I have a 1999 EVO Softail. Should the fuel in the right-hand fuel tank be 3/4 full while the left-hand tank is nearly empty or is there a blockage somewhere? Can anyone tell me what the problem is? Thanks.

 

There's a crossover hose connecting the tanks, the tank liner might be coming loose and blocking the crossover hole.

 

That or the vent in the right cap is plugged.
If you remove both caps and shine a flashlight in you can see the gas transferring between the tanks
at the crossover tubes

 

A liquid will always seek it's own level. If upright, both tanks should be at an equal level. If on the jiffy stand the left should have a higher level in relation to the amount of space it takes up than the right but should have about the same amount of fuel in it.
Something is stopping the transfer.
I agree with starting at the cross over.

 

What I have found in the past is that the older real rubber fuel lines get eaten up by Ethanal fuels. It will literally create a gummed up rubber plug in the transfer line between the tanks.. Ask me how I know... Replace all the fuel lines with todays newer EFI fuel line made to withstand Ethanol fuels...