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basically, i am not know much about bikes engine. i got a question when i riding bikes in downhill with lower gear the engine sounds very noisy I think engine runs more than the ideal speed, my question is it consume more fuel as it inlet and outlet valve opens very quickly, if there no supply of fuel why does engine sounds or how does engine runs more than ideal

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  • Welcome to the site Raj. Can a ask, by low gear, do you mean 1st or 2nd or low as in geared low, i.e. 4th or 5th?
    – Steve Matthews
    Commented Oct 29, 2018 at 11:49
  • Are you talking about using a low gear (as in 1st or 2nd) to descend a steep hill using engine braking?
    – charmer
    Commented Oct 29, 2018 at 13:01

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Riding in gear with the throttle off is the moment you'll burn the less gas ever. It's less consuming than staying in neutral and letting the bike going by itself.

The loud noise is just the engine being revved by the rear wheel and that is perfectly fine. You can downshift if you need more engine brake, getting lower speed and ultimately lower rpm if engine brake slowed you enough.

EDIT to support the fuel theory : https://www.popularmechanics.com/cars/hybrid-electric/a5977/coasting-in-neutral-fuel-economy/

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  • Only true for fuel injected engines - for Carburetted engines they'll always use fuel on over-run, dependent on the idle fuel usage on tickover and the actual RPM of the engine. i.e. using the 1 gallon/hour (1gph) idle at 1000 revs then pushing 4000 revs on a closed throttle with a carburretted engine will use 4gph.
    – charmer
    Commented Oct 29, 2018 at 15:21
  • Is that so ? I thought that having the throttle closed would only "use" the idle jet consumption. But thinking about it, that makes sense because the vaccum would still be more present than going at 1000rpm.
    – Pierre P.
    Commented Nov 5, 2018 at 16:21
  • Yes @Aziris The idle jet consumption is where most of the fuel would come from and a very small amount depending on needle valve/slide/butterfly opening. Compared to a fuel injected engine which can shut off the injectors fully while the engine is exceeding the set idle speed with no throttle.
    – charmer
    Commented Nov 5, 2018 at 16:34

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