what amp are you using and how is it set? is it bone clean or breaking up?
it could also be that your signal chain needs a nice strong buffer somewhere in it or the buffer you have is maybe misplaced.... how many pedals are you running and are they all true bypass?
what precisely is the effect order you find works from guitar jack to amp jack.... and what are the orders that are you suspect cause the fulltone to sound weak?
without hearing the tone you refer to as 'weak' (or getting a much better decription of how you are trying to use it) its hard to know if its something to do with the fulltone's interaction with your other gear or if you are looking for it to produce tones its not designed to produce... get ready for one of my grizzled old road warrior gear dissertations (skip this if you have a short attention span, read if you like a lot of techinfo as well as practical advice for working musicians):
see, I think the supa trem is a sine wave trem (I might be wrong) which is a softer and subtler sound than you may want, but its very much the vintage fender LDR trem style which is a soft pulse that's fairly subtle at a lot of settings...I can't remember if fulltone copied the fender circuit with solid state components or if he based his trem on the Electronics Australia project, but both are subtle sine wave affairs, though different sounding and are the absis for MANY trem pedals. if you want a choppy supro or vox trem get a pedal with more of a square shape and a really wide range between the high and low point of trem's volume range... catalinbread's semaphore and valcoder do a great job...
also, Mike Fuller's about my least favorite person in the world of guitar... maybe you should take it back to the store (or try to return it to the original owner if bought used) and buy a boutique trem made by a nicer group of people than Mike and his crew. Which would basically describe every other small company.... people who want fender 2x6L6 blackface amp type trem in a pedal tend to go for the Demeter tremualtor over the fulltone. A lot of people swear by the classic boss trem (TR2, right?) which is a no-brainer for build quality and reliably strong sound... and a surprising number of people favor the simple, plastic danelectro pedal neither of which are amp-like, but are great AND versatile. I used it on a track on record over the trem built into the 2 blackface showmans I ahd at my disposal. It just sounded better than the trem channel on the old Fenders, dunno why.
Personally I stick with all tube amp trem most of the time. For choppy I like the AC30 vib/trem channel set to max chop or for a subtler square wave Supros like the dual tone have a heckuva trem sound. But my favorite trem sound is Fender's small amplifier bias-vary rem that is a power-amp based effect first introduced in the famed tweed tremolux and carried over into the brown, black and silver princetons (and also the brown deluxes, but they are rare as hen's teeth anymore). It kills.
resume reading here
if something is giving you grief in your rig, stop fucking with it and return it or sell it and buy something that sounds good to your ear in the store that also has a long-standing reputation for reliability... the most expensive thing is not always the best thing. Only you know your sound, match the tools to the job and keep your eyes off the price tags and marketing hyperbole.
