specific gravity of fuel & jetting


this is for you ultra-techies i have a question that needs an answer, let's say if i was using a fuel of high specific gravity (.735) & switched to a fuel with a low specific gravity (.690) will i have to change my jetting to compensate for the low spec-grav fuel? which way? bigger perhaps?
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Tiba Karotsu:

Are you playing in the major leagues?..oterwise you don't need to deal with this....but anyways, you ask for it:

Yes, if you change the fuel for another with a different specific gravity you'll have to re-jet your carb.

The specific gravity is the ratio of the weight of a given volume of a fuel to the weight of an equal volume of distilled water, which is arbitrarily assigned the weight of 1 (One).
So, if you have an specific gravity of gasoline of .72, it would weigh approximately 72.

The ideal air/fuel ratio for spark ignition engines is generally quoted as being 14:1. Therefore, you need 14 pounds air for every pound of gasoline that enters the combustion process, through the carburetor or fuel injector system.

You need to know the weight of the fuel so you can adjust to the proper air/fuel ratio. Keep in mind that, normally, people tune to between 12:1 and 13:1 air/fuel ratio. You want to be more to the rich side as 14:1.

As you can see, you'll need to know the CFM's entering to your carb to adjust this.

Happy Tuning!!!


oh yeah you can say i'm playing in the big leagues :8, i have to take my scooter tuning seriously as i'm spending lots of my hard-earned money to buy the 'good stuff' the big fishes use & they have a lot of money to burn than i can earn in a lifetime.

thank you for your help you have enlightened me on this topic now i know which direction to take in my quest for higher hp & lower et's.

Gracias Senor Mexicano. :) till next time.

Tiba, I didn't realize that there was that kind of quality control with the fuel that was available in your part of the world? (i.e Jaso standards)

Tiba's a "heavy hitter". :)
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