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fuel injection

Discussion in 'General Motorcycling Discussion' started by Raie, Sep 28, 2010.

  1. hi all,

    i have a question in regards to what fuel injection is and what benefit it has over whatever a non fuel injected bike is... i am a total nub to motorbikes so please excuse my lack of technical terms and jargon...

    i have been looking at the vtr250 and was originally tossing up getting a 2009 model as they are upgraded to fuel injection (and look nicer) however i cannot find (via google searching) what it was before becoming fuel injected - someone please tell me. and also what benefit a fuel injected bike has over it's predecessor.. my friend told me that you may damage your engine if you drop a non fuel injected bike for some reason... a bit too technical for me to remember. the word carby comes to mind..

    thanks in advance... apologies for my newbie questions.
  2. Carby, short for carburettor, and fuel injection both do the same thing on an internal combustion engine - they mix the fuel and air and put it into the cylinder.The obvious difference is that a carby is the old outdated mechanical method whereas fuel injection is modern and often electronic with the real difference being that injection is generally more efficient. Very simplistic definition there but I'm hoping you'll get the gist.
    As for dropping each of them I think you'll find that there's just as much chance of hurting something regardless of the injection method and I'm sure to be corrected just as much chance of you losing some fuel if you leave it on it's side for too long.
  3. Short answer. Before fuel injection was invented the piston sucked the fuel into the cylinder with the air. This process was undertaken by the carburettor and very precise valves to get the ratio of air / fuel "just right".

    Fuel injection however is exactly what it says, the fuel is injected at (supposedly) the exact quantity required for the amount of air "inhaled".

    However, technology has come a fair way now and new carburettors are almost as efficient as fuel injection (the difference in a well tuned engine is negligible).

    The advantage of fuel injection though, is that as the engine revs up, the "computer" that is handling the fuel injection can adapt instantaneously to the amount of fuel required, but a "carby" cannot. So the carby is made to perform a certain way and thats it, it can't adapt on the fly.
  4. Don't forget that a fuel injected bike means no choke, and it starts on cold days :rofl:
  5. TBH I think this is the biggest selling point of EFI.
  6. Hey! My carby bike starts every day, even 4am in winter when it has been freezing.....
    But then i had it serviced and balanced just before winter too :p Mighta helped.

    That said, hopefully the next bike has EFI, for the reasons above (ie: adjusts on the fly).
  7. thanks all. i guess i will stick to an older carby model then and think about efi for my second bike..
  8. Realistically, on any modern bike, it should be pretty much impossible to for the rider to tell whether it's carbied or efi'd apart from a need to use the choke for starting the carbied model. The real advantages of efi show up in reduced tailpipe emissions and imroved fuel consumption, with a side benefit that (some at least) are more easily adjusted to match aftermarket exhaust systems or hotted up engines.

    Carbs vs efi wouldn't be high on my decision making list unless two bikes were otherwise identically attractive to me. Then I'd incline towards efi, although 20 years ago, I'd have favoured carbs. That's a reflection both on the development of efi systems and of my own education and experience :D.
  9. Carburetors are just a fancy term for "controlled leak".
  10. #10 blackjacket, Sep 29, 2010
    Last edited by a moderator: Jul 13, 2015
    Carbies also produce backfires on the overrun because they have some lag time before cutting off fuel. You can [URL="]trigger[/URL] your own backfire by switching off the kill switch, then back on again while riding (at the peril of your exhaust). Or you can hit the rev-limiter on an EFI bike :-w

    But some bikes and cars just don't sound as good with EFI...
  11. My bike has a Carbie. Not having to use the choke and wait for the engine to warm up as long in the morning would be great. Also, backfiring, the loud "BANG" when you start your bike occasionally can be a pain during the early morning when you don't really want to wake people, or when your in an undercover carpark as the nosie and echo really scares the shit outta people.

    I'd definetely go EFI if I had a choice out of the two. Sucks that the EU Ninja's have EFI but AU/US don't :(
  12. As i stated, my ZZR250 (not too far different from your EX250J Locky (mines an EX250H)) fires right up. I max the choke, hit the go button, maybe 1sec of starter and she comes to life, wind the choke back as the revs climb to settle between 2500 - 3000 revs. Put my helmet on (15-20sec?), couple light revs to make sure the bike is picking up ok, sometimes needs 10sec more to rev smoothly... and once it does, go...
    I be a little cautious on the first intersection naturally, as you would on an EFI bike too - engine is cold! Being gentle, allowing the engine to warm some and the oil pressure to pick up, about two minutes of cruising along at 60 (for me conveniently the next intersection on my work commute) i kill the choke and shes good.

    edit: You need to get your carby serviced if you are backfiring on start up, and really having to wait for it to warm up - especially in QLD! :p. (maybe valves checked too?) Wouldnt blame the choke itself for what you are describing.
  13. Agree. I have a charby and it always starts with a bit of throttle, no choke, engine runs smoothly from the get go although I am always gentle for the first few minutes. Although I do live in darwin, occasionally we get a sub 20 degree C night.
  14. I have heard at low revs a fuel injected vehicle will run better as low air speeds in a carby don't always cause optimum fuel mixing..
  15. You all missed it;

    Carby bike; heaps of backyard mechanics can fix it if it goes shitfaced.

    EFI bike; people look at it, poke the wires and say it's stuffed and to take it to a mechanic. He then does the same thing replaces the injectors and hopes for the best...
  16. Yep - home mechanics tend do a full carby rebuild in a few hours. They need to be dismantled and cleaned occasionally as well, especialy if the bike is left with fuel in the carbies for a month or longer.

    Fuel injection is more reliable, more fuel efficient and will usualy last longer with less maintance. But if it goes wrong it's a job for the shop, and expansive.

    Depends on the type of engine and how the engine is tuned. A wrongly jetted or tuned carb will be a b!tch though (note to self - adjust idle air screws tomorrow)
  17. Theoretically true, but most modern carb setups are so good you won't notice.

    To a large extent this is an attitudinal thing, though. Aside from malfunctions in the actual "brain" (which aren't common) an EFI system is no harder to troubleshoot than carbs. Probably easier. Hell, the gear is now available for the amateur to build their own EFI system and, frankly, looking at what's involved, it's not significantly more challenging than sticking on a non-standard set of carbs (which can be very bloody challenging indeed, whatever the blurb says about a simple bolt on fitment :rofl:).

    But the great thing is that EFI simply does not go wrong. Well, it does, but automotive experience over tha last couple of decades suggests that it's so rare as to not be a major consideration.

    I've seen an awful lot of carbs comprehensively stuffed rather than fixed by backyard mechanics, so they can't be that easy :LOL:.
  18. Oi mine always starts :p She needs the choke, but by the time I press go, stick my helmet and gloves on she's ready to roll.

    It's no biggie. I've always been warey of this new fangled technology, every newer car I've owned has given me more grief than my first basic shit box that had a carby and my bike has never skipped a beat because there's very little that can go wrong.

    But it's totally irrational as, as has been pointed out, EFI is really reliable and any monkey can fix it. I'm just praying that my carby never packs it in 8-[