Hi all,

I have an 07 S40 with about 4000 miles now. Completely stock. I know rejetting carb & replacing exhaust, and similar mods can improve bike performance, but I'm fairly happy with the way the bike runs already. Are there any other disadvantages to simply leaving it stock? (shorter engine lifespan, etc.?)

Thanks!

Disadvantages.... hmmmmm

The Lean condition that Suzuki has the bike adjusted to meet the EPA standards for "off the factory floor" requirements will cause the engine to run warmer.   You most likely will get a discoloration of the exhaust pipe so it will not look as nice.

 You will also have to be more vigilant on monitoring your oil because it helps dissipate the heat and will have a slightly shorter life with the heat.  

Some will argue the a properly tuned carb will be more efficient thus giving even better fuel economy.   Counter argument is "What is properly tuned?"....  

I've been told that the EPA "Lean" is good for "off the factory floor", but it will cause other types of pollutants due to the heat reacting with the other chemicals in the fuel which isn't part if the EPA tests.  Also, I've been told that it will cause to bike to change in a few years of riding to be more polluting (not sure why...maybe the heat causing parts to wear faster ???).  

I'm not a metallurgist nor an engineer but in my mind increased heat translates to reduced engine lifespan - especially in hotter climates.

Yep those high temps are murder on your exhaust valves and exhaust valve seats. Ideally the exhaust temp should be in the 1200 degree range, stock they look like they run in the 1500 to 1600 degree range. Mine header(down)pipe still looks like new with 6500 miles on. Did carb mods right after I got it.

leave it stock and you could end up like my savage.
19,000 miles and one exhaust valve stem failed and snapped in half.
Most definitely due to running too lean / so too hot, (aggravated by an aftermarket exhaust that was fitted before I bought the bike).

My replacement engine will have new exhaust valves fitted and run a 155 main jet, plus the idle screw is coming out a turn or two.  

how would one acquire necessary parts to rejet stock carb on his own...   new screws, because i know they are going to gum up on me... larger main and possibly larger idle

Jomiyo
if you go to http://www.alpha-sports.com/suzuki_parts.htm

you can get all the parts for LS650 Savage.
I live in the UK and even though they are in USA I have bought quite a few parts from them myself.

If you want the bigger jets, as in 1986 to 88 model just browse to 1988 lS650 and it has the jets (and all other carb parts listed), later models list the 130 and 145 main jets.

I think the later models had a different slide, needle jet and needle as well as the main jet?
But if you just fit a bigger main jet and pilot jet then you will get a cooler running engine with a better idle and better mid range.