Why does fuel light flash on 70ltres. when boat has 120 ltre.fuel tank

Hello!
"Buy a case of beer. Trailer the boat to the lake. Launch boat. Ride around the lake and drink beer and offer pretty girls boat rides until the gas tank is empty. SORRY - I just had to say that."

You can find the answer here:
https://forums.iboats.com/forum/general-boating-outdoors-activities/boat-topics-and-questions-not-engine-topics/471660-drain-gas-tank-what-is-the-best-way
or here:
https://goneoutdoors.com/drain-boat-fuel-tank-6156615.html

https://www.greatlakesscuttlebutt.com/news/featured-news/diy-fuel-tank-draining/

https://www.google.com/search?q=1975+bass+boat+ranger+fuel+tank+remove+video&rlz=1C1AFAB_enUS452US453&oq=1975+bass+boat+ranger+fuel+tank+remove+video&aqs=chrome..69i57.22730j0j4&sourceid=chrome&ie=UTF-8

Follow the fuel line from the tank towards the front. It should be in line at about the drivers door.

you need to set the meter by what specs are needed for the carburetor you now have on this truck. it is not noted here in your question

????? Was the dealer using his fuel tank or yours.Might be a blockage or contaminate in the fuel tank.Hope this helps

need more info, is it a center console? most sea pro boat 21.5 model the fuel tank is ether under the floor or under the console. both styles will have a manufacturing label on the fuel tank that list capacity. on a boat with the tank under the floor there will be service port holes so you can replace the fuel sender units. locate this service port hole and look for a label on the tank.

Check the fuel pump in the tank ,if it has a connector it could be heat burnt ,or the flexible connecting pipe from the pump to the outlet connection is loose ??

I had something like this before. There is a fuel saftey switch near the gas tank right by the rear end. Its a roll over sensor and mine fell off the mount and I guess the truck thought it was upside down :)

i did 155 on a tank Sunday, light came on at 125 and the gauge shows 1.6 gal left ( but don't trust it!!) I usually fill around the 150 mark and it takes about 14 litres. this assumes you've got a full tank which takes a bit of doing on a multi and if you get an air lock you can run out at 120 or less