my trucks acting wierd

[87swb]

OK here goes:
-i have an 87 305 TBI with dual tanks and dual fuel pumps
-when it's on the left tank it cranks and runs bad, most of the time in the cold weather and then when it warms up it runs better
-when it's on the right tank it cranks and runs good, no matter the temp. cold warm or hot outside
-the other day i had it on the right tank and have been driving it on the right tank because for some reason when its cold outside and i'm using the right tank it runs better than the left one, anyway the other day it wouldn't crank on the right tank so i had to switch it to the left one and it cranked up so i switched it back to the right one and it kept on running fine
-i thought it might be the fuel pump on the right but i took the fuel line off behind the tbi and cut the key on and gas was shooting out

does anybody know why it's acting like this??? btw sorry so long and confusing but please answer, thanks

[ChevyGuy]

The switch isnt closing all the way when on the left but on the right it is or you have alot of trash and water in the left one.

[VileZambonie]

What do you mean it cranked?

The presence of fuel isn't good enough. you need to check your fuel pressure. Take the fuel filter out (good time to replace it and check your fuel pressure with a fuel pressure gauge. you can buy one pretty cheap at autozone. Compare your results from tank to tank.

[87swb]

sorry what i meant is it cranked, started up and ran fine