As the topic came up in another thread, I figured I would discuss the topic of fuel handling.
First and foremost, there should never be any “buildup of debris” in a needle valve over time, and if that happens frequently, you have a fuel contamination problem. You should not have to routinely clear it out.
As it comes, any quality name-brand fuel I have used over many years has had practically no contamination, and by that I mean, I have found at most a few little specs in various filters after dozens of gallons. David F. used to dutifully filter every drop of fuel he used through coffee filters, decanting it from the factory jug to a “use” jug, and I did it for a while, too, even though I had never had an issue. While I was doing the coffee filter routine, I would periodically get little threads that would get stuck on the needle or in filters, and I had to disassemble and clean it out about once a gallon or so. I switched to some 10 micron stainless steel filter material that I “acquired”. Had there been any contamination, this extremely fine media would have quickly clogged up, and anything smaller than 10 microns would pass easily through the needle valve. I did this for maybe 20 gallons of fuel, never once did it filter out even a speck of contamination, and while it later got clogged up with dried-out castor oil (cleaned up with lacquer thinner…), it still passes fuel easily. Point being, with either SIG, Powermaster, and Byron, I never found anything at all.
Now, of course, I stopped filtering it by decanting through a filter because it was unnecessary to eliminate non-existent contamination, and greatly increased the exposure to air.
I use the DuBro plastic/aluminum “kwik-fill” fuel can fittings:
https://www.dubro.com/collections/fuel-accessories/products/kwik-fill-fuel-cap-fittingThis has only plastic and aluminum parts, and the fuel “probe” seals air-tight with an o-ring. It seals well enough that you can leave the fuel in the back of the car and it will hold the pressure of temperature changes without leaking, so it doesn’t “breath”. The aluminum and plastic last forever in the presence of fuel. The similar brass version doesn’t seal up, and, will definitely corrode away under the presence of methanol vapor – that’s what happened to mine, it just fell apart one day. It also has large-diameter fuel passages and uses the large tubing for the up line, so you can suck it up much faster.
The kit comes with a pickup with a coarse nylon screen in the pickup. I use that, a “Russkie” take-apart filter with a medium metal mesh, and then the larger of the two Sullivan “Crap Trap” filters, with a medium and fine filter. All the fuel is sucked through the filters on the off chance that something gets into the fuel from handling it. This just goes onto the plastic cap from a Powermaster Can. Note that you want to use a *metal can* like Powermaster comes in – fuel is definitely sensitive to light and will break down after a while. Additionally, plastic eventually gets brittle and can crack as it is cycled with temperature, so you end up with a car trunk full of fuel. The same could happen with a metal can, but so far, it hasn’t.
https://www.amazon.com/Sullivan-Products-Double-Screen-Filter/dp/B0006O8MPAI use a 5 ounce veterinary syringe with a replacement nylon stopper that I got from the late Carl Shoup. Jim Lee makes something similar. My syringe body is a “catheter tip” with a large conical end where the fuel comes out, as opposed to the “lock” type intended for use with a hypodermic needle. The original black stopper will work for a while, and while it is clear that the rubber breaks down and leaves black marks on the inside, I haven’t found any real problem with it. The big problem is that at some point, the plunger will pull out of the rubber while you are sucking up fuel, and pull it sideways and all the fuel will go on your pants ,airplane, the ground, etc. the same thing happens when the o-ring breaks on your Carl Shoup stopper, but that was once in the last 30 years for me, rather than once a month for the original stopper.
My syringe fill tube has a “crap trap” filter in it, but it ends up not really filtering anything because it has two-way flow. It’s just there to transition from the large to the small tubing. If anything came out of the fuel can, it would get pushed up against the fine medium and then pushed into the tank when I got to fill it.
In the airplane, I use a single Crap Trap filter in the pickup line. Over the years this does catch a speck or two now and then, and the occasional “thread”. Part of this comes from solder rosin on new tanks, and part of it is various dirt and insect parts. I inspect it once a year when I clean up the inside of the cowl before the NATs. Again, only occasional specks, now and then.
In some situations, the Crap Trap is too long to fit. For that, I use the very small take-apart filters sold by Dave Shadel, Dub Jett, and others. They are the same OD as fuel line and use just a tiny chip of medium-fine filter media. The issue with these is that they can come loose and then leak air. I always clean them up, then apply a VERY VERY THIN layer of silicone sealant on both sides of the gasket, then screw them down as tight as I can manage with my fingers, holding the small end with pliers. DO NOT get any sealant inside the filter.
Note that both the Crap Trap and the various take-part filters have a “inlet” and “outlet” side. On the Crap Trap, of course the medium filter comes first, then the fine. On the take-apart filter, the externally-threaded side comes first, and the “hollow” inside-threaded part is downstream. This puts the filter media on the engine side rather than the tank side, so if large debris does get stopped by the filter, it can build up in a large-cross-section area rather than the small tubing nipple. At least on my 40 and 60-sized engines, the medium on the Shadel filter is small enough that if something can fit through, it can also fit through the needle. You don’t want it any finer than necessary to avoidl the possibility of unnecessary clogs.
And no matter what anyone might tell you, I urge to you to ALWAYS, repeat, ALWAYS use a filter in the airplane. The usual beef is that having a filter means you can have an additional chance of air leaks. That is *exceedingly rare* and can easily be dealt with. The only time I have seen a Crap Trap leak is due to a manufacturing defect, when the push the aluminum end fitting in, I have seen two them where the clear plastic got tucked under and caused an air leak. It is easy to see just by looking at it, screen for it. The take-aparts and “disposable” types can leak through the joint. The take-aparts are treated as I described above. The little blue disposable types need something done. Ted used to use “plasti-dip” toll grip dip medium, which is some sort of liquid vinyl. Flex seal would also work – just paint a thick layer over the barrel of the filter. Regardless, even with the most careful handling, you can pick up insect parts and dirt during the launch and in flight, you must stop these at the filter, it cannot be allowed to get into the needle and ruin a flight, burn up the engine, or cause a crash.
Assuming you do all this, your incidence of unexpected changes in the engine run (outside an intentional change you made, or the usual altitude/temperature/humidity variations that are generally very small) should be rare. But, suppose you *do* find a problem, where it suddenly seems as if you need to make a huge adjustment to get it to sound or tach right, or it “takes off” lean in the middle of a flight. You can sometimes “fix” these clogs by opening the needle a lot to try to let the debris go through the larger opening, and then turn it back after. But I would only recommend that in the case where you are down to your last competition attempt and have no other choice.
In any other case, I would very highly recommend killing the engine, and taking it apart to inspect the fuel lines for splits, leaks, check all the filters for debris. But most critically, remove the needle completely, wipe it with your finger, and then run a small “bottle brush” through the spraybar with acetone or some similar solvent. You can get very small bottle brushes or “tooth gap brushes” at a drugstore, for going between your teeth. Then flush it with fuel. The reason for physically cleaning everything is because if one of the mysterious threads gets wrapped around the needle or stuck in the spraybar, it can withstand a simple flushing and get stuck where the end of the thread gets pulled into the spraybar hole or spigot, and the free end whip around inside the venturi. This tends to give wildly unpredictable effects, and the fuel will run down the thread sometimes and then back onto the venturi walls, or something odd like that. You need to clean both the needle and the spraybar with some mechanical action to assure you will get it.
This all sounds kind of paranoid, but over the years I and many have learned the hard way that it’s no paranoia if mystery debris really is out to get you. You cannot be too careful about this stuff.
Brett
Topic: Fuel Handling (Read 1495 times)
