2014 Gas Gas 300 - Jetting

[n_green]

I copied the above info as information of what has gone on since my head was modified.

What happened is I got the head back and the new squish was 1.5mm, I rang the tuner and was told it should have been 1.3mm. The tuner was going away on holidays for a while so until he got back and after consulting with him about it we agreed a suitable option would be to replace the stock .5mm base gasket with a .3mm base gasket which would reduce the squish to 1.3mm. With the .3mm base gasket with new squish came in at 1.2 ish. I don't know what the new CR of the modified head is. The tuner reduced squish, re-cut the squish band angle to match the piston and modified the bowl. I was told he would raise compression a little as he isn't a fan of how low they are stock.

Now, obviously the ports have been lowered .2mm. Stock with a .5mm gasket the piston at BDC was a mm or 2 above the floor of the exhaust port, now it would be 5mm or so above the bottom of the exhaust port.

As far as I can tell this hasn't cost me any top end or mid end, in fact these are probably stronger since the mod.

But the bottom end has gone to hell, its still just as strong as pre head mod, however I can't for the life of me get the jetting dialled in. Pre head mod I was super happy with the jetting and fuel economy. It did have a burble at 1/8 throttle that I couldn't get out but that was about my only complaint.

Since the head mod the jetting has constantly been super rich off the bottom. I've tried a W and J diameters and even when they are perfect at idle and off idle as indicated by the air screw and feel, as soon as the throttle gets twisted it breaks up and burbles all the way through to just before 1/4. From there, as it was pre head mod it is beautiful.

One thing the head mod has done is allow me to drop down a size on the pilot, whereas I had to use a 42 and W dia needle, I can now get away with a 40p, alternately I can use a J dia with the 42 pilot.

There was less of a burble using the J dia 42 pilot but it was still rich, and no matter what combination I've used since the head mod it is consistently using more fuel then pre head-mod.

I'm almost considering buying an NECK and throwing that and a 45 pilot in.

So my question is this, has changing port timing somehow turned my bike into a thirsty hard to jet on the bottom mongrel? Because at this point in time I think it has.

Either way tomorrow I'm swapping the .3mm for a .5mm base gasket, and sending the head back to the tuner to be re-corrected. I'll also speak with him about this issue and see what his take on it is.

[Jakobi]

My 2013 model isn't as clean off the bottom as my 2010. It doesn't feel as strong and punchy either. But they are running different jetting setups. I wonder how this latest batch of cylinders looks casting wise?

[n_green]

My '14 looked just as clean as the '11 cylinder casting wise. Nice smooth ports. No idea about anything else, I didn't take measurements and it wouldn't have meant much to me if I did anyway.
What's confusing me is I can have it perfect at idle and off idle response but then it breaks up rich instantly.
Leaning it all out by raising the clip then leans out the mixture as it comes into the taper too much and it becomes snappy and loses some power.
Maybe I just need to custom grind my own needle.... Haha

[n_green]

Pulled the jug this morning, confirmed that using a .3mm base gasket I have 1.22-1.25mm squish. With no base gasket I have 1.02-1.05mm squish. With a .5mm I'll expect 1.45ish mm squish.
The head shows that on the carb side it is a nice mixture and the bowl was a light caramel/honey colour. At the front of the head/exhaust port side it was black and spoogey.
ImageUploadedByTapatalk1407051111.076116.jpg
ImageUploadedByTapatalk1407051122.776416.jpg

[n_green]

I didn't take any photos of the jug but it looks the same as the one off my '11. It's also stamped 's3' on the bottom. What changes were made to this 'new cylinder'?
If anyone's interested and tells me what to measure I can while it's off.

[Jakobi]

I have a 2010 300 jug here I can run some calipers over if you want to compare. Basically you'll be looking at the height of all the ports. Are the boost ports at the same height as the transfers, etc. Google port mapping.

I've noticed my 250 starting to feel a bit soft in the mid. Not soft, but just not as snappy. At around 55hrs now I think she's starting to show initial signs of wanting some rings/piston. They haven't been a soft 55hrs.

[n_green]

I'll have a google and if it looks easy enough ill measure it and put the numbers up. Maybe they'll make sense to someone, not me though

I measure my ring gap and after 25 hrs they are exactly the same as they were when brand new clearly I don't thrash it as much as I would like to believe.

[n_green]

http://www.macdizzy.com/cyl_primer.htm

Very interesting reading.
Well some may call it interesting.

[n_green]

I didn't bother taking measurements, looks like unless you are very accurate there is not point, plus the figures won't mean anything to me, and to be honest the Gasser is responsible for my pedantic jetting and suspension already, I don't want it to be the cause of some newfound passion for porting :roll eyes:

I did however take the jug with me today to my local dealer as the mechanic wanted to compare it to previous years, he had a brand new '13 cylinder there and to the naked eye they look identical.

[n_green]

Follow up, got the head back from being re-machined. By my verniers the squish with a .5mm base gasket was 1.42-1.45mm. The tuners verniers gave a reading of 1.35mm. 1mm was shaved off the gasket surface which should have given a squish of 1.25mm. By my verniers the new squish is 1.33mm. Close enough



Threw in the tuners recommended specs based on 14's he has run on the dyno - 40p, NECJ#3, 168m. I erred on the side of caution and left a 170 main in, down from the 172 I had been running previously and had been happy with.



Surprisingly the bike is happy running a 40p and J diameter needle, air screw is set at 1 turn out. Previously it would not have liked this and the air screw would have been at .5 or similar, so the closer squish has helped.



I only rode for 30k's at the test track I've found nearby (thanks to whoever it is cut that in), avg temp 14 deg C, altitude of 350m, humidity between 80-90%.



As per usual whilst the bike had a good idle (which got worse as the day went on thanks to the approaching rain storm and skyrocketing humidity) and then broke up burbly and rich immediately.



Today was a bit different too in that the top end wasn't as good as I remember, at the start of the ride when the humidity was lowest (though probably still at least 80%) it struggled to lift the front wheel under power, as the day went on and the rain came in it seemed to get better but still not as good as it has been. Not sure if I'm rich or lean, more testing will reveal the truth.



And as per usual economy was ordinary - 3.4l used for 30k's = 11l per 100km.



Not good enough


http://youtu.be/1gbScbv_1Ew