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Rubber Change - Carb Debris


Rogerck

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My replaced line was a Gates fuel injection line. I bought a replacement for that one from Auto Zone and it was exactly the same product according to the nomenclature printed on the hose but it did not have the flaking problem that the one put on during the rubber replacement had.

However, both of them when immersed in car gasoline turned the gasoline black in a few minutes. It was not the inside of the hose doing melting but the outside and then when removed from the gasoline the outside was sticky. So much for fuel injection line.

I replaced with regular 1/4 inch fuel line (low pressure) since it is not a high pressure requirement.

Much flushing was necessary since there is a return line that re-enters the top of the gasgolator and therefore there is crap gets back into the top of the gasgolator on the filtered side of the gasgolator that returns to the input side of the fuel pump which hopefully is filtered out within the fuel pump....ans so on....a real pain in the butt.

Larry

N255CT

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  • 2 weeks later...

Follow-up situation report:

 

About two weeks after the hose change-out and the addition of the inline fuel filter we are having no further debris issues, and nothing is showing up in the filter. That's the good news. The other not-so good news is we are finding the fuel drained from the gascolator sump is sometimes discolored. Instead of the usual yellow color of unleaded premium, it is a brownish-orange. This seems to occur only after the airplane has been sitting for awhile. We presume that this discoloration is coming from one of the other fuel lines. The question is which one. We replaced the return line (the only hose we were sure was 1/4 inch) but not the others, which we presumed were the 5/16 hose, and which didn't seem to be having the deterioration issue.

 

Are any other hoses on the top of the gascolator 1/4 inch? Any thoughts as to where else might this issue be coming from?

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One more item, now that I have had this continuing problem, (I think it is solved) I sump the gas into a plastic container like a cottage cheese container that is white. I also sump about a pint at least and the put it in my truck. In the white container it is easy to see any contamination and also to observe the color. At first I was getting some small specks in there but after draining several samples it would become clean. I had to assume that the small specks were coming from the return line that empties into the top of the gasgolator above the screen but they were so small I assumed they could get through the screen. Don't know! Finally I think I am OK since the last couple samples were crystal clear but I am still fighting with getting out in the boonies with the plane until I regain confidence that it will not happen again.

Larry

Flying Bozo

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round_peg,

The discoloration that I experienced was from the outside of the rubber hose. When it was subjected to the auto gas (on the outside) it began to melt and turned the gasoline black with agitation. Not only did the hose replacment do that but also the one that I then purchased at Auto Zone. Both of them were Gates brand fuel injection hoses. The only thing different was that the one I purchased at AZ didn't have the flaking on the inner part of the hose. In any event I didn't replace it with that one but put on a regular fuel line hose since there is not high pressure from the fuel pump to the carb. This regular fuel line hose did not show any signs of melting or getting soft like the fuel injection hose.

I can't shed any light on the reason you are experiencing the discoloration in your fuel.

Larry

Flying Bozo

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  • 6 months later...

I flew back from Las Vegas today. While climbing at full power over the Sierras in light turbulnece, the engine power dropped way off, below 4000RPM. I moved the throttle to idle and back so whether that did it or not, it cleared up after ~3seconds as if nothing had happened. It was a very long 3 seconds. I looked at the EFIS and just the Right side EGT had fallen away to 600deg or so and then sprung back so I pretty sure the R carb got jammed, cutting off fuel to 2 cyliners and then passed whatever was plugging it. I had hoses done about 8hrs back so maybe I got some debris too. Very unpleasant event.

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I flew back from Las Vegas today. While climbing at full power over the Sierras in light turbulnece, the engine power dropped way off, below 4000RPM. I moved the throttle to idle and back so whether that did it or not, it cleared up after ~3seconds as if nothing had happened. It was a very long 3 seconds. I looked at the EFIS and just the Right side EGT had fallen away to 600deg or so and then sprung back so I pretty sure the R carb got jammed, cutting off fuel to 2 cyliners and then passed whatever was plugging it. I had hoses done about 8hrs back so maybe I got some debris too. Very unpleasant event.

Yikes... not fun. Did you happen to observe the fuel pressure during and/or just before this happened? Could be carb debris, but vapor lock is another possibility. Happened to me on my second solo flight. :o You could tell which it was if you saw what the fuel pressure was doing (vapor lock causes a drop in fuel pressure... carb debris shouldn't).

 

-Russ

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It was hot since I was climbing out of Lone Pine. I didn't look at fuel pressure in the moment but I often get a low fuel pressure alarm climbing out from places like Tuscon with a hot engine. I thought this was just a failing of the sender when it gets very hot since it sits right on top of the engine. I've had the sender replaced and they both do it. It has never made a carb hiccup like this before though. So maybe it was a vapor lock bubble that cleared itself. It was abrupt both start and end and did not repeat.

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It was hot since I was climbing out of Lone Pine. I didn't look at fuel pressure in the moment but I often get a low fuel pressure alarm climbing out from places like Tuscon with a hot engine. I thought this was just a failing of the sender when it gets very hot since it sits right on top of the engine. I've had the sender replaced and they both do it. It has never made a carb hiccup like this before though. So maybe it was a vapor lock bubble that cleared itself. It was abrupt both start and end and did not repeat.

 

Based on the proximity to the hose replacement work, I'm going to guess that you had rubber debris in the float bowl. Actually you might still have debris in the float bowl. The experience we had is that even some tiny pinhead-sized bits accumulating can cause the fuel flow issue at full throttle. Others have found that the blockage clears temporarily by throttling down and then back, and this sounds exactly like what you did. If so you aren't clearing the debris, just moving it around inside the bowl. If I were you, I'd look inside those float bowls. We had to change out all of our hoses to make this issue go away.

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SO now I'm not sure whether I was vapor locked or had some debris. I called Jeremy since he did my hose change but we did look at the bowls after a couple hours of flight and they seemed fine. How many of you hot zone pilots have had vapor lock before and does it generally just clear itself after a few seconds? I could have glided back this time, but from a practical side, once you are over the ridge (near Kearsage pass this time) from the east, there is no way to glide to a good flat area unless you are up at 16K feet or so. I've crossed the sierras about 50 times in my flying life, including about 14 times in a Tomahauk, which is much more of a challenge than the CT. The CT can climb to well over 14K. You basically need to ride the mountain waves like a glider pilot to even get the piper above 12.5K especially when you start from the eastern valley. I would often go mountain climbing out of Independence or Lone Pine.

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How many of you hot zone pilots have had vapor lock before and does it generally just clear itself after a few seconds?

I have had it happen four or five times, always with mogas, mostly with mogas containing ethanol. (One time it happened with mogas that was ethanol-free AFAIK.) The other common denominator each time was that I had first run the engine, then shut it down for a short time, and then started it back up again. After restarting, the fuel pressure would waggle around erratically, and drop below 2psi during a full-throttle run up. I never had the engine stumble while on the ground, but on climb out the fuel pressure would sometimes drop to zero. After a few seconds, the float bowls would empty out and the engine would abruptly lose power.

 

Throttling back always kept it alive... thank goodness, since a couple of times I was at a few hundred feet after takeoff with mediocre landing options. :o

 

I switched to avgas and have had zero trouble since. (Not trying to start an avgas vs. mogas debate here... just reporting observations. :))

 

-Russ

 

P.S. Carb debris was checked for thoroughly, even to the point of rebuilding both carbs. Some flecks of hose were occasionally found, but none of this made the issue go away... only changing fuel did.

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That's pretty interesting. The fuel pressure had been waggling on the long climb up from the hot valley and I was on Mogas. I also was thottled back for awhile after that event and there were no further hiccups. Seems like vapor lock is a more plausible explanation although I was sure it was debris at the time. That's the trouble when you think you know the problem, you stop looking for other things. I didn't even know about vapor lock as a serious potential issue with the CT before now.

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P.S. Carb debris was checked for thoroughly, even to the point of rebuilding both carbs. Some flecks of hose were occasionally found, but none of this made the issue go away... only changing fuel did.

 

It is quite conceivable that the ethanol content in mogas promotes flaking in the hoses, but I don't think running the engine on fuel that it wasn't designed to use is the ideal solution. Based on our experience with the flaking, it is an issue connected to the fuel line material. When we replaced all of our fuel lines with Gates Barricade, both the flaking and the chronic fuel discoloration issues we were experiencing vanished. Also based on our experience, if the engine loses RPM I would absolutely drop the float bowls and look for rubber debris and not assume that it was a transient issue such as vapor lock.

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I did some more research. High Vapor pressure and resultant vapor lock is a well known concern with E10. In fact, most STC attempts for GA aircraft, when they fail, fail during vapor lock testing

http://www.eaa.org/autofuel/autogas/articles/1Autogas%20vs%20Avgas.pdf

Makes sense since Ethanol has a BP of 78C while AVgas is more like 100C. In hindsight, I don't think the fuel pressure sender is flaky. It bounces around as bubbles go gurgling by. I wonder if remote mounting the sensor would just end up masking these swings. The description in the EAA article makes me a perfect candidate for lock. High, hot, extended full power climb.

I had just gotten blithly used to dealing with a swinging fuel pressure in hot climes during climb out. It's what the NASA engineeres studying the Columbia accident referred to as the Normalization of Deviance. I plead guilty. OTOH, FD says nothing about vapor lock and ROTAX only very briefly mentions in their operators manual to use AVGAS if vapor lock is an issue. During my annual Jeremy mentioned he happened to just have had a bad batch of MOGAS (losing power) he had to drain and replace. Mid summer in Tracy, CA can get pretty hot so I wonder if he didn't have lock issues as well. Russell nailed it but I don't think many CT pilots or mechanics are even aware of this one.

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