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I recently dropped my suzuki gixxer 155 for a servicing to a new garage. I noticed that the mileage that my bike gave was almost halved, from 37kmpl to 20kmpl.

Took the bike back to the garage. The guy changed the now old spark plug, which he said 'may' lead to some drop in mileage. And, he noticed that the choke was on. So, he said that the dropped mileage was because of the choke.

I am kind of skeptical how that kind of a drop in mileage happens with just the choke being turned on. Hence asking, is that really possible or the servicing guy messed up something in my bike?

Additional context: Not sure if this'd help. There was an issue with setting the idle also after the servicing, before taking the bike back to the garage. It'd be too high causing the engine to revv too much in neutral or even in gear it'd speed up without me using the accelerator. Else, it'd get set too low such that the engine would shut down if i dropped the accelerator(even while driving). Finally found the perfect spot before taking it back, but the engine would still turn off once after starting. Issue was resolved after taking it back to the garage. But the mileage doesnt seem like its gone back up.

Thanks.

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It's entirely possible that the application of choke would contribute to reduced fuel economy. In an engine that uses a carburetor, with no choke applied, the airflow past the fuel jet(s) provides for an optimum fuel-air mixture.

For cold starts, one would like to have an enriched fuel portion. For the newer engines, the computer accounts for air temperature, engine temperature, etc., but on older ones, it's the nut behind the wheel that makes those decisions.

When the choke is applied, it closes off some of the usual intake cross-sectional area, which is "compensated" by air pressure from the float bowl, which increases the fuel flow through the jet.

Effectively, a partial vacuum is created when the engine is turned over and if air is not provided by an open throat of the carb, it has to come through (partially) from the ambient air in the float bowl, pushing more fuel.

A YouTube video pretty much covers it in the first minute.

This does not address the continued poor performance, but does answer the primary question.

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  • I would fully agree with you with a minor point adjustment ... in a normally aspirated engine, there is always a vacuum present. Just when the choke is applied, it creates more of a vacuum, and the carb behaves as stated. Apr 13 at 16:56
  • "A partial vacuum is created when the engine is turned over..." There would not always be a vacuum if the engine is sitting idle. I'm not sure where I made the error in phrasing.
    – fred_dot_u
    Apr 13 at 19:04
  • The greatest amount of vacuum an engine sees is with the throttle blades closed ... which is what happens at idle. All normally aspirated ICEs see vacuum while running, even at WOT. If there were no vacuum present, the engine wouldn't run. Remember, the ICE is, for all intents and purposes, just an air mover. I see I made a mistake in my first comment ... there will only be vacuum when the vehicle is running ... not much going on if the engine is off :o) Apr 13 at 20:49

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