Truck stalling out after switching to primary tank

[71threequarterton]

This seems to be happening every time I switch from the auxiliary tank back to the primary tank. I've had the truck for maybe a couple months or so. It was a long trip to drive it home when I bought it so I filled up one of the auxiliary tanks and ran off that for a while once I made it back home. When I switched back to the primary tank the truck stalled and I had a hard time getting it started back up again. That was probably about a month ago. Once I got it back up and running, I've been driving ever since with no problem, running off the primary tank. I made another long trip a couple weekends ago and ran off the auxiliary tank again until today when I filled up the primary tank again. So I switched back over to the primary tank and it's stalling out on me again. Any idea what's going on here? I'm currently having trouble starting it and running off the primary tank.

[Stocker]

Non-vented gas cap where it should be vented? Or fuel pickup in that tank is blocked with crud? Pinched / crushed / rotted fuel line?

[LongBox]

If the primary tank sat unused for a long time, it might have rust or varnished gas in it. That would block up the "sock" on the pickup, and might also send rust and crud down the line. It also may have an inline filter in the line under the cab. That could be clogged.

[71threequarterton]

Originally Posted by Stocker

Non-vented gas cap where it should be vented? Or fuel pickup in that tank is blocked with crud? Pinched / crushed / rotted fuel line?

Pretty sure I have the right gas cap but I'll check all that stuff out.

[71threequarterton]

Originally Posted by LongBox

If the primary tank sat unused for a long time, it might have rust or varnished gas in it. That would block up the "sock" on the pickup, and might also send rust and crud down the line. It also may have an inline filter in the line under the cab. That could be clogged.

I follow what you're saying but I only ran off the auxiliary for two weeks(not daily driving - I drive it a few times a week). Doesn't it take a long time for gas to varnish?

[Stocker]

Originally Posted by 71threequarterton

I only ran off the auxiliary for two weeks(not daily driving - I drive it a few times a week). Doesn't it take a long time for gas to varnish?

A lot longer than a couple weeks. Even today's gas should stay good for at least a few months.

[LongBox]

I was under the impression that you'd only had the truck for a couple of months, and perhaps did not have knowledge of how the previous owner used the two tanks.

[71threequarterton]

Originally Posted by LongBox

I was under the impression that you'd only had the truck for a couple of months, and perhaps did not have knowledge of how the previous owner used the two tanks.

Yes, I have only had the truck for a couple months or so. Unless the previous owner was BS'n me, he said the auxiliary tanks worked fine and he used them. I've only used the one on the driver's side and it works fine - I can switch back and forth from the auxiliary and primary on the fly - actually did that on my first drive home when I bought it - no problem at all. But what I've noticed now, is the two times that I've run off the auxiliary tank for a while, as soon as I switch back to the primary, it stalls out on me. I'm gonna start out by checking the filters.