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Carb Re-Jet Kits

Discussion in 'Bling and Appearance' started by craigrider, Nov 10, 2009.

  1. Probably less relevant here than in the US. US bikes (especially those for California) are generally jetted very lean in order to pass emissions regs. Australia, at least until recently, didn't/doesn't have any emissions regs for bikes beyond a prohibition on making smoke. Check pretty much any bike's manual and you're likely to find different jet sizes and needle specs for the US from other markets. Needles are often non-adjustable in US bikes too, so you can't play with clip position.

    I'm not saying there aren't Aust market bikes that wouldn't benefit. Maybe there are. But I'd want to be pretty sure the jetting in my bike wasn't optimal before I started stuffing around. Contrary to what such kits generally claim, messing with carbs generally requires a fair bit of fiddling about and testing, followed by more fiddling, followed by more testing to get spot on. My experience of bolt in kits in the UK is that they err towards the ridiculously rich as a default to avoid claims for melted engines. Fewer people demand compensation for using twice as much fuel as they should.
  2. Yeah I've heard more bad stories than good about american jet kits on Australian bikes.
  3. What bike do you have? I rejetted my 2008 GS500F myself, it needs 3 jets which are about $10 each, earlier models (pre-2001 IIRC) only need 2. Changing jet size also depends on you mods (if any). On a stock bike going up 1 step can be good, but if you have intake and exhaust mods you're go a lot bigger.

    With my intake + exhaust I went from 17.5/60/132.5 jets to 20/62.5/147.5 and it runs perfectly. But selling a kit for "one size fits all" won't get you the best result.
  4. Cheers for the replys guys thats some good info.. especially about the US emission requirements I would of never thought of that!

    I have a GSF250V Bandit (for a total of 5 days now) with a madaz exhaust so that would be the kit for my bike, they do ask you to specify your mods (intake/exhaust), year of build and altitude so they can send you the right kit for your bike.

  5. dont bother no need to to rejet with just a slip on.
  6. Instead of guessing why not put it on a dyno for AFR (Air Fuel Ratio) analysis. Looking around $80 max. You could also then provide the dyno results, current jet sizes, and other specific info with your order??
  7. Zbike - thats a generalisation. I'd have a play with the needle height at the very least, if not go up a jet size on the main(s) and see how it goes.

    Essentially you want to modify the bike then try replacing your main jet with a size larger until you get the strongest pull at high rpm (top third or less of your bikes rev range). From there you get ever more specific, modifying needle/float height, pilot jets and mixture screws until you get the exact characterstics you want. I'd follow this guide, it seems alright.

    General rule of thumb is that you'll go up one jet size on the main for a less restrictive exhaust, and then another one or two if you add a performance air filter - especially if pods replace the stock airbox.

    I'll use my Suzuki GS850 as an example, it came to me with a non-standard 4-into-1 exhaust and I then fitted individual pod filters to the carbies. I had to rejet up 3 sizes on the mainjet (from #115 to #130) to get it to rev to redline (9k), previously it'd top out at 4k because it was so lean. I may need to go up another size depending on what the onroad performance is like - its currently unregistered and I havent road tested it in current tune.

    At the end of the day its a bit of a stuff around, but its relatively simple and is quite worth the time you'll put into it.

    Cheers - boingk
  8. Yes, I agree that if the bike has been modified, jetting is likely to need alteration but mods weren't mentioned in the OP.

    Even so, it can make more sense to buy individual jets rather than a jet kit. I've been looking at a pipe and some airbox mods foir the DR and considered a dynojet kit, but when I looked into which bits I'd actually need, it turned out I'd have ended up using one main jet out of the whole kit. That makes a very expensive jet. Expensive enough to cover the cost of a whole bunch of OEM jets to allow me to get main, pilot and air bleed systems spot on, if I can be bothered, and still leave enough change for fish and chips.