Our fuel guage has never worked properly, despite having taken the float out and fiddled with it, then sealed with gas resistent gasket cement and resealed the opening cover. I had the panel off to replace light bulbs and found that the center nut was very loose on the fuel guage -- Yay! Must have been the problem! Nope. Still only working between 1/4 tank and 3/4 tank. So I took the float out again. Turns out that there is only a lmited area pointing to about three quarters forward towards the bow that is clear of fittings inside the tank and the screw to hold the float flat on the surface of the diesel was both binding backwards against the plastic fitting and was not level AND was likely hitting one of the fittings inside. I carefully reinserted, feeling for obstructions, resealed and BINGO! No further issues.
'91 C-36 Tall Rig, Fin Keel, Hull #1120, Universal M-35 original (not "A" or "B")
CBYC, Scarborough, Ontario, Canada