Quote:
Originally Posted by warren brown
I performed an autopsy on the filter with a hacksaw - and wow....
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Well done Warren, it's always pleasing to prove the fault, esp. with tuning problems which can be tricky to isolate. Generally we simply replace everything without learning the precise cause.
Just to expand on the diagnosis - I believe your CMP was suffering from Sceliphron caementarium - commonly known as the mud dauber wasp! It so happens my F15A suffered this particular ailment when it first hit the road. It drove perfectly well until I filled the fuel tank at the servo, which would have been the first time in many years, and must have dislodged a mud wasp's nest adhering to the upper tank area. After that it lost power up hills and could barely hold top gear on the flat. Like your truck Warren it was an older restoration which had been stored for many years, and since I lacked confidence in the restoration I fitted an inline filter initially, in case the tanks hadn't been cleaned out properly. As you can see the brand new filter was already badly clogged, which confirmed my fuel starvation diagnosis, and I was able to identify the culprit by comparison with a mud wasp's nest, of which there were many throughout the vehicle. Mine were built in Northern Victoria, whereas yours appears to be Riverina red variety!
The moral of the story in my case is never trust a previous "restoration". Both tanks had undergone extensive solder repairs to the usual rust holes beneath the tank straps, but apparently no attempt had been made to remove the rust from inside the tanks! Obviously the wasp's nests appeared much later during storage, and having taken the precaution of fitting an inline filter I discovered the nest in the fuel tank purely by accident. Likewise in your case Warren - assuming it's a mud wasp nest as I suspect, then without a filter the fine red dust may have passed through the carby unnoticed, because it's thoroughly dispersed in the fuel, as seen in the cloudy sample below. Much of it would be expelled through the exhaust, but some of it would inevitably pass into the engine oil, where who knows what havoc it would wreak on soft white metal bearings.
The upshot here is that by causing fuel starvation, our cheap plastic fuel filters alerted us to a potentially serious problem - Sceliphron caementarium! These critters are definitely bad news, and not just for CMPs. They've even brought down commercial airliners, by building mud nests in pitot tubes. In one case in 1996 the death toll was 189: "Investigators believe a colony of black and yellow mud daubers got into the tube and built their cylindrical nests inside, causing faulty air speed readings which were a large part of the crash. This species also brought down another plane in Washington during 1982."
Now that I've thoroughly cleaned out my tanks and lines I'm no longer running a fuel filter, but in light of these encounters with Sceliphron caementarium, it's even more imperative with fuel tanks of unknown condition. Rust flakes will merely cause fuel blockage, but any mud nests present could potentially ruin a motor, and we'd never even know how it happened!
On a proper resto of course I'd be using an original filter, however I'd probably use a paper element, because I believe they provide much finer particle filtration, by virtue of microscopic packed fibres. Certainly they're standard in critical applications like engine oil filtration. The downside of course is they're prone to clogging, as seen with these inline filters, including Phil's example. I suspect that would rule out paper as a fuel filter medium in WWII military application - even a large paper filter may clog quite rapidly on fuel poured from POL cans during a Libyan dust storm! The packed shim filter may reduce engine longevity in such conditions, but that's hardly a consideration in wartime, and certainly preferable to constant stoppage in convoy to replace clogged paper filters!