# Carb vs. Fuel Injection

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#### Celt902

##### New Member
I am considering buying or building an Aerolite 103 and am curious what everyone's opinion is of carbs vs. fuel injection. I will be operating from higher elevations in Idaho. My local airport is about 2300' and my house sits around 3050'. I think I am set on the 2-stroke Hirth F-23. I emailed back and forth yesterday with a Hirth dealer and he suggested fuel injection to solve my density altitude issues. Today I was watching some videos for the Hirth F-23 specifically and I hear carbs are better and far more reliable (but it was from 2 years ago). I know almost nothing about these small engines so I was curious what opinions I could gather here. I realize fuel injection is more expensive but if it is safer I am willing to spend it. If not I don't want to waste my money. I weigh about 190 dressed including a helmet.

#### proppastie

##### Well-Known Member
Log Member
It would be best if you can find someone that has used both systems on the engine you are going to buy.....ask the dealer maybe to give you some names, or if there is a user group for the Aerolite ask there....Can you change/adjust the mixture on the fuel injection system?......Certainly you can on the carb....but knowing nothing about 2 stroke engines you had better get some hands on help near by for either system.

#### Armilite

##### Well-Known Member
I am considering buying or building an Aerolite 103 and am curious what everyone's opinion is of carbs vs. fuel injection. I will be operating from higher elevations in Idaho. My local airport is about 2300' and my house sits around 3050'. I think I am set on the 2-stroke Hirth F-23. I emailed back and forth yesterday with a Hirth dealer and he suggested fuel injection to solve my density altitude issues. Today I was watching some videos for the Hirth F-23 specifically and I hear carbs are better and far more reliable (but it was from 2 years ago). I know almost nothing about these small engines so I was curious what opinions I could gather here. I realize fuel injection is more expensive but if it is safer I am willing to spend it. If not I don't want to waste my money. I weigh about 190 dressed including a helmet.
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Do a little Math.

Aerolite 103 with the F33 (28hp) is 235 lbs. Hirth F33 with Electric Start is 45 lbs. 235 lbs - 45 lbs = 195 lbs for Airframe. F23 50hp is 78 lbs + 195 lbs = 273 lbs, including reduction unit, full exhaust, and electric start or 71 lbs + 195 lbs = 266 lbs with recoil start reduction unit and full exhaust, so to make Part 103 254 lbs + 24 lbs = 278 lbs Max with a $4000+ BRS Weight Allowance. While you get 24 lbs Allowance for the BRS, it still Weighs probably 18-20 lbs. A BHP of 50 at sea level and Elevation of 2300 feet is 3.45 HP loss. 50hp - 3.45 = 46.55hp! Aerolite 103 MTOW 600 lbs = 272.1554 kg / 10 kg = 27.21554 kw needed to Fly Well = 36.49664 hp! F33 is 313cc/7cc= 44.7hp is Possible with a Good Tuned Pipe using 11.5cr. With the Hirths 9.5cr - 2hp = 42.7hp. EFI on these Small CC Engines don't make you more hp, but may Improve your GPH use. Hirths EFI SUCKS, You can't Tune it, you have to take it to a Dealer. Mega Squirt or Ecotrons make some nice EFI Setups that You can Tune. IF, you Read both of their Websites you will learn a lot about EFI and LOOK at their Photo's and you can Sorce most of the Parts much Cheaper. Lots of 2000+ Sled Engine have EFI. For Flying out of Higher Elevations, a Turbo with a variable Boost Controller would be nice. Say for Takeoff use 3-4 lbs then reduce it to 1-2 lbs. A Stock 670 was [email protected] 669.2cc/7cc= [email protected] SKIDOO 670 TURBO 11 lbs BOOST at 6750rpm = 163.4hp! 1996 MX Z 670 TURBO 9 lbs of BOOST. [email protected], [email protected] 1996 MX Z 670 TURBO 7 lbs BOOST. [email protected], [email protected] 95hp to 106hp = 11.5789% increase! Weber makes some nice EFI Throttle bodies and so does SFS. The F23 is 78 lbs, including reduction unit, full exhaust, and electric start or 71 lbs with recoil start reduction unit and full exhaust. I believe the Kawasaki 440 is 7 lbs lighter than the Rotax 447UL. The Kawasaki 440 with a Good Tuned Pipe Dynoed making [email protected], [email protected]. Kawasaki 440 is 435.9cc/61hp= 7.145cc to make 1hp. 435.9cc/7cc= 62.2 [email protected] #### Attachments • 29.2 KB Views: 6 #### KeithO ##### Well-Known Member Log Member You might consider the 2 cylinder yamaha phazer engine, it should be good for up to 80hp and much less expensive than the Hirth. 4 stroke, operating at 9000-11000 rpm so would definitely need a reduction gearbox, sold by Skytrax in AZ. The engine comes with all its systems (ignition, injection, ECU etc) as part of the base package. There is some data out there on its flying weight, its basically a Rotax 582 drop in. #### ClaudeR ##### Active Member Hi. I don't have real-world experience, but I would suggest that you also consider the idea that a fuel-injected engine has more things that can go wrong such as an electric fuel pump (which also requires power to run), a control box, etc. If you lose power, the engine won't run (or only as long as there's a battery in the picture to supply power to the pump and electronics). From what I've read, you mostly get better fuel economy and you don't have to worry about proper mixture at different altitudes and throttle settings; the EFI takes care of that for you. Also, my Hirth 3202 with EFI (which is still on a shelf) came with a single fuel pump, so single point of failure. So, I think you have to weigh the benefits of better mixture control against the possibility of less reliability. Just my thoughts. #### Daleandee ##### Well-Known Member I'm a carb kinda guy. Had Bings on my two strokes and now a Marvel Schebler on my four stroke. My Marvel is gravity fed so there's less to fail. Fuel injection has come a long way and it seems to be very reliable but as mentioned there are more things to go wrong i.e. fuel pumps, pressure regulators, ECMs that drive the injection system, wiring, etc. So if we're voting; I'm a carb kinda guy ... #### Armilite ##### Well-Known Member I put 359,500 miles on a New 1979 Chevy 350 EFI that I ran 91 Octane 10% Ethanol most of its life when it finally spun a Bearing. I ran a can of Seafoam thru it just before Winter and also changed the Fuel Filter just before it got Cold. Otherwise, the EFI was never touched. EFI used on Planes eliminates Carb Icing, and gives you a smoother Starting and Running Engine with a little better gph. The stoichiometric mixture for a gasoline 4 Stroke engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air-fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required. For a 2 Stroke Air, Fuel, Oil it's around 12.2:1 - 12.5:1. #### TiPi ##### Well-Known Member Log Member I put 359,500 miles on a New 1979 Chevy 350 EFI that I ran 91 Octane 10% Ethanol most of its life when it finally spun a Bearing. I ran a can of Seafoam thru it just before Winter and also changed the Fuel Filter just before it got Cold. Otherwise, the EFI was never touched. EFI used on Planes eliminates Carb Icing, and gives you a smoother Starting and Running Engine with a little better gph. The stoichiometric mixture for a gasoline 4 Stroke engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air-fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required. For a 2 Stroke Air, Fuel, Oil it's around 12.2:1 - 12.5:1. Only 1/2 the story: ALL engines have 14.7:1 (14.7000:1.0000 ) as the stochiometric mixture (Edit: using normal petrol). 4-strokes & 2-strokes deliver max power in the range of 12-13:1 (rich) and best economy 15-18:1 (lean). The possible max lean mixture is greatly dependent on combustion chamber design, mixture quality and gadgets installed to control detonation. 2-strokes are being run with rich mixture to prevent piston over-heating (fuel-cooled). This is from the Hirth EFI manual, no info on faults/fault codes: Last edited: #### dwalker ##### Well-Known Member Well I am an EFI guy, so I will always lean in that direction. As a couple points of fact, EFI engines can and do run on mechanical- engine driven- fuel pumps, usually off the end of a camshaft or a Gilmer belt on a pulley arrangement. The entire rest of a proper EFI system is somewhere along and order of magnitude more reliable than a conventional coil/distributor or magneto ign with a carb. If done anywhere near properly you use a coil per plug, and an injector per cylinder. In the case of a 2-cylinder engine, you could use a single point injector with a redundant "fail-safe" injector fitted as well, which might actually ease tuning. While injectors "can" clog, unlike a carb they rarely if ever clog to the point the engine will not run, it just runs a bit rough. No carb ice. No loss of power from carb heating the intake charge. The list goes on. I would shoot Ross at SDS a message and see what he can do for you. #### Lucky Dog ##### Well-Known Member ============================= Do a little Math. Aerolite 103 with the F33 (28hp) is 235 lbs. Hirth F33 with Electric Start is 45 lbs. 235 lbs - 45 lbs = 195 lbs for Airframe. F23 50hp is 78 lbs + 195 lbs = 273 lbs, including reduction unit, full exhaust, and electric start or 71 lbs + 195 lbs = 266 lbs with recoil start reduction unit and full exhaust, so to make Part 103 254 lbs + 24 lbs = 278 lbs Max with a$4000+ BRS Weight Allowance. While you get 24 lbs Allowance for the BRS, it still Weighs probably 18-20 lbs.

A BHP of 50 at sea level and Elevation of 2300 feet is 3.45 HP loss. 50hp - 3.45 = 46.55hp!

Aerolite 103 MTOW 600 lbs = 272.1554 kg / 10 kg = 27.21554 kw needed to Fly Well = 36.49664 hp!

F33 is 313cc/7cc= 44.7hp is Possible with a Good Tuned Pipe using 11.5cr. With the Hirths 9.5cr - 2hp = 42.7hp.

EFI on these Small CC Engines don't make you more hp, but may Improve your GPH use. Hirths EFI SUCKS, You can't Tune it, you have to take it to a Dealer.

Mega Squirt or Ecotrons make some nice EFI Setups that You can Tune. IF, you Read both of their Websites you will learn a lot about EFI and LOOK at their Photo's and you can Sorce most of the Parts much Cheaper. Lots of 2000+ Sled Engine have EFI.

For Flying out of Higher Elevations, a Turbo with a variable Boost Controller would be nice. Say for Takeoff use 3-4 lbs then reduce it to 1-2 lbs.

A Stock 670 was [email protected] 669.2cc/7cc= [email protected]

SKIDOO 670 TURBO 11 lbs BOOST at 6750rpm = 163.4hp!

1996 MX Z 670 TURBO 9 lbs of BOOST. [email protected], [email protected]

1996 MX Z 670 TURBO 7 lbs BOOST. [email protected], [email protected]
95hp to 106hp = 11.5789% increase!

Weber makes some nice EFI Throttle bodies and so does SFS.

The F23 is 78 lbs, including reduction unit, full exhaust, and electric start or 71 lbs with recoil start reduction unit and full exhaust. I believe the Kawasaki 440 is 7 lbs lighter than the Rotax 447UL. The Kawasaki 440 with a Good Tuned Pipe Dynoed making [email protected], [email protected]. Kawasaki 440 is 435.9cc/61hp= 7.145cc to make 1hp. 435.9cc/7cc= 62.2 [email protected]
So, if the F33 actually weighs 71 pounds and we recalculate, there's plenty of room to upgrade to the F23 and stay within 103 weight. 50 hp could fly a 190 pound pilot in that airplane at 10,000 MSL

#### Armilite

##### Well-Known Member
So, if the F33 actually weighs 71 pounds and we recalculate, there's plenty of room to upgrade to the F23 and stay within 103 weight. 50 hp could fly a 190 pound pilot in that airplane at 10,000 MSL
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First, for the Aerolite 103 they say 235 lbs with the F33 28hp, they don't Specify if with or without the Electric Start. So Airframe could be 190 lbs - 195 lbs.

F33 (28hp) Specs.

No, you got it backward, the F33 313cc (28hp) is 45 lbs with Belt Drive & Electric Start & Exhaust! It's 40 lbs without Electric Start.

The Aerolite 103 with the F33 313cc (28hp) is 235 lbs - 45 lbs = 190 lbs for the Airframe. Has an MTOW of 600 lbs.

If Airframe is 235lbs + 30 lbs (Gas) + 190 lbs (Pilot) = 455 lbs = 206.3845 kg / 10 kg = 20.63845 kw needed to Fly Well = 27.67662 hp!

F33 (28hp) 313cc/7cc = 44.7hp if you use a Good Tuned Pipe with 11.5cr, Proper Size Carb/EFI and turn it 6500rpm. +/- 1.0cr = 1.0hp. So with Hirth's 9.5cr -2hp =
42.7hp is possible. A MTOW of 650 lbs needs 40hp to Fly Well.

There is an upgraded Head for the F33, more Mass! I believe it adds 2 lbs. If you use all of the different Engine Coatings you can reduce your overall Temps by 20%.

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F23 (50hp) 521cc Specs.

Aerolite 103 Airframe = 190 lbs + F23 (50 hp) 71 lbs without Electric Start = 261 lbs - 254 lbs = 7 lbs to Heavy, so NO, it doesn't make Part 103 unless you put on a $4000+ BRS for it's 600 lb MTOW. You get I believe 24 lbs for the BRS Exemption. The BRS for 600 lbs I looked at a few years ago was 18 lbs. 24 lbs - 18 lbs = 6 lbs. Is there other BRS out today with less Weight, maybe. I wouldn't want an Engine without Electric Start myself. In Truth, 36hp will Push/Pull most Part 103 Airframes past the 55 knots Full Power Speed. ======================================================= A Good Used Rotax 277UL 55 lbs to 65 lbs depending on configuration, Cost$250 to $650 usually with the Gear Drive! Rebuild kit less than$200.

268.8cc/7cc= 38.4hp@6500rpm is possible!

277UL with Gear Drive Rebuilt $850.00 <--- I Paid$250 for my last 277UL with a Gear Drive, so $450 Rebuilt. Avg Custom Tuned Pipe for 36-38hp.$650.00 <--- Can you make your own, Yes!
Engine Coatings Avg. $350.00 <--- Can you do your own Coatings to Save $$, Yes. -------------------------------------------------------- Total 1,850.00 You can Big Bore the 277UL to Max (82mm x 66mm) 348.6cc / 7cc = 49.8 hp! A Custom made Big Bore Sleeve Avg 180, the last Blank Sleeve I bought for 82mm off eBay was 40 to make your own. Custom-made 82mm Piston 180. An Off the Shelf 82mm Piston Avg 80. I would use the 670 HO Twin 82mm Big Bore Piston and use the 670/670 HO Longer 132mm Rod which gives it a better Rod Angle and Bigger Bearings with a Special Base Gasket Spacer, 40. Cylinder & Case Porting can Gain you 10-15% more hp. Avg Cost to have done is 350, can you do it yourself, Yes! ====================================================== F33 w/Recoil Start 4255.88 F33 w/Recoil Start & Belt Reduction Drive 5285.88 F33 w/Recoil & E-Start w/Belt Reduction Drive 5785.88 Avg Custom Tuned Pipe for 40-42hp. 650.00 Engine Coatings Avg. 350.00 F33 w/Recoil & E-Start w/Belt Reduction Drive 5785.88 ---------------------------------------------------------------- Total 6,785.88 ===================================================== F23 (50hp) F23 w/Electric Start & Carburetor 9,140.63 F23 w/Recoil Start & Carburetor 8,599.50 F23 w/Electric Start & EFI 11,158.88 F23 Belt Reduction Drive 1,377.68 Optional Oil Injection 415.00 Engine Coatings Avg. 350.00 + BRS 4000.00 F23 w/Electric Start & Carburetor 9,140.63 F23 Belt Reduction Drive 1,377.68 Optional Oil Injection 415.00 --------------------------------------------- Total 15,282.68 For EFI Upgrade. + 2,018.25 ---------------------------------------------- Total 17,300.93 #### byGeorge ##### Well-Known Member Not even penicillin can cure fuel infection... #### Armilite ##### Well-Known Member Only 1/2 the story: ALL engines have 14.7:1 (14.7000:1.0000 ) as the stochiometric mixture (Edit: using normal petrol). 4-strokes & 2-strokes deliver max power in the range of 12-13:1 (rich) and best economy 15-18:1 (lean). The possible max lean mixture is greatly dependent on combustion chamber design, mixture quality and gadgets installed to control detonation. 2-strokes are being run with rich mixture to prevent piston over-heating (fuel-cooled). View attachment 124899 This is from the Hirth EFI manual, no info on faults/fault codes: View attachment 124898 ============================ As your Graph shows, for Max Takeoff, as I said, a 2 Stroke needs to be at 12.2 to 12.4 as your Graph shows. Can you tweak it after Take Off for a better gph, Yes! #### Armilite ##### Well-Known Member The stoichiometric mixture for a 4 Stroke gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required. The ideal air-fuel ratio is 14.7 parts air to one part fuel. But that's in an ideal world, one where every molecule of fuel and oxygen is completely consumed during every single combustion event. In a real engine, a 14.7:1 air-fuel ratio is a little too lean. Best performance for most vehicles is in the 12.5 to 13 AFR range. Going too rich will have the opposite affect and decrease your performance. Getting up to cruising speed or getting ready to pass someone, you usually are looking for the performance to get up and go. For 2 Strokes you have GAS + AIR + OIL making up the Mixture. That's Why 12.2-12.4 is Best. #### Armilite ##### Well-Known Member AFR TABLE. At 6000rpm 12.2 to 12.5. The Higher the rpm used the Richer it needs to be to Cool the Combustion Chamber. For Aviation 2 Strokes turning 6500rpm on Take Off, 12.2 to 12.4 is Ideal depending on Temperature, & Altitude. Mega Squirt - Principles of Tuning Programmable EFI Systems. #### TiPi ##### Well-Known Member Log Member The stoichiometric mixture for a 4 Stroke gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required. The ideal air-fuel ratio is 14.7 parts air to one part fuel. But that's in an ideal world, one where every molecule of fuel and oxygen is completely consumed during every single combustion event. In a real engine, a 14.7:1 air-fuel ratio is a little too lean. Best performance for most vehicles is in the 12.5 to 13 AFR range. Going too rich will have the opposite affect and decrease your performance. Getting up to cruising speed or getting ready to pass someone, you usually are looking for the performance to get up and go. For 2 Strokes you have GAS + AIR + OIL making up the Mixture. That's Why 12.2-12.4 is Best. 1-2% of oil changes the stochiometric ratio bugger-all of nothing, as oil is also composed of hydro-carbons, just a bit heavier. But the 14.7:1 ratio is based on MASS, not volume. Max power is between roughly 11.5 and 13:1, depending more on combustion chamber and mixture preparation etc than 2 vs 4-stroke. #### Armilite ##### Well-Known Member 1-2% of oil changes the stochiometric ratio bugger-all of nothing, as oil is also composed of hydro-carbons, just a bit heavier. But the 14.7:1 ratio is based on MASS, not volume. Max power is between roughly 11.5 and 13:1, depending more on combustion chamber and mixture preparation etc than 2 vs 4-stroke. ============================================== My Info was from Skidoo Racers using Skidoo/Rotax 2 Strokes with EFI, who say 12:2-12:4 AFR. Your broad 11:5 to 13:1 which 12:3 falls right in the middle my 12:2 - 12:4 kinda proves my point. Oil added to the GAS does change the AFR. The Oil is for Lubrication. #### flyby50 ##### Member Had several boats with 2 strokes some with carburetors later with EFI. I preferred EFI could leave it sit all winter and it started every time. Carburetors get gummed up easier all I had to do with my EFI engines is dump a pint of gas saver in the last few gallons in the tank run it for 30 minutes. Then I would drain the header tank. With the EFI really wasn't anyplace to get fuel and oil gummed up as long as you drained the header tank. Taking the boat up to 8000 feet no problems with EFI. I would go with EFI Hirth engines are from Germany, so I know the engineering is good. #### Armilite ##### Well-Known Member Had several boats with 2 strokes some with carburetors later with EFI. I preferred EFI could leave it sit all winter and it started every time. Carburetors get gummed up easier all I had to do with my EFI engines is dump a pint of gas saver in the last few gallons in the tank run it for 30 minutes. Then I would drain the header tank. With the EFI really wasn't anyplace to get fuel and oil gummed up as long as you drained the header tank. Taking the boat up to 8000 feet no problems with EFI. I would go with EFI Hirth engines are from Germany, so I know the engineering is good. ============================================ Hirth's EFI Sucks from everyone I have talked to, you have to take it to a Dealer to make any changes. I would rather have full control of the EFI Tuning. The F33 has had a problem with Over Heating. They finally made a better Head for it for more$$$\$ you can buy. Still Sell it with original Head. I don't call that good Engineering. Some other Hirths have had problems also. Rotax was very Slow about making any upgrades, Gray Head vs Blue Head, Ceramic Water Pump Seal, Cageless Rod Bearings.

I got an Ecotrons EFI kit to try on a 277UL, just haven't found the time to play with it. Mega Squirt makes a nice setup also.