Changing Carburetor

Question

I am using Vespa P 150 x.It has a is 150 cc engine. The fuel average is not too much good.Some one told me that for batter fuel millage there is a option that I may change my original Vespa carburetor with the 70 cc motorcycle carburetor.The average mileage of that 70 cc motorcycle is 50 km per liter.

Technically if i change my Vespa 150 cc carburetor with 70 cc carburetor it will affect my ring piston/engine ? If no , what other aspects should i also see to change while using a 70 cc carburetor in P 150 x Vespa.

Need your kind technical opinion about it.

Answer 1

I cannot speak specifically to your model, but I will address how changing the carb will affect your engine.

You are wasting your time trying to haphazardly swap out some other carb. You need to concern yourself with jet size. Carb jet size will control the amount of fuel getting to your engine. Stepping up to a leaner (less fuel) jet size may improve your fuel usage, but it also makes your engine run hotter. On top of that, you will need to pay someone with a dyno to retune your needle settings to the new jets. This cost will far outweigh any fuel efficieny improvement.

The best thing to do would be to clean your carbs and/or replace the jets with new jets of the same size. A dirty carb will absolutely lower your fuel efficiency. Plus, if you choose this route, your Vespa will still run- unlike so many other vehicles who have had carb mods attempted.

Answer 2

If your carb is a Dell'orto SI type, it's made to run efficiently without too much hassle, and with the benefit of autolube. There are kits to install reed-valves and motorcycle carbs (typically Keihin PWK, Dell'orto PHBH, Mikuni TM series), but they're generally oversized to boost power, not to decrease consumption. In any case, if you feel you've been guzzling gas lately, it's more likely due to bad jetting, failing seals, worn piston rings, or a failing spark plug. Vespa P-series are reliable and quite sober from the factory, and as Justin said, just swapping to a different carb because the vehicle it's on seems to burn less gas is pretty much like installing the cord from the bedside lamp on the iron or the washing machine in hopes that they'll now draw less electricity...