FUEL GAUGE ISSUES, NEW SENDER BUT GAUGE STILL INACCURATE Options

[OLAF]

I'm stumped. '71 model 914. Verified Gauge is working properly and New Sender Unit.
Problem: my fuel gauge reads only 1/4 tank when the tank is full.

I pulled the sender and bench tests indicated the float sticking. I bought a new one from Stoddard. $100.

I also pulled the gauge and bench tested it at 12v to the "+" terminal with ground to terminal 6 and terminal 4. The gauge needle pegs to "full". It's working properly.

Prior to installation of the sender into the tank, I attached the New Sender to the harness and with the ignition on, moved the sender through upright and inverted positions, (simulating an empty and full tank). The gauge needle swings as it should through "empty" and "full" readings.

Once the sender is installed in the tank however, it only reads 1/4 full (although the tank is full).

I surmised that the Float in the New Sender wasn't moving in the tank due to less then adequate adgitation in the sender cylinder (it's vent holes are small). So I removed the innards of the sender and drilled several holes through the cylinder as a remedy.

Retested the sender out of the tank and the gauge swings empty to full as it should.

Installed the sender in the tank. But, the gauge still reads only 1/4 full.

I removed the sender and bench tested it in a bucket of water and can see the float moving easily through the new large vent holes.

Why will the gauge work properly when the sender is outside the tank but not work when the gauge is installed into the tank??

THANK YOU ALL for your suggestions... I'm Stumped

Sorry, my photos are "too large" to be attached. I don't know why...

[914Sixer]

Did the NEW sender come with a pin installed at the side toward the bottom? Has to be removed to release the float. Under yellow label in picture

[fixer34]

Have to ponder the gauge issue, but might be able to help with pictures issue.
Most phones now take very high resolution pictures. However that makes the picture size very large.
Download a free program called IRfanView. Open one of the pictures using that program, then save it as a jpeg. The size should be much smaller and will upload.

[OLAF]

Did the NEW sender come with a pin installed at the side toward the bottom? Has to be removed to release the float. Under yellow label in picture

Thanks for the reply. You asked "did I remove the pin which prevents movement of the float prior to installation"? Answer: Yes, and I agree, that should be the first thing done.

[Chad911sc]

Could be getting caught on something in the tank at about 1/4 full. That would be the only explanation that I could think of.
If you need help on this site, there are Many who will help you. But it’s Always easier with pictures.
This is step by step how to shrink your pictures to fit in this site. If you do this you can send 10 pictures or more on one post.
This is for IPhone, so hopefully you have one.
Open your pictures, tap send.
Send to files.
Open files and hold your finger on the picture you want to post and pick quick actions.
Pick convert image.
Tap jpeg
Tap large.
After you do this the picture can be sent by the choose file and add attachment at the bottom of this page.

[fixer34]

Have to ponder the gauge issue, but might be able to help with pictures issue.
Most phones now take very high resolution pictures. However that makes the picture size very large.
Download a free program called IRfanView. Open one of the pictures using that program, then save it as a jpeg. The size should be much smaller and will upload.

Sorry, forgot to note you need to transfer the pictures to your computer to use the above program. Also allows you to easily crop/resize if needed.

[fixer34]

Agree, very unusual.

Is there any way to block the float at or near the top (so gauge shows full), then gently lower the gauge into the tank and make sure it still reads correctly?
Since the cylinder is basically sealed and you have proven it moves freely, that pretty much rules out mechanical interference.
Almost like an electrical issue where seating it in the tank adds extra resistance.

Do you have an ohmmeter/multimeter by any chance. Take resistance readings from the G pin to the ground terminal with it out of the tank, both 'empty' and 'full'.
Put the sender in the tank, check the resistance reading again. Do not connect the cable/plug or turn the ignition. Does the resistance reading match full of empty/quarter full?