xc300 parts combo?

[adv rider]

Well i'm about 99% sure I will be owning a newer{ 12/13} 300 soon. My question is: how are they for revving out? I like to put my bike in 1 gear and leave it there, so 2nd most of time and a little bit of 3rd.

Is there a good combination of parts to make it more mid/top power? head mod/pipe/porting{ by who?}/ etc. . Or will I find out, that's how a stock 300 is? Do I need a flywheel weight? Rekluse? Or do I switch over to a rb modded head on a 250 cylinder kit?
I have to set this bike up right from the start, since I plan to ride a lot more offroad this year. Sell my Harley, and concentrate on riding offroad



I may be a bit early to be asking about this stuff, but I like to work out my plan's in advance

Thank you

 

[bowhunter007]

and concentrate on riding offroad: transition, or giant

Those have pedals...don't they? My favorite gear combo is 2/4

 

[pscook]

Jetting and silencer will help the bike rev out. I have a 2011 300, and the Q-Stealth (stock) pipe didn't help the upper revs. I installed a Leo Vince silencer and the top end opened right up and allowed me to carry an extra 500-1000 RPM on the trails with existing jetting, thereby eliminating having to short shift. I am now getting ready to install a Lectron carb, but I am certain that the Keihin can be jetted to bring the top end alive.

Regarding having the head shaved, that is a good place to start as proper squish will help provide consistent jetting results.

 

[forgiven]

I think the key to carrying a gear longer is to stick with the 48 rear sprocket. In order to pull that off you may consider a flywheel weight, power valve chamber, and either Jacobi jetted specs or a smart carb. Haven't done the head mood but that would be advisable as well.I do almost everything in second. I will hit third at times in the woods but I am moving pretty fast at that point.

 

[adv rider]

300xc revving

Thanks for the ideas. A silencer change, FW weight, and head mod seems like a good start, possibly. But if I did go down to 250, will that affect the head mod?

 

[forgiven]

If you like to do the 2nd/3rd thing...stick wtih the 300

 

[gasser]

I had an 07ec250 gasser completely stock that would rev out great until I rebuilt it with a 300 top end. The bottom end was stronger but it killed the over rev and just wasn't nearly as much fun to ride until I sent the carb and head to RB designs. Ron Black worked his magic and the over rev was back along with more bottom. I do believe his work on the carb was mainly responsible for the added top end. With 13/49 gearing that bike would run 80-85mpr and cruise easily at 50-55. I will add that the bike did have the 2k3 ignition (bigger, heavier coil)

 

[wa_ndro]

Jetting and silencer will help the bike rev out. I have a 2011 300, and the Q-Stealth (stock) pipe didn't help the upper revs. I installed a Leo Vince silencer and the top end opened right up and allowed me to carry an extra 500-1000 RPM on the trails with existing jetting, thereby eliminating having to short shift. I am now getting ready to install a Lectron carb, but I am certain that the Keihin can be jetted to bring the top end alive.

Regarding having the head shaved, that is a good place to start as proper squish will help provide consistent jetting results.

Agree with this.
STEP 1 : remove Q Stealth and bike will rev

 

[Jakobi]

If you go to a 250 you'll need a 250 head to match the cylinder. I personally prefer the 250 over the 300. They'll both rev if you set them up to, and its more a function of port timing and compression ratio (determined when setting the head up), than the actual engine itself.

The issue for me was that a reasonably well (read not perfect) 300 had too much in the low to mid for me to push it aggressively without wearing myself out. If you like to hold a gear the 300 will be great. The 250 seems to work better the harder you push it, which includes clicking through the gears.

First stop set the ports using base gaskets for top end, then have the head machined back to where it needs to be volume and squish wise. Jet to suit and hold on tight.

 

[adv rider]

300 engine performance

If you go to a 250 you'll need a 250 head to match the cylinder. I personally prefer the 250 over the 300. They'll both rev if you set them up to, and its more a function of port timing and compression ratio (determined when setting the head up), than the actual engine itself.

If I had a S3 head,couldn't i swap between 250 and 300 inserts? Or Is there better performance from an RB head mod over S3 with changeable inserts?

 

[Jakobi]

Well yes inded if you had the S3 head you could simply swap inserts. However, if you wanted optimal fuelling doing it this way you'd have custom inserts machined up for both sizes too.

On my 300 with the ports timed for top end, and the highest compression insert (read tightest squish), the clearance still measured in at 1.9mm down from 2.6mm stock. You want to get around 1-1.2mm and that wouldn't have been achievable without either having a complete custom insert machined or milling the mating surface of the outer head as well as the insert which would make all the other inserts useless unless also machined to match the new machined head.

In the end I compromised on the 250 and set the port timing for more mid range which gave me the 1.2-1.3mm squish I was after. It worked out ok being a race ported cylinder that favoured top end anyway. On a 300 if you start dropping it too far you'll lose out up top.