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Carbureted vs. Fuel Injected

colojo

Well Known Member
I'm not a builder but I own an RV-8 with the O-360. I'm curious to know what drives a builder's decision to go with a carbureted engine vs. fuel injected and vice-versa. I tried to search the forums for this but couldn't find anything, so forgive me if this is a duplicate post. Thanks.
 
Gee...this should be in the Never-Ending Debate section of VAF.

I chose fuel injection because:

  • I wanted to move from 1930s tech to 1940s tech.
  • No carb icing problems.
  • The possibility of doing lean-of-peak operation properly.

Most of the airplanes I've flown have been carbureted, one injected. Can't say I noticed any difference in performance but they were all wet rentals so wasn't monitoring fuel burn.

I didn't do Electronic Fuel Injection...a little too high-tech for aircraft engines, in my opinion. So it's just standard mechanical, dumb injection.
 
Ralph, your answer is exactly the kind of response I'm looking for. I'm not trying to debate which is "better." I just know that some builders choose carbureted and others choose fuel injected, and I'm just curious to know what drives those decisions.
 
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Advantages of fuel injection?

In theory...based on things I've read about here on VAF and agree with:

Better odds at getting even CHT temps.

More efficient (smoother running when lean of peak).

Sometimes easier starting.

Pressurized fuel is possibly better at handling a little water in the fuel.

Pressurized fuel system is possibly better at handling/mitigating vapor (vapor lock) issues.

Ability to use a purge valve.

Cons:

Slightly more cost and complexity (the definition of modern, no?)

Bevan
 
Ok, I may be in the minority here, but I picked Carb for my brand new Aerosport 0-360. I also picked fixed pitch, but did go dual p-mags as a nod to modern technology.

As to why the Carb,

I wanted the easy to start of a carb
Accelerator pump while cranking and it's off and going.
Didn't want the high pressure fuel pump in the cabin.
Simple setup and troubleshooting
No hot start issues
known operational issues, since I had a carb on my 9A and it worked just fine.
I really didn't feel like the injected technology was that sophisticated to justify the increased price.
I was not going for inverted fuel & oil during build so that was not a consideration.
 
I went the carb route for:
simplicity
cost
ease of starting when hot (and or high and hot)

I live in the southwest where carb ice is usually not a problem (Lycs not
carb ice prone anyway).

I have a one electronic ignition and one mag. Although not as efficient as
a fuel injected system, I can still save approx 10% in 65% cruise or less.

All of my reasons can be debated. But I'm happy with my choices.
 
There must be some reason bush pilots choose carbs. After all, not being able to start your plane in the bush could be a life or death issue.

If you go with a carb, you can always sell it later as ns install injection.
 
- No icing issues (like carb- had this happen, scary)
- More even (tunable too) fuel distribution to each cylinder, better cyl/cyl A/F balance
- Extend the lean limit as all cylinders are closer together
- Possible negative G operation (bonus: not for me . . . yet)
- FI allowed forward facing servo and more compact under cowl (bonus)

Negatives are complexity and cost.
 
There must be some reason bush pilots choose carbs. After all, not being able to start your plane in the bush could be a life or death issue.

If you go with a carb, you can always sell it later as ns install injection.

I was a bush pilot for 4 years. Everything I flew (except turboprops) was injected.

It does take practice, though.
 
Ok, I may be in the minority here, but I picked Carb for my brand new Aerosport 0-360. I also picked fixed pitch, but did go dual p-mags as a nod to modern technology.

As to why the Carb,

I wanted the easy to start of a carb
Accelerator pump while cranking and it's off and going.
Didn't want the high pressure fuel pump in the cabin.
Simple setup and troubleshooting
No hot start issues
known operational issues, since I had a carb on my 9A and it worked just fine.
I really didn't feel like the injected technology was that sophisticated to justify the increased price.
I was not going for inverted fuel & oil during build so that was not a consideration.

Exactly the reasons I went with a carbed engine 16+ years ago for the RV-6. I have never seen any reason to change to fuel injection in the years since.

Different mission profile might call for fuel injection, but for my plane the carb is the best fit.
 
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I think it has been summed up already.

Carb:
- cheaper
- easier hot start
- more simple both to install, use and replace

FI:
- able to adjust amount of fuel to each cylinder for tuning, thus...
- can fly LOP much more effectively and efficiently
- most small spam cans don't have this option, but we do because we're experimental.
 
I like carb for the same reasons I like Lycomings.
They are cheaper, simpler, usually easier starting, require less fuel pressure, etc.

When I built my -6 back in the early '90s, I looked into fuel injection. If you do sustained inverted flight, injection has a real advantage. Other than that I consider the advantages small.

BTW, my carb set-up allows for VERY close EGT readings.

These are experimental aircraft, do what makes you happy!
 
The IO's are also a little less cluttered under the cowling--no tubing/mechanism/cable for carb heat, often no gascolator.

I went injected primarily because my trainer had injection...more of a familiarity thing.
 
Easier to start???

I tried to stay out of this, but after post after post saying that carbs were easier to start (meaning fuel injection is difficult to start) I had to speak up. Starting a hot fuel injected Lycoming is a brain dead job. If you are having problems, then it is a pilot technique problem.

Here is all you have to do:
You shutdown your engine by moving the mixture to cutoff. Ignition off, master off.

Your start your hot engine by doing NOTHING!
1) Leave everything where it is.
2) Just crack the throttle (just like a carb)
3) Turn on the master and the ignition.
4) Engage the starter.
5) When the engine starts move the mixture to rich

I don't care what your instructor taught you. Do nothing but ignition on, and hit the starter. If you turn on the boost pump, and/or prime it, and it won't start, that's your incorrect pilot technique, not fuel injection.
 
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I tried to stay out of this, but after post after post saying that carbs were easier to start (meaning fuel injection is difficult to start) I had to speak up. Starting a hot fuel injected Lycoming is a brain dead job. If you are having problems, then it is a pilot technique problem.

Here is all you have to do:
You shutdown your engine by moving the mixture to cutoff. Ignition off, master off.

Your start your hot engine by doing NOTHING!
1) Leave everything where it is.
2) Just crack the throttle (just like a carb)
3) Turn on the master and the ignition.
4) Engage the starter.
5) When the engine starts move the mixture to rich

I don't care what your instructor taught you. Do nothing but ignition on, and hit the starter. If you turn on the boost pump, and/or prime it, and it won't start, that's your incorrect pilot technique, not fuel injection.

That's how I was taught, too, albeit with a Continental (Diamond DA-20). Hot starts were never an issue.
 
Injected hot starts a no brainer, however I see students from Miami at my field burning up starters trying to hot start carbed engines at least twice a week.
 
What Danny Said

Danny is correct. He knows. I agree. Get a FI engine when building your RV8, 7,14,10,,, all of them.

I have carberators on my airplanes. RV8 'Borrowed Horse' has an O-360 A1A, 'Shooter' my EXP Super Cub has O-360 A4M,,,carb,, my 1976 Cessna 180J 'Paul Reveer' has a carb on its O-470S engine. All three work fine.
I had a P35 1963 Bonanza for 5 years operating in the tropics, eastern Caribbean. Read hot! Never had trouble starting that IO-470, using Danny's
Method.
 
If you do sustained inverted flight, injection has a real advantage. Other than that I consider the advantages small.

Agree with this statement if you take the word "sustained" out of it. A carbureted engine will quit very quickly when inverted. It will resume operation very easily once upright. If your aerobatics don't include negative "G" flight a carburetor may be your choice. For me, negative "G" flight is what I do and I also appreciate the fuel savings that lean of peak operation provides with fuel injection.
 
I've flown various I/O-320/360/470/520 (and most of them in bush planes). If your cruising around ROP, it really does not matter, carb or FI. Each cylinder is getting a little too much fuel, makes power and airplane goes forward. Sure, some cylinders might be 50d apart in CHT, but the engine doesn't seem to care.

I don't have an engine yet, but I'm going to go injected because of the ability to go up-side-down for longer. The ability to go LOP will also pay for the increased cost of the fuel injection.

As far as starting, just talk to other pilots with similar setups. There's various tricks out there that will start just about every engine, hot or cold. If it won't start, it means your doing it wrong. (My boss has a trick for the IO-520 series that's so dead simple, a brain dead monkey could start it. Hot or cold, doesn't matter).
 
Go back to carb?

I know of no one, including myself, who would want to go back to carbs after experiencing Injected. It is just flat superior and as someone pointed out, it's free because of fuel savings. YMMV

Anyone want to return to a carb?

Jerry
 
I know of no one, including myself, who would want to go back to carbs after experiencing Injected. It is just flat superior and as someone pointed out, it's free because of fuel savings. YMMV

Anyone want to return to a carb?

Jerry

I certainly would not hesitate to recommend fuel injection to a builder.

However, the carb on my 16 year-old RV-6 works.....very nicely.

Yes, it is 'ancient' technology, often disparaged for its mechanical crudeness, but it works.....very nicely.

I don't fly often or high enough to ever see fuel savings that would pay for FI. (I paid $3.35 for 93 no-ethanol car gas this morning!) I suspect there are many other RVers in similar circumstances. I won't be returning to a carb, but I will be keeping one. :)
 
I don't fly often or high enough to ever see fuel savings that would pay for FI. (I paid $3.35 for 93 no-ethanol car gas this morning!) I suspect there are many other RVers in similar circumstances. I won't be returning to a carb, but I will be keeping one. :)

Sam,

Are you saying that you don't run lean of peak at low altitude? If not, why not?
You can run lean of peak at any altitude!
 
Sam,

Are you saying that you don't run lean of peak at low altitude? If not, why not?
You can run lean of peak at any altitude!

Very difficult (impossible?) to run lean of peak at any altitude with a carb due to uneven fuel distribution. I lean according to engine roughness and looking at the single EGT probe on #3 cylinder and fuel flow (and familiarity with my engine over the past 1400 hrs). Same way we learned to lean in the C172. :)

As I stated, mine is a simple setup but ideal for my flying. I average less than eight gallons/hr and it never fails to start on the 2-3 blade.
 
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Very difficult (impossible?) to run lean of peak at any altitude with a carb due to uneven fuel distribution. I lean according to engine roughness and looking at the single EGT probe on #3 cylinder and fuel flow (and familiarity with my engine over the past 1400 hrs). Same way we learned to lean in the C172. :)

As I stated, mine is a simple setup but ideal for my flying. I average less than eight gallons/hr and it never fails to start on the 2-3 blade.

Perhaps my EFII ignition helps, but I can run LOP with my O-360 quite easily. Above 60% power I tend to set my throttle more towards evening the EGT's within 20-30* and pulling the mixture to LOP which yields 152-155 knts true an 7ish GPH around 6500 MSL. I can run higher power settings LOP, but pushing the throttle in increases my EGT spread and smooth LOP operations are very finicky. I'm sure FI would be better but not worth changing it out for me at this time.

Just saw you had a single EGT, I would also lean like a 172. A 4 cylinder engine monitor is awesome!
 
Perhaps my EFII ignition helps, but I can run LOP with my O-360 quite easily. Above 60% power I tend to set my throttle more towards evening the EGT's within 20-30* and pulling the mixture to LOP which yields 152-155 knts true an 7ish GPH around 6500 MSL. I can run higher power settings LOP, but pushing the throttle in increases my EGT spread and smooth LOP operations are very finicky. I'm sure FI would be better but not worth changing it out for me at this time.

Just saw you had a single EGT, I would also lean like a 172. A 4 cylinder engine monitor is awesome!

Those are the same numbers I'm seeing with my O-360. I believe it is the dual P-mags that let me run over 50 degrees LOP.
 
I tried to stay out of this, but after post after post saying that carbs were easier to start (meaning fuel injection is difficult to start) I had to speak up. Starting a hot fuel injected Lycoming is a brain dead job. If you are having problems, then it is a pilot technique problem.

Here is all you have to do:
You shutdown your engine by moving the mixture to cutoff. Ignition off, master off.

Your start your hot engine by doing NOTHING!
1) Leave everything where it is.
2) Just crack the throttle (just like a carb)
3) Turn on the master and the ignition.
4) Engage the starter.
5) When the engine starts move the mixture to rich

I don't care what your instructor taught you. Do nothing but ignition on, and hit the starter. If you turn on the boost pump, and/or prime it, and it won't start, that's your incorrect pilot technique, not fuel injection.

While I agree that Injection Hot Starts are pretty easy, my IO-360-M1B won't respond to the above. I always have to give it a short shot with the boost pump, presumably to fill up the previously boiled out fuel spider lines. Maybe a difference between the angle valve and parallel?????

In regards to Inj vs Carb. You'll have to pull the injection system from my cold dead fingers. I ain't givin' it up. :)
 
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Mogas

One more reason to go fuel injected!
If you have your mind on eventually using mogas, you'll be far better off with a fuel injected system.

1: Fuel injected systems are available and approved for use with all types of fuel including ethanol.
2: High pressure fuel lines significantly reduce vapor lock occurrence.
 
carb vs injection

Possibly with the new avfuel coming out a injected engine may have limitations... I know with a carb you can burn ethanol free gas which you would never want to do with injection because of potential vapor lock issues.
 
What????

Possibly with the new avfuel coming out a injected engine may have limitations... I know with a carb you can burn ethanol free gas which you would never want to do with injection because of potential vapor lock issues.

I have been burning ethanol free premium Mogas for over 1000 hours! Where do you get your information?
 
Possibly with the new avfuel coming out a injected engine may have limitations... I know with a carb you can burn ethanol free gas which you would never want to do with injection because of potential vapor lock issues.

There is no way a new FAA-accepted fuel will cause problems to a big chunk of aircraft engines.
 
Possibly with the new avfuel coming out a injected engine may have limitations... I know with a carb you can burn ethanol free gas which you would never want to do with injection because of potential vapor lock issues.

Not only can burn ethanol free gas but especially mogas with ethanol when using fuel injection.
AFP's fuel injection is approved for all types of fuel including ethanol.
High pressure fuel lines go a long way in helping prevent vapor lock.
Dealing with any and all aspects of burning mogas, ethanol or not, are far better using fuel injection vs. a carby.
 
That's why I went with AFP fuel injection and automotive electric fuel pumps w/ turndown regulator. The regulator maintains fuel pressure by returning excess fuel to the selected fuel tank.
As far as I know, Lycoming and the aftermarket suppliers have not blessed the use of ethanol blended fuel in their mechanical fuel pumps.
I don't really intend to use ethanol blended fuel, as Washington State still has ethanol free fuel available at a few stations, but I just like the idea of being able to use the widest variety of fuel.
 
As far as I know, Lycoming and the aftermarket suppliers have not blessed the use of ethanol blended fuel in their mechanical fuel pumps.

I posed the question to Lycoming several years ago "Do the materials in your fuel pumps tolerate ethanol?". They declined to answer, citing "trade secrecy". I asked the same question to Tempest engineers about the Lycoming pumps that they rebuild with certified parts. They told me that their pumps ARE ethanol tolerant. BTW, the Vanguard Team flies on 100% ethanol with Lycoming fuel pumps and has been doing it for years.

I have used 10% ethanol in my RV with no apparent damage to my stock Lycoming fuel pump. Because I have a ready supply of non-ethanol premium mogas available I no longer wish to use an ethanol blend.
 
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I tried to stay out of this, but after post after post saying that carbs were easier to start (meaning fuel injection is difficult to start) I had to speak up. Starting a hot fuel injected Lycoming is a brain dead job. If you are having problems, then it is a pilot technique problem.

Here is all you have to do:
You shutdown your engine by moving the mixture to cutoff. Ignition off, master off.

Your start your hot engine by doing NOTHING!
1) Leave everything where it is.
2) Just crack the throttle (just like a carb)
3) Turn on the master and the ignition.
4) Engage the starter.
5) When the engine starts move the mixture to rich

I don't care what your instructor taught you. Do nothing but ignition on, and hit the starter. If you turn on the boost pump, and/or prime it, and it won't start, that's your incorrect pilot technique, not fuel injection.

This is a very strongly worded post, and I must mention that in my experience this technique does not work in all airplanes with FI. In mine, this technique will cause the engine to immediately fire when hot, but dies one second later. You cannot get the mixture in fast enough. Does not work for me. YMMV.
 
This is a very strongly worded post, and I must mention that in my experience this technique does not work in all airplanes with FI. In mine, this technique will cause the engine to immediately fire when hot, but dies one second later. You cannot get the mixture in fast enough. Does not work for me. YMMV.

Neither works for me, not repeatable at least.

My technic is to give a very short boost pump (1-2 seconds) with both throttle and mixture fully aft. Then I will push the throttle fully in but leave the mixture at cutoff. While cranking, pull the throttle back slowly till the engine starts at which point I will push in the mixture knob slowly in.

This is the most repeatable procedure for my engine.
 
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