I have an '87 Pickup 22R with a 34/34 weber carb. I got a new gas cap about a month ago and I started getting what seems like vapor lock. The car stutters and jerks, mostly on the highway, but also other times at speeds around 35mph+. Once it starts stuttering, I can let go of the gas and it smooths out, but as soon as I hit the gas again it jerks like it's sucking air.

I can pull off the gas cap, and it seems to run perfectly. Is this a normal symptom of vapor lock, or should I be looking for another problem? I'm worried my carb might be the issue, but I'm not sure how to troubleshoot that.

I replaced a leaking fuel pump (mechanical) a couple months ago, and the fuel filter about a year ago. My carb is about a year and a half old -- my dad helped me install it, but I wouldn't say I know a whole lot about them.

Could be clogged fuel tank vents making it hard for the pump to get fuel out of it

Might also check the fuel filter again, I once got a dirty batch of fuel in my old FJ55 LandCruiser and it had exactly those symptoms. With the filter out, I could hardly blow through it. New filter and it worked fine.

And on the vents, might also check the charcoal cannister to make sure it is working properly, as that ties into the venting system.

Where can I find the vents?

Are the charcoal cannisters even used with a Weber Carb?

The biggest thing that confused me when I installed my new carb is how all the emissions gear fits together. The weber carb uses none of it, while the stock carb was a rat's nest of vacuum lines. I left most of it intact. I've wanted to rip stuff out and replace my EGR with a block plate, but I'm afraid to mess anything up.

A Factory Service Manual would show the vacuum connections. The gas tank vent line connects to the charcoal cannister up front (usually passenger side firewall location) and from there a purge line runs to the intake where vacuum sucks out excess gas fumes.