i need advice - 250 exhaust and jetting

[angrypom]

i have just found out that the rta has screwed me again and i have been caught out by the new rules regarding p plates, so i am stuck on a 250 for 3 years. So i have decided to make a full better flowing exhaust system and shorty my can. what i want to know is, will i have to rejet my carbies to compensate for less back pressure or something like that.
Any advice would be really good.

[WATEVR]

it is best that whenever you modify exhaust or intake you get the bikes jetting to suit.

i wouldnt stress about the 250 issue, i know a couple of people that have made many guys on bigger bikes look silly on rs/ rgv's

if your a big fella or have to travel a fair distances for work etc i think you can apply to get a bigger capacity

[angrypom]

so would i see a profesional tuner or is it something i could go about doing myself? where would i get new jets from?

[latheboy]

"will i have to rejet my carbies to compensate for less back pressure or something like that."

Yes .... The easier the air gets out means more air going in ... If you dont change the jets it'll lean out and worst case go kaboom... It doesnt matter so much if its only a little bit lean, Its not a fully loaded wagon with a caravan on the back going up a big hill. Mines not perfect and i have a dyno.

Heaps of people have done it them selves before so you can do it, or get it on a dyno for the easier option.

[Gix11]

quote:Originally posted by angrypom

so would i see a profesional tuner or is it something i could go about doing myself? where would i get new jets from?


Most dyno guys would have the jets there to suit, if not just go to your local dealer, they're pretty standard items, but they ain't cheap! Don't go changing them williy nilly or else you'll open up a whole can of worms. Get the can on first and then take it to a dyno for an AFR reading. If he's good he'll advise you on what jet sizes you need to try next.

[ralph]

Stick some 250 badges on a busa

[angrypom]

very good ill start modifying

[angrypom]

i was just going to cut out my cat and shorty my factory can. i think that will be flowing enough.

[livewire]

Be aware that you may also have to step up the pilot jet as well. If it gets a flat spot midrange, it may be leaning out on the pilot jet. Sometimes surprising how far up the rev range before the main jet cuts in.
See if you can source some jet reamers. If you think you've overdone it on the drilling, I've also soldered up jets and redrilled them, previously. Not ideal, but saves running backward and forward to shop getting jets. If it concerns you that that seems a bit 'dodgy' you can measure em and put oem in when you're finished tuning.
Livewire
What about pod aircleaners, they liven things up a bit.
my experiance has been:
Exhaust up two jet sizes, mains, maybe none on pilots, but check for 'coughs'
Exhaust and pods, up 5 on mains, 3-4 on pilots

[livewire]

Just readin another post that reckons open pipes can fatten the bottom end. I haven't found that, but a good way to see if it is lean is to 'sneak' the choke on a bit and see if it improves things.
G