Bit of help please guys.

1986 2.25 petrol 90.
I changed my mates tank for him yesterday, took the 90 for a local spin and all ran well. I put 2 gallon of fuel in and my mate put another gallon in when he picked it op.

He just called me and said he managed 40 miles and it conked out!
Left it for 5 minutes and drove for a while and conked out again.
He managed to get it home-just.

It sounds to me like its running out of petrol, maybe as its going round bends the stack/pick up pipe is not getting fuel?
I told him to stick another £20 of petrol in and try that.

Any ideas?