Units in stoichiometry $$C_x H_y O_z$$ 

1.What are the units of x,y,z.I've read that they're termed as 'stoichiometric coefficients'.

2.What is the unit of mass proportion of carbon(c) in the fuel?

$$c=\frac{M_{carbon}}{M_{fuel}} .x$$
The stoichiometric coefficients is something else than you suggest.
stoichiometric coefficients:
The number of molecules of a given component that participate in the reaction as written.
The indexes $x, y, z$ represent quantities of atoms in a compound. So they do not have any units.
@Q2 Do you know what are $c, M$ and $x$ in the equation? If you do, you can answer your question. If you do not, than you should find it out.