S3 Race 250 Port Matched Cylinder and Head

[lonetree]

That is the coolest little story out. love it, good thing you found the poor little fella.

[Jakobi]

Put some more time on the bike today to evaluate the jetting and get a feel for the 250. I'm really really enjoying the stability that the head mods have made. The engine now gives fanastic feedback and each change is more definite in how it reacts, but also less extreme.

At the end of the day N3CJ #3 is perfect power. Half a clip richer and you get the burbles. Half a clip leaner and the power flattens out a touch on the bottom half of the needle (off the pipe). Feels like it takes a little more to put it on the pipe too, and then the bike hits hard. Thats how I had my 300 set up but it required a full clip leaner to do it, and going back the other way the bike would burble with only a half a clip. Its much more stable now and made the process a real walk in the park. I hope the fuel economy still comes in around where it was. I'd like to be able to get around 100km from the tank.

[andoman]

I'm curious about the economy, too.
I would think that a 250 should get better economy than a 300. However, a 250 has to be pushed harder to go as fast. But if you are on the pipe more, the economy should be better since that's where a 2-stroke is most efficient. But if you average a gear lower on the 250, then your drive is less efficient...
Like I said, "curious."
Which reminds me: did you keep the same final gearing?

[GMP]

Jake,

That should be no problem with decent jetting especially with the head mod. All of my 250s would do that easy, with 13/52 gearing in mountainous terrain climbing or on the gas in sandy conditions.

[Jakobi]

I have no intention of changing the gearing for the riding I do. The bike will still lug down to second gear and pull tight single trail uphill switchbacks. I can chugg around at walking pace in second. Open the throttle and take off cleanly. I currently have 13-50 though so I am a bit shorter than stock.

The jetting definately feels and sounds a bit richer than I was running on the 300, which is what you would expect going a clip position richer. I had run both clips back to back on the 250 and there is a definite mid range boost in position 3. Half a clip leaner the bike runs super crisp and clean, but just doesn't seem to have the same punch off the bottom end. Its weaker and smoother on the bottom and much more pipe orientated. It turns into your typical 2T screamer. This is how I ran the 300 and the extra bottom end of the 300 compensated. The end result they both feel very similar.

The pros are that the 250 has much less noticable vibration and definately revs up quicker. The handing is much improved, but a lot of that could be attributed to the TTX forks.

As for fuel economy time will tell. I used to push the 300 every chance I got and always got pretty decent fuel range. Granted a tad leaner on the needle, the squish height was 0.8mm larger. I'll definately be setting the 300 up with a single base gasket next time around which will put me at 1.15mm squish with the high comp insert. I'll need to crunch some numbers to see how the CR will turn out and if I need Dave to take some out of the bowl for me.

[Jakobi]

Back to 42 N3EJ#2 178. The bike definately loses some bottom end torque going a half a clip leaner but it just feels so much crisper and reactive. Definately runs better for the type of riding I do.

In other news I was checking the bike over tonight as I'm taking it on an adventure to break in some new trail and noticed someone has done the sly on my ignition switch. It was sitting in rain mode. No idea how it got like this or how long its been like this, but I was wondering why it wasn't hitting as hard as I'd expected. Update tomorrow. Might take some video too.

[Jakobi]

Special package arrived from Dave earlier this week. 3 x PV spacers each 8mm thick. Anyone experimented with different PV volumes to determine where the sweet area is? From what I have read the spacers add torque to the bottom end, but also make it less snappy. I might start with 1 spacer and see if I can notice any difference. Has anyone noted any jetting changes required when adding volume too?

[Jakobi]

Also a little update from the previous post re jetting the 250. Have moved back to 45 N3CJ#3 178 until the N3CW arrives which I hope to be able to run with a 40 pilot in clip 3.

Custom sticker kit is on the way from ride PG which I may or may not install. I might save it until the old stickers are shagged out.

Ohlins TTX setup in the front is running well with the .46 springs, however after initial break in around 10hrs I plan to change the oil out and make any adjustments to oil level based on how they handle a decent ride. Will drop some fresh seals and bushings in at that time too. TTX shock is going in tomorrow morning with a 5.4 rate spring.

[Jakobi]

http://www.gasgasrider.org/forum/sho...9141#post89141

Update posted in ride&pics section.

[djroggen]

Originally Posted by Jakobi

It really blows that you need to drain the coolant and remove the water line housing to nip the front 2 bolts up!

You should not need to drain the whole system, if you just take the bolts out of the rad hose connection and pop it loose there is enough suction in the system to keep the antifreeze in.

My Star Head leaked with the bolts they gave me too, the bolts look sweet, but I had to replace them. I used the factory head bolts so I could actually tighten them, and added some antiseize while I was at it. They didn't have much room but once you get them tightened down they fit perfectly.