i just installed a new fuel sending unit and tank.after installing it and putting gas in it my gas gage never moved.put 5 gallons in it.i figured not enough gas,drove to gas station put $20.00 in gage went to 1/4 tank,than went to another station filled up car.gage read full,but as i drove it a few miles burned off some gas,gage went to 3/4,than1/2,than1/4,than empty which is were it is now.i was told you have to set the unit to work properly,is this true.there were no instructions in box.if so how to do set the float for a 16 gallon 1972 dodge dart gas tank.any help would be appreciated.
thanks
butch

The factory gauges were never all that accurate; some tanks had odd shapes and the resistance is pretty much linear with the angle of the arm. Any calibration is at best fairly crude.

Basically, all you can play with is the length of the arm and the offset of the float. The resistor swings through something like 110degrees for factory, somewhat less for the aftermarkets I've used. Double check that your float is OK; I've seen a number spring big leaks loose buoyancy. Test the sender before you install it in the tank so you know that you get the full E-F range at the display as you swing the sender its full range. Then, with the tank empty and the sender installed, make sure it reads E with the tank right side up and F with the tank upside down - that tells you the float & arm aren't hitting anything; that doesn't tell you that it's adjusted right.

A factory-type replacement doesn't let you change the arm much; you can carefully bend it to raise and lower the display w.r.t. the level. Some aftermarket ones (like the one I got from J.C.Whitney) let you easily change the length of the arm as well as bend it. I've cobbled a factory and a JCW aftermarket one together when I just couldn't find a correct replacement; ugly, but it worked.

I would suggest you carefully (without stressing the delicate variable resistor) bend the float arm down (toward the fuel pickup) so the bottom of the float is roughly even or no more than 1" higher than the pickup; test that it says E on an empty tank, then put in 2 gal and see if it reads slightly higher than E, then 6 more gal and see that it's between 3/8 and 5/8, then fill it to see that it says F and that's probably the best you can do. Most people expect 1-2 gal left when the needle is on the E.

Good luck and be careful; we've had 2 local car guys killed by gasoline fires in the last 2 years.

thank you for everything,will try this on monday.
butch