Wow... all you gotta do is read the TM

[pfarber]

I hijacked this off another CCKW site... simply because of the almost total lack of usable responses:

My truck had been running fine until I reconnected the hydrovac. It had been totally disconnected before by the previous owner.

There are two gaping holes in the intake system when the vac is disconnected. One if the vacuum check valve.. the other is the PCV valve. You cleaned the check valve... but does it seal 100%? Any air leaking by will disrub the air/fuel ratio. So you have to things to repair/replace... PVC and check valve. Also, the windshield wiper suction must be plugged or hooked up to a working wiper motor.. or that another big air leak. The shade tree test is spray water at possible leak points and see if the idle/backfire improves.. the water will temporary fill the leak (unless its very, very large) and allow you to pinpoint the general area.

Now it will run, but only on full choke. When given gas it backfires badly. Obviously I have some sort of vacuum problem.

More correctly its an air/fuel ratio problem. You are letting in to much air AFTER the carb. Cracked intake, but more likely the brake system. If you read the TM is will show proper servicing. Another question is it backfiring out the tailpipe or the intake?

I checked the air cleaner on the firewall. It seems ok. No dirt and oil was in the bottom.

That is the hydrovac vent. It will cause some brake release issues, but unless your vac is an empty tube is should not affect the engine.

I cleaned the check valve. Not very dirty

Again, a clean valve does not equal a sealed valve.

Any other suggestions?

yes, read the TM. The rest of the post talks about bleeding the brakes. They neglect to state that any bleeding MUST START AT THE HYDROVAC. I cannot believe so many people missed that. Its in the TM. Illustrated. TM9-1827B on this site has even more details on brake bleeding. If you do not start at the vac you are just pumping fluid out the brake cylinders.

Just goes to show there are popular web sites, then there are sites that have actual information.

[WWII TRUCK]

Hopeless owner, the truck will be deadlined more than operational.