1991 PCM 5.8 backfiring problem

1991 Nautique Excel 351 Ford PCM engine; Motor will idle and run below 2000 rpm most all the day, but when run harder will intermittently start backfiring in the carb repeatedly and loosing power. Has been in several shops over three years' time without being fixed.
Any suggestions? One dealer suggested a complete PCM "Pro Tec" engine management system upgrade, blaming the 1991 version as beeing prone to similar problems all along.

Could a weak fuel pump cause carb backfiring?
Any other suggestions? I can manage nearly any diagnostic suggestions that can be offered.

Tom
Lake Lanier, Georgia

I'd check the timing first on any engine that's backfiring. If the engine idles OK and then backfires when you hard throttle the timing advance is not working. Either that or the timing chain is getting sloppy.

The most important post on the other "thread" was SS201...IMO if you have an engine that's 10 plus years old...make damn sure the timing chain set is working or your gonna throw thousands at new ignitions etc. A new chain and gears are about $50.

After a few backfires, the Holley is known to rupture the Power valve and both the power valve and timing can be replaced and checked in short order by yourself or a mechanic.

The base timing for the 351 Pro-tec engine is as follows:

Std: 18 deg. BTDC @ 700 rpm, 30 deg @ 3600 rpm
HO: 18 deg BTDC @700, 26 deg @3600 rpm

You MUST remove the knock sensor wire to accurately set the timing. Removing the wire disables the cruise mode which is present at idle. Cruise mode advances timing when no throttle movement is detected after 30 secs.

I forgot to tell you make sure the knock sensor wire is connected before you check it at 3600 rpm.