modifying Spark arrestor and proper jetting?

I will be uncorking my stock 07 xr650r in the next couple of weeks. The plan is to do the standard uncorking procedure, with one minor change. I will be boring 2" holes directly into the internal baffles built into the spark arrestor, as well as removing the tiny outlet. Has anyone modified their arrestor in this way? what effects will it have on my low end and jetting (if any at all)?

Also, Those that have uncorked, did you need to get Honda P/N: 16012-MBN-641 - NEEDLE SET, JET? Some sources I read on uncorking state only the low speed and main jets, then others state to get this extra part number as well as the low speed & main jets.

Here you go:

http://www.xr650r.us/jetting/

Abuser,

Look Bru, you've got the latest & greatest Pig one can have, the 2007 model, the newest one can get. I know, the same as all the other models, but that year's model is worth a bit more simply because it's the last made - and now you want to save two dollars on a needle Honda says you need but some forum dudes say you don't?
The decorking procedure/advice originates from Honda them selves. Sure, they were twits to cork it, but I trust their corrective advice. Did it too, also on a '07, and it transformed the bike beyond belief.
Mind though, your altitude plays a role in jetting, and Aurora's link should help you here (I cannot open it but think I know what this link contains, seen it before and used it).
No idea if you're the new owner of this bike or if you already had it for eons, however I'll tell you this: in corked form this is a sluggish shit bike, it won't even tickle a ballhair. But open it up, you might grab for a nappy
Enjoy!

As my good friend Burp suggests why skimp on a few $$$ do the job properly...check out ebay I just brought this tip for mine....$6 posted ?.
http://www.ebay.co.uk/itm/180838488718?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
That is the stock uncorked tip which I am sure is classed as the HRC tip maybe Burp or some of the other can confirm, I think there are only 2 tips.....
1. Stock Restricted
2. HRC / Unrestricted (Requires Rejetting)
Removed the 2 rubber airbox restrictors and that's it.

I did mine and fitted the following...along with the tip of course
16211-MBN-640 ~ CARB ISOLATOR ~ £14.50
99101-357-1750 #175 ~ MAIN JET ~ £10
16012-MBN-641 ~ MAIN NEEDLE ~ £26.50
99105-MBN-0680 ~ SLOW JET ~ £11

Please don't let my ignorance be confused with being cheap. I paid good money for this bike. I wanted the newest and cleanest stock bike I could find. When I found this beauty I coughed up a pretty penny. I only ask about the jets because I was unsure if that particular part was just a stock set? Seeing as it wasn't mentioned on a few 650r FAQ sites I was unsure. I could care less about the cost. Also, I picked up a billet tip, I did not want to modify my stock one. How does the hrc tip from Honda compare to the cheap screenshot billet tips, in regards to power and performance? Sound is not an issue, I only care about the best performing option. Also, what kind of gains would I see with a full blown after market header and pipe setup vs. The hrc tip stock setup?

There you go A, you sound heaps better. Best? Pro Circuit T4! This silencer has a sterling rep on this bike. Loud as fak but that tickles my fillings, call me kinky. I also have XRsOnly headers instead of the restricted std one's, but here quite some options are out there - including keeping the std's, some say that the very lowdown torque is best with them (I notice zero diff fwiw).
I bought a handful of jets to get the jetting spot on as I live on a highish altitude, but I quickly changed to a Mikuni TM40 (pumper carb) because of the more direct "urge" the engine has with it, it lifts on twist now, zero lag as with the std carb - which is good, make no mistake pls, I only think the TM40 is better. And easy to jet correct, I wager the remark here that it's the easiest of pumpers out there.
Yeah, you ask for converting the std silencer. Take it off and feel what it weighs... you'll be running to the shop I bet, and not for a hrc tip. Sure, word has it that works fine, but be honest now - you think it looks good? A T4 does, is lighter, obediently barks at you, and you can hang the std thing on your bar.
If you want something different than the run of the mill (me!) then find BigGun exhaust on the net, the full system. Their headers run INside of the frame, they look superb and they perform very well too. Bit dear but I would have bought them if I had to do same now (found them too late).
Mine's also a '7, bought it new, cost me a lot too - so I've bought decent stuff for it. Have not regretted an iota yet...

Well I must disagree with Burp to a certain amount I would consider how you ride before spending serious money on a system, I ride dead slow, bike is geared as such and stock system...I know it maybe heavy but my baby can handle the weight without to much trouble, this system fitted with the HRC tip and jetted is a great set-up, the billet tips I feel would loose you some low down torque, they are to open; people drill out the restricted tip to big they should only go out as big as the HRC diameter + they sound dreadful my bike came with 1 of these and I soon altered it down to about 38mm diameter. If your hell bent on speed and airflow then get your full system mod your airbox and rejet and enjoy

Abuser,

Mauser says he rides 'dead slow'.
If I tell you that his other bike is a Kwacker 1200, you believe him?

If so I'm Santa, live on the North Pole, Street 1, no.1
Need some ice, pls send some.

Exhaust:

http://www.xr650rforum.com/t953-which-exhaust?highlight=Exhaust

BuRP wrote:Abuser,

Mauser says he rides 'dead slow'.
If I tell you that his other bike is a Kwacker 1200, you believe him?

If so I'm Santa, live on the North Pole, Street 1, no.1
Need some ice, pls send some.

Hey I can guarantee my bike has not seen more than 55mph since I owned her, I ride her slow and enjoy watching the world go by at a slow pace . When I fire up the ZX12-R it's so hard to keep the speed down she just loves going fast.......
But I don't use it very often and prefer the slow pace of the BRP, maybe cause I'm getting old lol.

I would not say I will be riding "slow" but I definitely do not want to hurt low end torque, this power down low makes it easier for trail riding in rough wooded terrain and in the mountains. If the HRC tip is my best bet then so be it. Ive been hearing a lot about the Barnum exhaust, but have yet to see any for sale. my airbox will be uncorked with a UNI filter and side panel mod as well.

Put it this way I picked up a tip for £6 posted, you could do the same I am sure....try it, you have nothing to lose but if you don't try it then go spend hundreds on a system you will never know if it works or not.
Save the money fit the tip with the correct carb parts etc and ride her...if your happy send me £50 and spend the rest @ our website.... www.xr650r.co.uk added some nice second hand parts yesterday

ordering from the UK would be too costly. I am on the lookout for an ebay HRC tip. I will compare it to the billet tip I picked up for 20 bucks.