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!!!