Short_Straw wrote:
Wernt we just talking about this like two days ago haha! Maybe I jinxed myself!

Oh crap, we did just talk about this! Is it my turn now?!

ok bad joke...
Short_Straw i'd say you got the long straw on this. (long straw=good)
good job

100LL has a lot more led than the 80-87 that was right for the 0-300. We put a hundred hours a month on pipeline Cessnas, but often had to clean the bottom plugs every fifty hours. If we did not, the engine would run poorly. I know there are problems with modern auto fuel, but I used it in the 0-540 engine in both Pawnee and Callair through the end of last century. O-540 is a slow turning, loose, engine like the 0-300.

I don't know if this will be a help or a hindrance.

In the approximate 600 hours on my engine since it was custom built after the first one cratered, a Lycoming O-360, I've only had one instance of a minor power loss. It came on the leg between OSH and DBQ on the return flight, a few years ago. The weather was humid--typical Wisconsin/Iowa in the summer. The engine started running rough, so I immediately pulled the carb heat, which seemed to help a little but not much. Then I did an in-flight mag check, and there was a significant drop on one of them (don't recall which). It didn't seem like any sort of pre-emergency, so I continued on to DBQ, refueled, and had lunch.

Because it was a Sunday and there were no mechanics at the FBO, I elected to find a nice clean area on the ramp and do a full power run-up, leaning the engine as I did it. On the mag check, initially there was an excessive drop on one of them again, but it cleared up within a few seconds. From then on, it ran smoothly, and still does. Trying to analyze what had happened, I realized that I had sat idling at OSH for a very long time, waiting to take off, and in all likelihood I hadn't leaned "aggressively" enough on the ground. I assumed, therefore, that a plug or maybe more than one plug had partially fouled, and some carb ice had aggravated the situation,

When I got home, I asked my IA about it, and his guess was a fouled plug or two, too. He said that if it had been an actual mag problem, that wouldn't have cleared up during that full power run-up at DBQ. A couple months later when he did my annual, he said that all of the plugs looked good, all properly gapped and none fouled by either lead or oil. But he said that lead fouling can happen and then be burned off and not show up again.

Normally for all ground ops, I "aggressively" lean at taxi rpms or less, and except for that one instance when I apparently didn't do it sufficiently, that has kept my engine from fouling the plugs.

So examining your plugs, all of them, should tell you something.

I have not had a fuel starvation problem in any airplane, but I have had that happen in both my motorhome and one of my cars, when our local gas station got some bad gas, causing both vehicles' fuel filters to plug. Changing the filters took care of it, although I also added some HEET to eliminate the water in suspension in the fuel. I regularly add HEET in the winter, too. You can't do that in a certificated airplane, but PRIST makes a similar product, to eliminate water in suspension in the fuel, and it's approved for certificated fuel systems. But if a filter has been clogged with moisture, you will need to change the filter first. Not being a mechanic, I have no idea what sort of filters or strainers, if any, are in aircraft fuel systems other than the gascolator, which is a strainer. I'm assuming that you've checked that for moisture and sediment.

Incidentally, if your gascolator is an original glass bowl variety, there's a good replacement, STC'd for just about every light single out there, by Steve's Aircraft. They're made from aluminum, very precision made. They're not give-aways, but to me a whole lot safer than having a glass bottle of fuel only inches from a hot exhaust. When I wanted one, my airplane was not on their AML, but rather than forcing us to go through the field approval/337 route, Steve's arranged to add mine to their AML. It was a simple swap out and install for my IA.

Cary

Okay...

So a mechanic and I started into it today and did't get to far. Took the cowling off gave it a once over and started it up, and to my worst fear it ran fine... I was really hoping to find a broken butterfly valve or something I could fix and not think about an intermittent problem.

next step is to clean and gap the plugs, but it looks like everything was in order, at least no major mechanical failure. Checked some other theories but they all seamed okay as well.

Ice seams to be a reoccurring theory, but it has flaws as well, the RPM drop was fairly sudden, there was no rough running leading up to it making my think to pull carb heat. I ran carb heat the entire glide (13 or so minuets) I wish I thought to feel the carb after landing but ya live and learn.

Any similar ice stories?

Other thoughts?

That has got be be frustrating. Hope you find something to get rid of the uncertainty.

My only other ice story was when I was a student, landing at Merrill Field in Anchorage in a 150. It was a relatively warm (20F) winter day near Christmas 1972 or the New Year, and I had forgotten to pull on the carb heat. As I tried to add power because it looked like I was going to land short of the spot I was aiming for, the engine just quit, and the prop stopped. I landed and tried to restart the engine, but it wouldn't. I pushed it off the runway by hand as several other airplanes had to go around. Within a few minutes, it did start, and after a thorough run-up, I called the tower to take off and return to Elmendorf.

Although you said you ran with the carb heat on for a lengthy time, you might want to make sure that your carb heat system is up to snuff. If the carb heat butterfly valve isn't fully closing, or if the heat muff is blocked, or if the tubing is loose, you might not be getting sufficient carb heat to prevent icing or to combat icing which has already occurred.

Incidentally, a carb temp gauge is a worthy addition. Mine was a $100 option on my Insight G1 engine analyzer. There are plenty of stand alone gauges available, too.

Cary

I have a steam gauge carb heat with probe for free if you want it. I lie 45 minutes south of ashland

Tim

I suppose it's unlikely that both fuel tank vents got plugged . . . but with plugged or partially plugged vents, an engine can sometime run for a good while until it starts loosing power, running lean etc. Landed my Husky in a cow pasture almost taking out a barb wire fence due to that.

I'd think a stuck valve would be hammering and shaking something fierce, not the smooth loss of RPM that you described.

As other's posted, it does sound like fuel starvation. If carbureted, be sure to check the finger strainer in the carb too, And the float to make sure it ain't binding or sticking.

bumper

I have been told that these old carbs are so simple that they either work or don't, with little intermittent issues, do you think that it would be worth taking it apart if it ran "okay" yesterday?

That day was also the first time I ran auto fuel rather than 100LL, is either fuel more susceptible to ice? other issues? or it that a non-issue and i'm looking to hard for a problem haha

If it was the first time you ran auto fuel, is there a chance that vapor lock was an issue. Pulling carb heat on an engine that's not making power and barely turning the fan does pretty much no good, there is not enough heat being made to melt out the ice.

Any chance there are baffles in your exhaust? I had one break out and close off the outlet and could only get 1200 RPM or so out of the engine... not enough to keep a pacer on floats in the air when I just broke the ground and was climbing hard to clear some trees....

Short_Straw wrote:I have been told that these old carbs are so simple that they either work or don't, with little intermittent issues, do you think that it would be worth taking it apart if it ran "okay" yesterday? ...

That's an overly-simple way to put it IMHO. Sometimes they just sorta work.
It's easy to check the strainer. Disconnect the fuel line at the carb, then remove the brass bushing-looking part that the fuel line connects to. There should be a finger screen on the inboard end of it. Make sure there's no crap in it. While you're at it, put the end of the fuel line into a bucket and turn the fuel selector on. Make sure there's a good strong continuous stream of fuel. Although I don't know what the flow rate should be, it might not be a bad idea to time how long it takes to fill up a gallon gas jug. A partially clogged line might look like it's flowing OK, but not delver enough fuel for proper engine operations.
There's also a screen at the gascolator, make sure it's clear. And some aircraft also have strainers at the fuel tank outlets.

What do you know about the auto fuel you used?

Was it run through a water blocking filter or any other filter, or just straight from the gas pump? Or was it from an airport source, which hopefully you can assume has better quality control? The reason I ask is because when I first started running auto fuel, I found one local station that sold ethanol-free fuel to have a lot of junk in their tanks, and I consistently found it in my transfer pump's fuel filter (transparent) bowl... so I switched suppliers and have been pumping clean fuel for over a year now. I'd hate for that crap to be clogging up the fuel strainers.

Short_Straw wrote:...That day was also the first time I ran auto fuel rather than 100LL...

akavidflyer wrote:If it was the first time you ran auto fuel, is there a chance that vapor lock was an issue....

Reminds me of many a conversation with customers back when I twisted wrenches for a living. Let them talk long enough and they eventually told me what really happened.
Bingo! That's where I'd place my bet.

Cary wrote:I have not had a fuel starvation problem in any airplane, but I have had that happen in both my motorhome and one of my cars, when our local gas station got some bad gas, causing both vehicles' fuel filters to plug. Changing the filters took care of it, although I also added some HEET to eliminate the water in suspension in the fuel. I regularly add HEET in the winter, too. You can't do that in a certificated airplane, but PRIST makes a similar product, to eliminate water in suspension in the fuel, and it's approved for certificated fuel systems.Cary

Au Contraire... Isopropyl Alcohol is also an approved anti icing additive approved by the FAA for use in reciprocating aircraft engines. To qualify, the alcohol must be 96 % or more IsoPropyl Alcohol.

Here's a link to the MSDS for ISO-HEET: https://www.imperialsupplies.com/msds0055120.shtml

Note that this stuff is 99 % pure IsoPropyl. ISO-HEET is the stuff in the RED bottle, not the regular HEET product, which is in a yellow bottle, and contains some methanol, so is NOT approved in aircraft.

I ran this up the flag pole with the Fairbanks FSDO once, since Prist is expensive and a pain in the arse to meter properly, and hard to get. The FSDO guys said I should use "scientific IsoPropyl", so, I got in touch with one of the scientific supply houses, and asked them what percent their "pure" IsoPropyl was.....96 %.

So, I went back to the FSDO with the MSDS for both "scientific IsoPropyl" and for ISO-HEET. They sent copies to OKC, and the response came back from legal that it would appear that the HEET product meets the requirements of the rule.

And, it comes in handy little sealed bottles....perfect for metering into aircraft fuel systems.

Just never, EVER use half a bottle, then save the rest of the bottle for use a week later......IsoPropyl is VERY hygroscopic, and it'll absorb moisture from the atmosphere, kind of defeating the purpose of putting it in your tanks.....

MTV

I think Walgreens sells 99% iso alcohol for about 99 cents a pint.

Don't get the "rubbing alcohol," it's 70% iso or ethyl alcohol.

Gump

VAPOR LOCK . I thought that only occurred on the suction side of a fuel pump on a hot day. Like in a 48 Ford going up the Baker grade at 2 in the afternoon in August.

Baker is the home of the wolds tallest thermometer. http://www.roadsideamerica.com/story/2893
Baker is also gateway to Death Valley.

Tim

i had a problem years ago that was very difficult to find, like you I checked this and that and just couldn't find the problem. It seemed like a fuel issue, perhaps a flow issue.
When the plane was first started it ran just fine but about the time I got where there was no possible place to land it would run rough and pop and lose power.
Each time I checked something and thought I had it fixed it came back, it got so that the problem hit sooner and sooner.

What I finally found was not fuel at all it was both mag input shaft seals were leaking just a tiny bit of oil into the body of the mag. After running for a while the oil would get hot and either vaporise or coat the points until the spark would begin to breakdown or begin to crossfire.

A spare set of mags cured my "fuel" issue for good.

Just something to think about.

qmdv wrote:VAPOR LOCK . I thought that only occurred on the suction side of a fuel pump on a hot day...

When I was 12 I got my first vehicle, a 1941 Willys Jeep. It got vapor lock all the time. I solved it by putting a bunch of wooden clothes pins on the fuel line from the pump to the carburetor.

shorton wrote:
A spare set of mags cured my "fuel" issue for good.

Just something to think about.

Mags were in suspect yesterday as well, I have one that runs fairly rough when doing a mag drop (still within limits) and another that will drop in RPM but stay very smooth. So they will be looked at soon!

Something I wanted to share back to icing theory, It was brought up here about the carb heat possibly not working to the maximum effectiveness. Well looking at my airbox yesterday that was apparent. the shaft that the gate is on has worn part of the box away, no idea where the bushing went. and because the carbheat shaft is crooked in the race, the gate allows some forced air to get by. there is also a hole in the side that i'm sure isn't helping heat air. Also the hole on the bottom was explained to me as a bypass way of getting air if the main intake gets blocked? But should it be closed on carb heat? because it as well is only half shut. So although I get an RPM drop on runup i'm not sure how much good my carb heat did for me.

So fix the airbox and get some clothespins?