Carburetor Icing 0-540?

[Berniepiet]

I am new to the O-540. Flown mostly continentals all my life. Is the O-540 prone to carb icing? Has anyone in this group ever gotten carb icing in an 0-540? Thanks

[Mark Goldberg]

Hello Bernie. In my time flying an O540 I got carb ice once. Noticed it and got rid of it fast. My understanding is that Continentals ice up much more often than Lycs. Mark

[Battson]

I would have assumed this had everything to do with the throttle body you install, you have a range of choices. The throttle assembly is sized to suit the engine - but overall the engine doesn't dictate a fixed carb (with fixed icing characteristics).

If you are worried, go for fuel injection. It's fantastic for increased power, economy / efficiency, and very popular in the Bearhawk community.

[rv8bldr]

Hey Bernie

I have a O-540-J in my Maule and it is terrible for carb icing at anything less than full throttle. I don't know if it is systemic with this engine in Maules or if I am just "lucky" :-) Regardless, I decided to modify the O-540-A that I bought and overhauled for the Bearhawk to have a Bendix fuel injection system (that I bought used off of the Vans Forums). I had the same injection unit on the IO-360-A3B6D in my RV-8 for years and loved it.

YMMV, Batteries not included, Objects in mirror are closer than they appear, etc.

[rodsmith]

That's really interesting. I flew a Maule with the same engine in Alaska for over 500 hours. Believe the only time I ever pulled carb heat on was to check it before takeoff. Wonder why such different experiences?

[rv8bldr]

Hey Rod.

I have no idea. It makes no sense. Maybe the air is moister here in flying season (Eastern Ontario?) However, it has happened enough times that I know it isn't my imagination. If I am just tooling around at 20/20 turning dinosaurs into engine noise, I periodically put carb heat on as a preventative measure now. If I am going somewhere, I am in the "oversquare" club with WOT and about 2000 RPM. At 6500' that yields about 125 kts TAS and 11.2 GPH. I have the three blade McCauley prop.

[robcaldwell]

I have a quote from Bob for a carbureted engine (O-540). The quote indicates a carb temperature probe.

But I'm with Battson... Fuel injection is the way to go. Hot starting is my only complaint there.

[zkelley2]

I've never seen carb ice in a lycoming. I have a carb temp sensor and only in the winter does it reach a temp that ice could even form. When it's too cold to have any water in the air. This is because the carb is heated by the oil pan it's bolted to. There might be a lycoming configuration that's not true, but I don't know of one.

Continentals on the other hand require you to carry tequila and a blender for all the ice the make.

Injection is nice, but if you already own the carb, you won't make the fuel savings back over injection before the 2000 hour overhaul so just run it.

[Berniepiet]

Thanks for all the input. Appreciate it

[Battson]

Injection is nice, but if you already own the carb, you won't make the fuel savings back over injection before the 2000 hour overhaul so just run it.

Err em, are you kidding?

Most people with injection are saving up to $75 (NZD) per hour with these fuel prices these days, by running LOP due to having fuel injection. Something that almost all carb engines will not do. To continue the example given, over 2,000 hrs flying that is more than enough to pay for a brand new engine (with injection fitted).

[zkelley2]

Injection takes the mogas possibilities away. Raising the fuel cost about $2us a gallon here. Also, my hourly total fuel cost is only about $90NZD. I can't possibly save $75/hr.

[Battson]

We can discuss the details, but it easily pays for itself either way.
They can't keep fuel prices artificially low forever, so it's only getting cheaper
I was told by my engine manufacturer that I could still run mogas with injection, but over here there's really no need.

[zkelley2]

I was going to swap the carb for injection when I was building. I ended up not doing that because it would cost more in fuel over the life of the engine.

You can't get the mogas STC on any injected lycoming. The issue is the mechanical fuel pump gets quite warm are you can in theory have boiling fuel at the inlet. The inline boost pump should take care of that, but it's not ideal IMO. Not that we need an STC, but I'd not personally run mogas through a mechnical pump. EFII, sure. Honestly for the price of getting bendix injection, I'd go full EFI instead.

100LL is $7.63 here right now.
Premium ethanol free mogas is $4.99

I burn 11gph in cruise, let's assume the typical injection and LOP ops reduces fuel burn by 1gph.

$54.89/hr for mogas. $76.30/hr for low lead burning 1gph less. After 2000 hours the fuel injection will have cost me $42,820 more. Or more than the overhaul.

Low lead will never be cheaper than mogas, even the new gami stuff is supposed to be about the same price.

And I also have a need to run mogas that isn't just cost. 2-3 times a year I end up in a village in need of fuel and they don't sell anything but 87(r+m/2) at the car pump you have to taxi through town to get. That's been a lifesaver. Which is also why I have the SDS CPI, so I can run a timing map that 87 is safe on when necessary.

[Battson]

I burn 11gph in cruise, let's assume the typical injection and LOP ops reduces fuel burn by 1gph.

That's interesting. We would normally burn around 55 L/hr ROP but that can be anywhere from 28 to 42 L/hr LOP, so the savings potential is enormous with LOP.

Almost nobody is burning mogas here, it's practically never available at airports and the savings are much smaller than in your example - maybe 20 or 25% depending on where you live.
It would be better if you somehow claim back the road tax (which is a huge PITA and practically not worth the effort for most).

So in NZ it's a lot more attractive to use fuel injection and run lean of peak, sounds like that's not the case in some parts of the USA.

[zkelley2]

I should have also specified airspeeds. The 11gph(42LPH) is at 113 KTAS. 113 is the sweet spot for my airplane, where I can go faster, but you're burning more and more fuel to do it and it's not worth it. 14GPH nets me 120kts. These are all properly leaned with the carb. 3gph for 7kts is not worth it.
I don't get down into 9gph until I'm back around 85kts or so, but I've never actually tried to cruise long distance at that speed so, I'm probably not properly leaned there. 2gph for 23kts is worth it.

For folks reading that and thinking slow, I'm on 31s and those cost me 15kts for the same fuel burn when I switched.

We don't have mogas at any airport I'm aware of. We all have fuel tanks in a trailer or truck that we fill up at the station. Honestly it saves a good bit of time not having to wait in line at the self serve at the airport on a nice day. And ya, it'd be nice if I could get the road tax back, but they don't do that. That's $0.26 a gallon. Avgas has a tax on it for the air infrastructure - $0.23/gal so it's mostly a wash.

[Bcone1381]

55L = 14g
28L = 7.4g
42L = 11.1g

[rv8bldr]

It is certainly worth it here in Canada, in my opinion. Premium auto fuel (without Ethanol) here in my part of Ontario is around $1.90 - $2.00 / litre. It is virtually impossible to get it at any airport. (BTW, $2.00/l = $7.57/gal)

Avgas is anywhere from $2.70 - $3.00 / litre, and a lot more in the remote areas.

This is one of the reasons I bought a used FI system from an IO-540 in an RV-10 to retro fit to my carbureted O-540-A.

[zkelley2]

$1/L would more than make up for the inefficiency of a carb. There's a bigger difference between you're premium and avgas than there is mine. But ya, you have to get the mogas to the airport. Some of the guys that live on airstrips will have 500+ gallon tanks and get the fuel delivered.

[schu]

Around here non-eth mogas is a premium product, so it's usually only $1.50/gal cheaper than avgas at the airport, but when I buy the avgas off airport they are usually within $0.25 of each other. Once mogas and avgas are both purchased off airport and at a similar price point, then having injection really starts to make sense. As for the issues:

1. I changed my fuel system so that I have a tee just past the mechanical pump that has a small 1/8" line back to the tank to that I'll put a restrictor in to bleed 7-8gph back to the tank to keep the pump cool and to give vapor a place to go. I'm not flying yet, so I don't know if it will work, but it probably will and would allow me to safely run mogas with lycoming injection. If it doesn't work, I'll cap off the tee and press on.

2. Hot restart issues can be partially resolved with electric ignition which will ignite fuel mixtures a mag wouldn't touch. Electric ignition also gives you a little more timing when LOP which is useful to get a few kts back because super lean mixtures burn slower.

We'll see how it all works out when I'm flying. I starting on fabric now.

[Battson]

Hot start issues... I've never heard of any consistent hot start issues with a FI Bearhawk. I've seen our crew here do literally hundreds of hot starts, and have done maybe a thousand myself, if anything they are easier than cold start. They practically never fail.

[Nev]

For folks reading that and thinking slow, I'm on 31s and those cost me 15kts for the same fuel burn when I switched.

Can I ask, what tires did you switch from ? I'm about to install ABW 29's.

Another data point for the discussion:

ROP I burn 55 LPH (16 GPH) at 120 KIAS.
LOP I burn 38 LPH (10 GPH) at 115 KIAS.

[schu]

Zach will probably comment soon, but I'm 95% he was on 8.50's

[Bcone1381]

.......
1. I changed my fuel system so that I have a tee just past the mechanical pump that has a small 1/8" line back to the tank to that I'll put a restrictor in to bleed 7-8gph back to the tank to keep the pump cool and to give vapor a place to go. I'm not flying yet, so I don't know if it will work, but it probably will and would allow me to safely run mogas with lycoming injection. If it doesn't work, I'll cap off the tee and press on.

Have others done this? As discussed above, auto fuel it must be kept cool. I have not heard of bleeding fuel off before. Can I assume that when you bleed off fuel, fuel travels faster through the pump and spends less time being warmed up in the pump? I have installed a cooling shroud on my pump.

[schu]

A fellow with an RV-10 did this and has been running ethanol mogas on an injected lycoming in CA, so that's one datapoint. The other is that having a small bleeder vent after the mechanical pump more or less makes this work like the continental injection, which can run mogas.

All of this said, you must have enough fuel flow to loose 6-8GPH past the pump without the boost pump running, so I need to make sure that I can get 30-35GPH through the boost pump to the inlet of the engine pump (so that it's never sucking) on single tank operation. To do this, I have run 1/2 line from the tank to tee under the door, then 3/8 the rest of the way. Basically all downhill fuel is 1/2 line and uphill fuel is 3/8 line. I suspect I'll have the flow, but if I don't, I'll cap it off and press on.

Honestly, my current situation with purchasing fuel off airport means I'll just run 100LL all of the time, but I wanted to have plan B because who knows what's going to happen 10 years down the road.

[kestrel]

I'm running a carburetor equipped O-540. I've seen ice a few times when temperatures were cool and humidity high. It has never been an issue.