2014 Gas Gas 300 - Jetting

[n_green]

Speaking with the tuner about my dilemma, unfortunately he hasn't had a 2014 bike engine apart yet so can't tell me if there are any difference in the crank case design from 2012/2013 that would cause my jetting requirements to be so different (although I note that I am currently using the same jetting as Simmo and whilst he raves about the jetting and gets good economy I am burbly and rich and using lots more fuel).

One thing he did suggest though is to compare the CDI units from '13 to '14 and see if they are different as apparently sometimes the curve of the ignition can cause the bike to appear rich in a certain area.

Looking at part #'s - the 2012 and 2013 (e start) bikes use part# ME250634007, 2013 racing uses part# EE511003013CT; 2014 racing/e-start bike uses part# EE51100GG-CAB-1.

So it looks like the '14 does indeed use a different CDI....

 

[Jakobi]

Interesting. I checked the CDI between the 2010 and 2013 model and different part numbers too, which is no surprise as the 2013 uses a smaller one of some other brand (not kokusan). I should swap them to see if its the notable difference.

I have a Husaberg TE300 here which I believe is using ktm SX CDI too. I could make a project out of this. As a side note, its frustrating how easily the other brand are to tune. One needle change and a few tweaks on a pilot and its running as good as any other. Guess the GG isn't much different. On another side note - I forgot how much burlier the bikes are off the bottom with an extra 50cc! What a beast!

 

[n_green]

Is the one on your '13 a small square red thing a bit smaller then a cigarette packet and mounted under the fuel tank above the spark coil?
If so it's probably the same as mine, GG have just changed part numbers for it maybe?

 

[Jakobi]

I got a little black one!

Mounted under the tank on the frame spar. The plastic plate which its mounted on is obviously for a kokusan as this one only takes up about half of it.

 

[n_green]

40p, NECJ#3, 168m. AS 1.5.

Went for a ride today, 15 deg C, 75-80% humidity, 300m elevation. Different area to where I usually ride, 10% fire/twin trail, 80% 2nd/3rd gear tight single trail and 10% techy creek beds/climbs.

Idle is good as usual, I opened the as up from 1.25 to 1.5 to try and clean up the off idle burble, there is the slightest hesitation/bog when cracking the throttle WOT from idle, but if rolled on quickly it's not present. It's also undetectable when under load accelerating out of corners.

The burble I've come to know and hate it ever present from off idle to just before 1/8. From here it starts slowly clearing up and from half throttle it's great.

The 168 main has made a big difference in the top end. The 172 was good, this is a lot better. Noticeably crisper and pulls a lot harder.

Here's where I get confused. If when in 3rd/4th or higher and I roll along at idle then crack the throttle WOT, it pulls straight away and smoothly until roughly 1/4 rpm range where it seems to lose a bit of power and not pull as hard. It's only brief but noticeable. Only lasts a fraction of a second and then it picks up and pulls hard all the way through to flat out. Trying to replicate this in 1st or 2nd doesn't do it, must pull through that part of the rev range too quick.

At first I thought maybe it was a lean hesitation, and maybe it is, but there are no other signs of it being lean anywhere. No pinging, running on, bogging, definitely not snappy. There were several times today when I was in that part of the rev range slipping the clutch working the bike up hills and it never appeared lean.

So I'm running with the theory it's a rich hesitation and now that I'm running a smaller main it's made it more noticeable when it clears out coming onto the pipe. The plan is to drop the needle a clip and see if it gets better or worse.

Fuel use for today was 6.2l for 64ks = 9.8l/100ks. So the economy is better too. Still room for improvement I think.

 

[Jakobi]

Jetting is throttle position related, and has very little to do with rpm. I'd be more inclined to say that your dip in power may be either the power valve opening either too soon, or too late.

 

[n_green]

Jetting is throttle position related, and has very little to do with rpm. I'd be more inclined to say that your dip in power may be either the power valve opening either too soon, or too late.

I realise this but didn't want to confuse the explanation, when this occurs the throttle position is WOT, I was just trying to explain where in the rev range it occurs each time. If that makes sense.

The PV does make a bit of sense, I may have to get the bike going and determine when it is opening. The PV opening time IS dependent on RPM isn't it? Which means the '14 with its very basic trail tech unit and no tacho won't tell me much.

Having said that why is it so noticeable now?

I may be putting this thing on a dyno yet...

 

[Jakobi]

Indeed!

The governor works off the centrifical forces created by the revs building. At a certain point the force will overcome any preload on the PV spring, and then open at a certain rate.

Speak with Dave re some options. I know he has run some data on the PV in the past and I've seen his graphical representations of the dip in the power curve which happens when the PV isn't timed well. At a guess I would say its likely remaining closed a touch too long, falling out of its efficiency, and then as it opens it comes back onto song.

It may be a case where its only noticable going from low rpm at wide throttle. Generally if riding you'll be up in the revs where the PV is either on the verge of opening/part open/open, or working in the lower rpm before it comes on. The taller gears will highlight its behaviour as its happening over a longer time frame.

 

[n_green]

Indeed!

The governor works off the centrifical forces created by the revs building. At a certain point the force will overcome any preload on the PV spring, and then open at a certain rate.

Speak with Dave re some options. I know he has run some data on the PV in the past and I've seen his graphical representations of the dip in the power curve which happens when the PV isn't timed well. At a guess I would say its likely remaining closed a touch too long, falling out of its efficiency, and then as it opens it comes back onto song.

It may be a case where its only noticable going from low rpm at wide throttle. Generally if riding you'll be up in the revs where the PV is either on the verge of opening/part open/open, or working in the lower rpm before it comes on. The taller gears will highlight its behaviour as its happening over a longer time frame.

He touched on this the other day actually, mentioned that the Gassers do benefit a lot from work on the PV spring. Hmm the new clutch side cover from the '15 with the adjustable PV mechanism should fit straight onto my bike..... I wonder if the PV governor itself is the same?

And you are right, it is only noticeable in the taller gears when WOT from low RPM. The more I think about it the more I agree with you it is more likely pure PV related.

In any case as mentioned, I'm still rich off the bottom, so I'll drop the needle to clip 2. Last time I did this was with a 172 main and boy did it get snappy at 1/4 throttle so I'm expecting that to happen again, if it does I'll go halfway and run NEDJ #2.

 

[wa_ndro]

i was just looking at powervalves myself and found this link on the site regarding shimming the spring...

http://forums.everything2stroke.com/threads/45719-Pics-exhaust-valve-system

 

[n_green]

Looks like this is my only real option. Had a look at the parts fiche tonight, as well as needing to buy the main clutch side cover it looks like the new bikes use a completely different governor assembly and linkage arm assembly which would cost a fortune to purchase.

 

[Jakobi]

I'm starting to see the benefit in having access to a spring tester. Anyone know any local shops (non industry related) which would also use them?

I've seen the variance in tolerances/lengths/rates in most other springs. By nature there will always be some variance in them. I do wonder how much though. I haven't had the pri cover off my 2013 yet, but I know my 2010 had no shims in it.

 

[n_green]

Changed the needle to NEDJ#2, kept 40p, AS 1.3 turns out. 168m.

Rode 100ks on the weekend. 50ks day 1 of super techy/tight single. Very slippery terrain lots of slick off camber root infested trails. Mainly 1st/2nd gears.
50ks day 2 of mostly flowing single, 2nd/3rd gear with some top gear wot runs.

Idle is fine as usual, air screw has noticeable effect on idle.

Off idle still noticeably rich. Burbles and 4 strokes at anything less then 1/8 throttle. Well and truly cleaned up by 1/4 throttle and it's superb from here on.

Pulls super hard from 1/4 throttle. Flattens off right at the very end of the rpm range but I suppose that's normal and I never usually rev it that hard anyway.

Can still feel the hesitation just before it comes on the pipe but it doesn't seem to be as obvious as when I was using the NECJ#3.

The hunt to lean out the bottom end a tad more continues.

Fuel economy - not sure but somewhere between 10.5-11.5l used for the 100ks.

 

[n_green]

http://youtu.be/UXj2z42NgmU?list=UUjfBPCXhd98OBZkBtBnp99A

 

[n_green]

So bored this afternoon I got the verniers and compared some straight sections of various needles. What I did was work out where the straight section ends and mark it with a texta. Clearly not scientifically accurate but visually it paints a picture, especially when I compare same tapers/different diameters:

First up is G diameter needles:
From L to R: N1EG, N3EG, NECG, JD BLUE.


Next is W diameter:
L to R: NECW, N3CW, JD RED.


Next is W and G diameters:
NE, N3, JD.
The W dia is on the left the G on the right.


Next after Jakes suggestion we have the W and G diameters again, but this time I have also marked the G diameter on the W needle. It is the lower of the two marks.
NE, N3:

For giggles I got my NECG,H,W,J needles and did the same. Marked the end of their respective straight sections and then also marked where the G diameter would be on them:

Like I said not scientifically accurate but visually it's obvious the straight section on the richer diameter needles is longer then the leaner counterpart.

I found it interesting anyway haha.

 

[Jakobi]

For comparison, you should also do a crude check of the diameter between the needles where the richer one first starts into the first taper. Like last picture, where you have marked the rich ones should be a G diameter, then at the same point measure the W (which will be on the taper) and see how closely they match.

 

[n_green]

Good idea.

 

[n_green]

See above, I edited the post to include the comparison images as per Jakes idea.

It looks to me that there is no doubt the needles all run the same taper from the tip upwards. As you can see the mark for the 'G' diameter is in the same spot on all needles in the same series. And as can be seen especially in the NE needle photo each step leaner on the needle results in a minutely decreased straight section length.

It's hurting my brain trying to think about this but here is what I think the results could mean:

The 'J' diameter needle with its slightly shorter straight section would be on the taper slightly before the 'G' diameter needle is. In theory this means that the 'G' diameter needle should be leaner at part throttle openings then the 'J' diameter needle due to the slide being able to open more whilst still on the straight section of the needle, leaning out the fuel mixture that should only be coming from the pilot jet at this stage.

BUT I think the main jet does cross over from very low throttle openings and the richer diameter needle may actually allow more crossover, as the thinner diameter probably isn't as effective at shutting off the needle jet nozzle at the low throttle openings.

Thoughts?

 

[@enrico@]

The 'J' diameter needle with its slightly shorter straight section would be on the taper slightly before the 'G' diameter needle is. In theory this means that the 'G' diameter needle should be leaner at part throttle openings then the 'J' diameter needle due to the slide being able to open more whilst still on the straight section of the needle, leaning out the fuel mixture that should only be coming from the pilot jet at this stage.



Thoughts?

Wrong.

The taper is fixed so increasing the diameter reduces the straight portion but at the same opening cone of the "J" will be leaner of the straight part of the "G".

Draw a straight line leaning to the right and then draws a horizontal line that crosses, this is the "G".
Now draw a parallel to the horizontal but higher, this is the "J".
As you can see the straight part of the "J" ends before but the diameter is greater until you reach the line "G".

Sorry for my english

 

[n_green]

Makes perfect sense to me actually. I see what you're saying in that the J needle will get leaner in SIZE then the G on the final part of its travel before hitting its own straight section, but my thoughts are since I would be using a much smaller pilot with the G compared to the J the actual air/fuel mixture itself would be leaner.

I could be wrong but does it make sense? Be good to have my own dyno haha.