I would check your lifters.  There were some bad ones going around a
couple of years ago (Italian) that didn't have a good surface hardening
and the part that pushes against the cam would wear away.  If you find
inordinate amounts of wear on your lifters I would replace them all and
start over.  You can usually tell the evil lifters.  They are about 1/16
to 1/8 of an inch shorter than a new one.  Some times they will wear so
much that they wear a hole into the middle of the lifter and then they
will never pump up again.  I just went through this with one of my
brother-in-law's campers.  Had to use the collapsible push rod tubes and
new lifters all the way around (and one push rod).

Hope this helps,
Ken Wilford
John 3:16
www.vanagain.com

Nate Saylor wrote:

> My '84 Westy has been driving fine (for a car that won't hold tune
> particularly well) lately.  Yesterday I went for a short drive and about
> 5 mins into it, it sounded like the engine was banging around when I
> would give it juice.  When I would let off a bit it would subside but
> the engine still sounded bad.  I limped home and started it today,
> taking it down the street for a test drive.  When it got warm it started
> making the noise again when I would try to give any sort of
> accelleration.  On further listening I found that it was rapid
> backfiring, not engine noise (my engine is pretty noisey anyway).
>
> Pertinant details:
>    Engine backfires rapidly under load when warm
>    Engine fairly quiet (not backfiring) when cool.
>    Engine has new heads (AMC)
>    Engine will not hold tune particularly well
>    Valves are clearanced per boston bob
>    Engine likes to turn rich a while after being tuned (hence won't
> hold tune)
>    Engine has some minor exhaust leaks (but I doubt they could cause
> anything this serious)
>    Lifters are pretty noisey (even for a clearanced top end).
>
> I suspect:
>    Cat gone bad from running rich
>    Temp II gone to hell and doing something wierd to the mix when hot.
>    Collapsed lifter(s) as valves won't hold adjustment very well.
>
> Please god don't tell me it's:
>    Burned valves, cause I'm just NOT going to go back into that engine
> again (Subaru here I come).
>
> Need help soon as I've got a pretty good commute to work and my westy's
> my only transportation (hello Hertz).
>