Carb ice, or more?

[Clip4]

Ah. Such a reliable source.

Their "view." That comes from a lack of experience and knowledge, not from any factual risks. Those same mechanics will blithely replace an engine, reconnect all the controls, fuel and oil lines, a far more complex job than opening a mag for inspection.

Slicks are easier to work on than Bendixes.

I suppose all this is your point of view and may be true, but last time I checked the people who operate the business determine the risk/reward not the customer.

Here is what an updated 2019 article in Aviation Consumer says.

IRAN v. Overhaul​

When your Bendix mags hit 500 hours in service, we recommend yanking them and sending them out to a specialized magneto shop for IRAN. For Slicks, we suggest getting an estimate for IRAN versus checking prices for rebuilt units—as they may be comparable and it can be faster to simply get rebuilt mags.

We do not recommend overhauling a magneto. To tag a magneto as overhauled, a shop must replace all of a specific list of parts, even if they are perfectly serviceable. Our research into prices showed it was generally twice as expensive to overhaul a mag as to inspect and repair and replace parts as needed. Depending on the parts that have to be replaced, we figure on $500-$700 for IRAN of a big Bendix mag—the smaller mags are less expensive. Bendix mags can be IRANed indefinitely. They do not need to be overhauled.

 

[Magman]

Mags are all the same; only different!

Anyone considering servicing mags would have little trouble with the

principles while switching from one brand to another.

However; that’s where it ends. There is very little interchange between

brands. Parts, tools, lubricants and techniques differ between them.

Even the screwdrivers and pullers won’t work on the other brand.


My take is this is a big factor in determining whether a shop will

work on mags, Buying tools, stocking parts and staff capability

training can be prohibitive if there is only a small volume of mags.

Shops such as Aircraft Magneto Service charge about $300 plus parts

fora 500 hour. I’ve never talked to anyone that was not happy with them.

 

[Dan Thomas]

We do not recommend overhauling a magneto. To tag a magneto as overhauled, a shop must replace all of a specific list of parts, even if they are perfectly serviceable.

And I don't, either. Definitions matter. From the "Interpretation" section of our Canadian Aviation Regulations, we see this:



And this:



A magneto inspection is an inspection, with replacement of defective parts such as points or condenser or distributor block or rotor. An overhaul returns a component to a status that makes it good for another engine life, i.e. 2000 hours. It requires more work, training and equipment than any inspection and adjustment. Just about everything other than the case and rotor gets replaced. It requires a test stand that drives the magneto to a certain RPM and measures spark distances. It becomes (in Canada, at least) Specialized Maintenance, limited to those shops and personnel that are certified to take it to that level. In the US, I don't think so. From the CARs:



This is the Slick magneto overhaul manual's list of parts that must be discarded and replaced with NEW (no recycled or salvaged parts) at mag overhaul:


Like I said, everything except the case, rotor and rotor drive gear. The "rotor gear" above is the plastic gear that drives the distributor rotor.

This is a magneto test stand, required for magneto overhauls. How often have you seen one in a GA maintenance shop?



For a lot of magnetos, the parts and labor cost for an overhaul can be much more than the cost of a new mag.

Once again, a 500-hour mag inspection IS NOT AN OVERHAUL. The magneto manuals make stark distinctions between them. They have the requirements for 100 and 500 hour inspections, and a whole separate section dealing with overhauls.

Anyone sending their mags out for expensive overhauls at 500-hour intervals does not understand the difference. They are wasting a lot of money for no good reason.

 

[Mikey52]

The guy that does our 500 inspections, uses that machine to test our mags before going out the door.

 

[Dan Thomas]

The guy that does our 500 inspections, uses that machine to test our mags before going out the door.

That's good, but not required by the Slick manual, and probably not by Bendix either. If the coil, points and condenser are good, and the E-gap properly set, the spark will be hot and the engine will start easily and have low mag drops on runup.

But if the guy has the machine, why not use it? Doesn't take long.

 

[tzink]

Hi everyone, new to the forum, arrived here on a search for carb ice in a 150.
I wanted to revive this thread because I am experiencing the same problem in my Cessna 150L. I flew about 60 hours in it since i bought it, problem free. Then on a cross-country in cruise, I experience identical burble and roughness as OP. I rammed the mixture forward and it resolved. Only to come back later in the day on the next leg. This time mixture in made it worse. Carb heat made it better.

I have experienced the same problem intermittently since. Most recently yesterday. OAT was 10C, with no visible moisture and a 25C dewpoint spread. So, not impossible for ice but definitely not in the high risk zone. Intake temp was around 34-44F with carb heat off. Cruising with carb heat on, I was only getting 60F on the intake temp. After flying with carb heat on for about an hour, I turned it off to see how things were doing. When I turned carb heat off, the engine ran noticeable worse, with a significant vibration. Played with mixture, but couldn't get it to resolve. I landed. Did some pattern work after, and all was normal.

Even on 100F+ days my intake temp sits no higher than 50F with carb heat off.

To avoid the whole magneto overhaul distraction from the last several posts, I have 300 hours since mag overhaul, new spark plugs, and new mag harness. Plane just came out of annual 7 hours ago.

I have flown with my regular mechanic but of course I can't get it to replicate the problem with him on board.

Definitely makes me nervous to go fly. Less confidence in the machine.

Other thoughts welcome!

 

[Gary Ward]

Hi everyone, new to the forum, arrived here on a search for carb ice in a 150.
I wanted to revive this thread because I am experiencing the same problem in my Cessna 150L. I flew about 60 hours in it since i bought it, problem free. Then on a cross-country in cruise, I experience identical burble and roughness as OP. I rammed the mixture forward and it resolved. Only to come back later in the day on the next leg. This time mixture in made it worse. Carb heat made it better.

I have experienced the same problem intermittently since. Most recently yesterday. OAT was 10C, with no visible moisture and a 25C dewpoint spread. So, not impossible for ice but definitely not in the high risk zone. Intake temp was around 34-44F with carb heat off. Cruising with carb heat on, I was only getting 60F on the intake temp. After flying with carb heat on for about an hour, I turned it off to see how things were doing. When I turned carb heat off, the engine ran noticeable worse, with a significant vibration. Played with mixture, but couldn't get it to resolve. I landed. Did some pattern work after, and all was normal.

Even on 100F+ days my intake temp sits no higher than 50F with carb heat off.

To avoid the whole magneto overhaul distraction from the last several posts, I have 300 hours since mag overhaul, new spark plugs, and new mag harness. Plane just came out of annual 7 hours ago.

I have flown with my regular mechanic but of course I can't get it to replicate the problem with him on board.

Definitely makes me nervous to go fly. Less confidence in the machine.

Other thoughts welcome!

Use carb heat often and trust your aircraft is my suggestion.
I run a power flow exhaust which contributes greatly to carb ice. I experience it almost every flight all year long especially descending if I don't use carb heat.
But I have it had climbing out and during cruise out of the blue all year round. I fly a lot some weeks every day.
I use carb heat a lot and then I don't experience it. Been flying my combo since 2018 and just about know when ice is possible, so use carb heat often on every flight.
On my 172...
I believe the tuned exhaust speeds up the intake charge increasing the air thru carb and the intake runners even at idle and the collector in the the exhaust is smaller then the stock muffler so the there is less ambient heat on the outside of the carb to keep ice at bay.
I get carb ice soon after I start it sitting on the ground if I let idle a little high like 1100-1200 rpm many days year round. When the engine is cold carb heat don't help much until the engine gets 2-3 minutes of heat then it stops carb ice within 5 seconds or less. So I know it is carb ice. If I blend in some warm air on the ground then it does not do it. Same with climb out on days when the conditions are right I blend in a little hot air on the climb out and it won't do it. So I know it is carb ice. I am used to it.
I have it do it in cruise shortly after I take off sometimes, then it might take 10 seconds to melt, but it always melts and then runs great. But those approx 10 seconds in the air is a long time waiting for the ice to melt, but I am used to it now.

Like said descending will make carb ice every time especially through clouds. My wife used to freak out when the engine gets rough now she just mumbles "carb heat please!" if I let it happen when she's in the plane.

 

[Magman]

Mags usually fail in flight but it’s not apparent until the next mag check.

Coil failures are often heat related.

2 days ago I replaced a mag that had a new(;?) coil fail after 30 hrs.

I’ve seen several that are fine cold; fail when hot and “heal” when cold!

 

[tzink]

Mags usually fail in flight but it’s not apparent until the next mag check.

Coil failures are often heat related.

2 days ago I replaced a mag that had a new(;?) coil fail after 30 hrs.

I’ve seen several that are fine cold; fail when hot and “heal” when cold!

I flew yesterday, just circling the field at 4500' so I could futz with things. Did several mag checks in flight, all normal results.
I did find that the higher I went, the more engine vibration I got. I also flew in prime carb ice conditions for an hour with no carb heat, and got no indication of ice. Turned carb heat on, and got no ice melt burble.
So I'm starting to think my problems might be related to the fuel air mixture and the carb itself rather than ice.

 

[Dan Thomas]

So I'm starting to think my problems might be related to the fuel air mixture and the carb itself rather than ice.

There is this Airworthiness Directive that you should study: https://drs.faa.gov/browse/excelExternalWindow/9F87A5E42C10900C86256A410065C0CD.0001

An excerpt from it:

This amendment is prompted by service difficulty reports describing engines that fail to attain rated power, run rough, or experience power loss after installation of a one-piece venturi in accordance with the existing AD, and by incidents of forced landings of aircraft powered by engines modified to comply with the existing AD.

This AD was issued three times, amended each time. The initial issue was the two-piece venturi that would work loose and the secondary part of it could get sucked into the engine. Even if it didn't get that far, that secondary was the one that generated most of the suction that drove the fuel flow from the main nozzle, and the engine would quit.

The new one-piece venturis were horrible, They had support legs for the secondary, and those legs had flat bottoms that caused turbulence and messed up the airflow and fuel atomization and homogeneity. So the AD was amended to require a nozzle with cross-drillings to improve the atomization. For some engines, that made things worse, so a third amendment allowed you to install the old two-piece venturi and undrilled nozzle, and inspect the venturi every 100 hours for looseness. But most of those parts had been trashed. So now we have a whole fleet of those carburetors that are much worse than the old Bendix/Strombergs from the 1940s. Horrible things.

There is one more potential problem with your carb. The O-200's carb is unique in that its intake manifold is mounted so that it can rock a little on its studs. This particular carb on this particular engine gets shaken pretty hard, sideways, every time a cylinder fires, and it sloshes fuel out of the float bowl vent into the space behind the venturi, where the air is dead and therefore is at static pressure, and that fuel gets sucked into some cylinders and makes them run rough. Way too many mechanics pay no attention to the engine manuals, and get the mounting all wrong. Go to this thread and read my post:

https://www.pilotsofamerica.com/community/threads/0-200-rpm-loss-on-take-off.137511/#post-3238329

 

[sansoneservices]

It does sound like Carb Ice to me ; BUT!

Even a blind squirrel finds a nut a times.

Sometimes you have fix something and then find is was the issue.

How are the muffler baffles ?

I‘ve talked to folks that had them failing and CH would “ fix”.

So would changing frequencies, adjusting trim etc.

The Carb Heat system on 150s is often hooked up wrong.

The vertical “ Scoop” on right forward side of engine is for CABIN Heat.

The inlet for CH has a horizontal port that is “ sheltered” by the

lip of the nose bowl. The baffle with the port is very convenient for

placing screws during cowl removal. They DO fall in there and live in

the duct below. The duct below make a U bend to attach to the muffler.

The screws may be found at the bottom of the U bend. Water, critter

material are also easy to get in the system this way. Water is trapped

at the bottom and causes the wire in the duct to rust away and ruin

the duct. Poking a small hole there will allow water to drain. You want

this area kept free of anything that can get to the Carb.


There are 4 sumps in the fuel system of a 150. Often missed is the one on

the belly below the Fuel Shut - off. Some have had a quick- drain added

but most retain the stock cap and lock plate. i always check at inspections

and usually find water and crud there.


Lots of other tests including mags, carb etc but best to start with easy stuff.

My fuel selector had a 1/8 npt plug and water collected there. I added a quick drain BUT you must ensure the drain doesn't interfere with selector valve rotation.

 

[Magman]

The AD Dan referred to also SB MSA2.

A stamped “V” identifies the one-piece.

It can mimic LEAN operation but sooty plugs, pipes and fuel consumption

is like a very RICH Mixture.

It’s also possible that you still have the original 2 piece Venturi which

can cause similar symptoms. It must be checked for security by dropping

the Carb or Airbox.

Improper atomization/vaporization can result from previous problems.

Incomplete combustion results from this issue. Plugs, pipes and fuel burn

may provide clues.