wrote:
>
> I now know not to pour through the carburetor. That IS the method
> described in the instructions on the can of Sea Foam. They say it's
> also possible to use a vacuum line, but the carburetor is mentioned
> first. Maybe they should change their directions.
>
> My truck doesn't have power brakes or A/C. Any other recommendations?

As was previously mentioned, an EGR or PCV valve.

Its possible for a good backfire to jam or otherwise bugger up the
internals of things like PCV valves. This will cause a vacuum leak, but
not to the outside world. This will make detection more difficult, as
the leak will not be audible.

One way to diagnose such a problem is to locate each hose feeding into
the intake manifold and, with the engine idling*, pull it off. If the
engine lugs own or stalls, it probably wasn't part of the leaking
system. If the engine RPM remains constant, try plugging the port into
the manifold with your finger. If the RPMs pick up, that could be the
leakage path.

*if the idle is already rough, adjust the speed up first with the idle
speed setscrew rather than having somebody step on the throttle. This
technique depends on a consistent throttle/idle setting.

--
Paul Hovnanian
------------------------------------------------------------------
The ark was skippered by amateurs, the Titanic was skippered by
professionals.