Carburators vs injection.

Discussion in 'Technical Help' started by Lucazade, Jan 25, 2013.

  1. So after pointless banter with a mate at work (he in to cars not bikes but still petrol in veins) a question came up. We were discussing a 1098, well engine not bike.

    At one stage he suggested that it would be cool engine to add higher compression pistons and convert it to carburator setup from injection. Conversion it self not a major issue of how to so no need to explain.

    However we both had no idea if it would be better or worse or maybe just different and why?

    Skipping the explanation that carburator setup is old school technology what would be the differences between the two?
     
  2. Nope, injection is superior to carbs in every way. When people retrofit carbs to an injected vehicle its for one of three reasons.

    1) the existing injection system is an early crude system

    2) tuning a bespoke injection system is beyond the capability of the person building the engine

    3) building and tuning a state of the art injection system is beyond the budget for the engine build.

    The basic function of any fuel system is to deliver fuel and air in the correct ratio at any point in time. There is no possible way a mechanical system (which has fuel and air governed by fixed jets and needles) can do this more efficiently than an electronic system capable of varying its fuel / air ratio in hundredths of a second, and responding to the engines sensor inputs.

    If carbs were better moto GP bikes and f1 cars would have them.
     
    #2 philoldsmobile, Jan 25, 2013
    Last edited: Jan 25, 2013
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  3. Agreed, and on engines with large cylinders (such as a 1098) carbs are very much a compromise, particularly on high revving engines as to get big power at high RPM requires a large carb but large carbs don't work well at low RPM due to low air speed/poor fuel/air mix so it's difficult to get the bike running well both at low and high RPM.

    I would say that fuel injection was a major contributory factor to Ducati's success in early WSB days, I doubt a carb'd 916/996 would have been anywhere near as competitive.

    That said I'm using big carbs on my Monster project...
     
  4. Yup, it all comes down to the fact injection is pretty much infinitely variable, and carbs arent, as they are constrained by fixed jet sizes. They are easier to make 'work' but you will never get them perfect. Carbs are perfectly capable of running very sweetly, but properly set up injection will be either more more powerful or more economical, depending on how its set up (or both if the carbs are worn or wrong)
     
  5. Carbs vs injection

    Fuel injection has been around for sometime and it's only recently that some of the basic problems have been overcome, mainly that injection doesn't efficiently atomise the charge and this leads to the cylinder walls being made wet with fuel. Multi-point injection has dealt with this but we are talking about the latest control methods. If you want this set-up on your machine either buy a new bike or expect a 4 figure sum. The early attempts at fuel injection must be very dated by now.
    Carburation distributes fuel by a slightly different method that being vacuum demand and inadequate atomising is not a feature. What is a problem is change of oxygen density - a cold day means more oxygen and a hot one less so. An engine jetted on a cold day can be significantly rich on a hot one. A way around this is to have a jet sequence vs air temp... or a fuel pressure regulator. Varying the fuel pressure changes the float height and the mixture ratio in turn. At 15C I will allow the carb 3.5psi, at 20C - 3.0psi and at 25C - 2.5psi. Of course it helps that the Weber has a fuel pump therefore varied fuel tank load doesn't figure in the equation, but a basic gravity fed, unregulated carb set-up is usually all over the shop. Which is why the average Joe spouts that injection is a million times better than a carb set up ever could be. It isn't and for obvious reasons that can be defeated.
     
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