is still there no matter the pilot adjustment or number or needle type or poisiton. On the JD kit running a 38 pilot, red needle on the 2nd clip, and a 160 main produced the best power so far, aside from that off idle stutter.

The whole reason I've been playing with the jetting is because of the off idle stutter. It's not the pilot or it's adjustment, it's not the JD needle or NEDW either. I'm almost leaning to it being a slide issue. It's just in the first few millimetres of cable travel. Very frustrating. The only adjustment I haven't done is the float height. But is there real evidence that could be the cause this condition? Grrr hahaha

 

[desertgasser300]

Some updates. I set up the bike today using the specs listed by Rossco, since we're only a couple hundred feet different in altitude and are around the same temperatures too. 172 main, 40 pilot, and a NEDW needle on 2nd clip. This made the bike nearly useless. It made almost no power everywhere and just ran like junk aside from a great idle. It still had the jerky just off idle stutter I've been chasing. So I went all the way up to a 180 main, and all the way back down to a 160 main with nearly every clip position in between. The bike runs best on what seems to be much too small of a main in comparison to everyone else.

I ran out of time working on the bike and left it at a 40p (great starting and idle) the NEDW needle on clip 2, and a 160 main. There's some pinging in the first part of the needle and the top end is a bit weak. I'll try a 165 main and see if that takes care of it. Of course the off idle stumble is still there no matter the pilot adjustment or number or needle type or poisiton. On the JD kit running a 38 pilot, red needle on the 2nd clip, and a 160 main produced the best power so far, aside from that off idle stutter.

The whole reason I've been playing with the jetting is because of the off idle stutter. It's not the pilot or it's adjustment, it's not the JD needle or NEDW either. I'm almost leaning to it being a slide issue. It's just in the first few millimetres of cable travel. Very frustrating. The only adjustment I haven't done is the float height. But is there real evidence that could be the cause this condition? Grrr hahaha

I havent read this entire thread, but have you checked your float height? That was the first thing I did to my bike before jetting.

 

[Jakobi]

Float height is crucial.

More things to check. Confirm you have a 38mm carb, and double check which slide you are running and if it has a notch in the bottom edge or not.

 

[FastFast]

38mm carb, and it's a 7 slide with no notch. I still have yet to adjust the float.

I really want to enjoy that NEDW needle!