Is rejetting the carbs the equivalent of fine tuning the carbs for the same fuel and air mixture in each cylinder?

No ...
Cool.
Buddha.

To expand on Buddha's concise answer, rejetting is replacing the little screw in jets in the carb to allow more or less fuel flow.  Syncing the carbs sets them so they flow the same air and fuel relative to each other.

Thank you for the concise and the not so concise answers.

Is rejetting required with a stock bike with stock parts and stock adjustments?

Quote from: nemuro on July 14, 2009, 01:47:22 PM
Thank you for the concise and the not so concise answers.

Is rejetting required with a stock bike with stock parts and stock adjustments?

Any bike can be made better by rejetting.  The factory setup isn't that bad for a stock bike, though.  No real horsepower to be gained.  

You might just want to leave it the way it is till you add performance parts (and have to rejet).  

I believe every bike sold in USA with carburetors, for road use, in last 30 years is mandated by EPA to run lean.  Its emissions controls. Therefore they are jetted by factory run lean in USA. Most noticeable at low rpms in my humble opinion.

Re jetting to take away the lean run condition on an otherwise unmodified bike improves drivability especially at low rpms. In theory it should reduce MPG but you find you can use less throttle and lower rpms when not tryingto gofast, so MPG rises, at least mine does.

Synching has somewhat similar effect, the carbs are balanced after synchronized so its smoother and runs better at low rpms.

My ex250 pulls from 10 mph in top gear on level ground after jetting; before jetting it needed 3,000 rpm to not buck and shake.

Ummm synching is to equalize the bang from each cylinder making them the same at idle by adjusting throttle linkage between carbs - relative carb opening between carbs. Runs smoother. The equality of power output between cylinders is somewhat extended up the rev range, not perfectly due to tiny imperfections in linkage and other parts of the engine such as valve wear, compression, etc between cylinders. in fact one carb might even be open more than another when the cylinders bang equally at idle. But idle is where everybody synches them, its easiest.

it says he's in romania.  Every country but the US gets the right size pilot from the factory (if I remember right).  The one we swap in to get rid of the crazy lean bottom end is the one they already have.  But I totally agree with you that cleaning up the bottom end with some jetting is something even a stock bike can benefit from.

+1 on the sync too.  I don't know why more people don't do it on a regular basis.  

Cool to hear you have an ex250.  I used to have one too.  It was the funnest track day bike ever made, and surprisingly capable.  I kind of miss it.  Do any mods yet?

Oh, and welcome to GStwins!

Thanks for welcome.

The 1988 ex250 has been in my shop for ten years now. Some years it was my big bike (SRX250). Has roller headset, racetech emulators and non-progressive springs, ex500 OEM shock/spring. Stage 1 jetting - dynojet. The headset was slightly noticeable, the rest very much so. I also gooped every connector on the bike with dielectric grease (that multiweight vaseline in a tube for other readers) so it runs fine in the rain.  Rear light mod so taillight has directionals, it was sold in US with empty bulb holes in rear reflector on each side.  Mild stuff, these mods. 

I have not figured out how to mouse proof the garage. Blew out oaknut dust from carbs 2 weeks ago.  Made plugs for airbox holes and mufflers from hardware store rubber stoppers with screws for handles but got lazy. 

The 1988 ex250 sits patiently awaiting new carb-to-airbox boots ordered locally. its 21+ years now and they are hard and deformed and won't go on right. Boiling helps but they cool to a weird shape and pull themselves off the carbs.

This weekend I will have both airbox boots and new old GSF and rare warm dry summer NH weather. Think the EX will sit a while. Will ride GSF from Gorham NH - GSF selling dealer - on rt 2 east into Rumford Maine and beyond and back southeast down through western Maine to Conway area.  Not exactly Deals Gap but nice with light to zero traffic. 

Funny thing is last year I bought a clean 1999 miata to serve as all weather motorcycle, and it does, but it didn't change that I want this next motorcycle anyway.

sorry to threadjack.  

Cool, mine was a 92 so they're identical if I remember right.  Same 14,000 rpm redline and 15,500 rpm ignition cutoff.    I wish my gs could do that.  I got a little carried away with mine. Woodcraft rearsets and clipons, Works shock, Racetech emulators and springs, full muzzy, pods, dynojet 3, and on and on.  It was a totally different bike and it was worth every penny. Couldn't bear to part with it, so I sold it to my brother for pretty much nothing.  

Your trip thru Maine sounds cool.  Have fun this weekend.

Sounds like you have your hands full with projects, but in a good way.  When you get done with them you'll have to post some photos in odds and ends.