smartcarb

[BrendAn]

[BrendAn]

these are smartcarb brand carbys.    they are claiming fuel economy and emissions equal to fuel injected 2 strokes. 

supposed to be getting great results on 582 rotax. their main clientele are dirtbike racers.

what i would like to know is if they save up to 30 percent fuel how does it effect the lubrication of a 2 stroke.

fuel injected 2 strokes like the etec outboard pump oil directly to the crank and cylinders. 

these carbs have no jetting either. 

[BrendAn]

CloudForge Venturi™

The SmartCarb's patented CloudForge™ venturi shape lofts and focuses airflow directly at the metering rod, maximizing fuel pickup, atomization, and performance at every throttle position

[BrendAn]

smartcarb.com

https://smartcarb.com

Home – SmartCarb Fuel Systems

 

• SmartCarb is a patented, single circuit, mechanical fuel system that increases performance, improves fuel economy, and reduces emissions. It offers tool-free tuning, …

  Shop

  Select your Year, Make, & Model to find the right SmartCarb for you. Don't see …

  How It Works

  How it works Form Meets Function Take a deeper dive into the core …

  Racing

  Race winning performance Up your game with SmartCarb Top-level racers …

  About

  SmartCarb Fuel Systems was founded by two-cycle engine expert, inventor, and …

  Tech Support

  SmartCarb Fuel Systems pre-calibrates and configures every SmartCarb …

  Orders & Returns

  SMARTCARB RETURN POLICY Orders & Returns We are committed to ensuring …

[Thruster88]

It has a flat needle instead of the round needle in the bing 54. 30% less fuel, I am very sceptical. 

[BrendAn]

1 hour ago, Thruster88 said:

It has a flat needle instead of the round needle in the bing 54. 30% less fuel, I am very sceptical. 

reading a couple of reviews i found , they said they saved  fuel but how would it effect a 2 stroke with 30% less oil. 

as i said above the fuel injected 2 strokes pump oil to the critical areas .

[Thruster88]

You could just mix in more oil to get the same oil rate per hour. Less fuel normally means higher EGT  and or a hole in the piston. 

[facthunter]

Not radically different to many other slide Carburettors. Mikuni. Amal etc The only way to use less fuel is LEAN it out and that Melts/Burns holes in 2 stroke Pistons. This type of carburettor usually sets the standard for straight out Power with ONE per cylinder The difficulty providing richer Mixture when accelerating. Usually done by a well around the Needle Jet or making a Pumper version on some flat slide  designs Parlticularly Snapping open a slide carb can usually Kill the Motor IF done quickly enough.  Nev

[facthunter]

Not a Lot of GOOD 2 strokes are Premix these days. Oil injection is the go. Adding more Oil Makes the fuel more Viscous and the Jetting Has to be altered. It won't compensate for Altitude either. Premix requires  to run all the fuel out  to prevent Left over oil thickening in the carbs when the Petrol evaporates. Nev

[BrendAn]

I like oil injection. Because I mostly run on av gas. No Mogas at West sale.  I only top up the oil tank every 5 or 6 engine hours. I was using Jerry cans with 200ml of oil mixed  in until I was sure the injection pump was drawing oil out of the tank. 

 I like the idea of the smart carb saving fuel but as stated above I can't get my head around leaning out a 2 stroke. Unless  25 to 30 percent is going out the exhaust unburnt.

[turboplanner]

Less fuel = less power. That's acceptable in many stationary engines, but usually an aircraft is looking for more power.

[facthunter]

 IF the Mix has less fuel there will be Unused Oxygen and that will try to oxidise other things like exhaust valves and also Burn slower, and less reliably. Ie May spit Back.. Nev

[BrendAn]

26 minutes ago, facthunter said:

 IF the Mix has less fuel there will be Unused Oxygen and that will try to oxidise other things like exhaust valves and also Burn slower, and less reliably. Ie May spit Back.. Nev

There claim is superior atomisation that sets them apart from bing carbs.

[BrendAn]

33 minutes ago, turboplanner said:

Less fuel = less power. That's acceptable in many stationary engines, but usually an aircraft is looking for more power.

That's not true. It's  how efficient the engine is. Modern injected 2 stroke outboards use a fraction of the fuel the old ones did for the same horsepower. Same with trucks and a lot of cars.

[facthunter]

Anyone CAN CLAIM anything. A CV carb would ALWAYS have better atomisation across the RANGE. An oversize Slide Carb would be even worse.  Hard to tune and little venturi effect.( suction) That type has NEVER been Known for good economy and there's good reasons for that Inherent in the design. Nev

 

[FlyBoy1960]

The old GPT actually has an opinion.

 

Overview: SmartCarb-Style Fuel Systems

What it actually is:
The SmartCarb is a modern, single-circuit mechanical fuel system that uses a patented metering rod + venturi design instead of traditional jets, claiming better atomization, automatic air-density compensation, and simpler tuning compared to conventional carburetors.

Typical claimed benefits (manufacturer):

• ~25–30% better fuel economy vs stock carbs (same conditions and riding style) — SmartCarb quotes this on their FAQ.

• ~8–10% more power due to improved mixture delivery.

• Reduced need for altitude/temperature jetting changes.

• Better atomization and smoother throttle response.

How it works:
• Traditional carburetors use multiple jets and circuits to deliver fuel/air ratios at idle through WOT; SmartCarb uses a metering rod in a precisely shaped venturi with internal float bowl venting to proportion fuel directly to actual airflow.

---

Pros vs Conventional Rotax/Bing Carb

🔧 Pros of SmartCarb-Type System

1) Potential Fuel Savings & Efficiency
Independent tests (on motorcycle engines) saw near-30% better mileage vs a stock carb (e.g., 31.5 mi vs 24.7 mi with same fuel), indicating real world economy improvements under some conditions.

2) Ease of Tuning
• Only a few adjustable parameters (metering rod/Air-Fuel mix) vs jets, needles, and multiple circuits.
• The system compensates automatically for altitude & air density changes better than conventional carbs — no jetting changes needed for moderate elevation shifts.

3) Better Atomization & Throttle Feel (Anecdotal)
Owners frequently report sharper throttle response, smoother mid-range, and fewer plug-fouling issues — especially when stock carbs are poorly jetted.

4) Reduced External Complexity
• No external vent lines.
• Sealed float bowl reduces fuel spillage and evaporative loss.

---

Cons / Practical Limitations

❗ Not Designed for Aircraft Rotax Engines

• SmartCarb products are targeted at motorcycle & powersports two-strokes — sizes listed for 65–500 cc dirt bikes, quads, etc.
• They are not certified or widely used on aviation engines like Rotax 447/503/535 etc.; aircraft carburetion requirements differ significantly and involve strict safety/FAA standards, including fail-to-run criteria that SmartCarb designs don’t meet.

For example, Rotax-owner discussions note that SmartCarb would fail aircraft safety requirements because the linkage design does not guarantee fail-to-run behaviour required for aviation carburetors.

---

🔧 Potential Performance & Tuning Issues

• Some users on dirtbike forums report mixed experiences — from great performance to difficult idling or reliability issues, depending on setup and rider expectations.

• Like any carburetor, incorrect tune, float issues, or installation errors can negate benefits.

---

Two-Stroke Premix & Fuel/Oil Concerns

This is a key point many folks miss when talking about leaner operation:

❗ Two-Stroke Premix Oil Ratio Moves With Fuel
In a premix engine (e.g., a Rotax 447/503/535), the oil is diluted in the fuel. If you lean the mixture (less fuel per air) to save fuel, you also reduce the oil delivered to the engine proportionally — potentially affecting lubrication.

The old pilot wisdom holds that two-strokes are always run slightly rich to maintain cooling and lubrication — the fuel itself carries heat and oil. Going lean to save fuel can raise combustion temps and reduce oil film, which might increase wear or risk seizure, especially in aircraft applications where reliability is paramount.

Oil Injection vs Premix:
• With oil-injection systems, oil delivery can be decoupled from fuel flow.
• On premix engines, any change in fuel flow directly changes the oil ratio.

This is often overlooked in fuel-saving discussions outside aviation — on bikes, it’s less critical because oil injection often handles lubrication ratios, but on premix aircraft setups it’s a safety nuance.

---

Performance Differences (Conventional vs SmartCarb)

On Conventional Carbs (Bing on Rotax)

✔ Proven reliability in certified engines (when properly synced/maintained).
✔ Stable and predictable fuel delivery in certified operating ranges.
✔ Well-understood failure modes and maintenance procedures.

On SmartCarb-Style Systems

✔ Can yield noticeably improved fuel economy and consistent mixture across environments.
✔ May improve throttle response and reduce altitude tuning hassles on small two-strokes.
❌ Not inherently safer or aviation-certified; not predictable under all failure modes required for flight carburetors.
❌ Automotive/moto carbs simply aren’t designed to meet aircraft safety certification.

 

[Thruster88]

The bing 54 is a simple carburetor, I have never had to fiddle with any of mine. Put the recommended jets and needle in and fly. I know a guy who flew his thruster to 18,500 withe stock jets, still climbing @ 200fpm.

[BrendAn]

That is just a collection of comments off different forums. I have already come across some of them.

Smartcarb actually list light aircraft and paramotors as suitable for it.

Chat gtp doesn't realise Rotax have never made a certified 2 stroke aircraft engine. It's a big f##king warning in your operating manual and service manual.

The comment about not going to full throttle when the cable breaks could be fixed with a spring. That one came from a know all on an American forum who could not think of anything else. 

It's the lubrication that concerns me.

[BrendAn]

7 minutes ago, Thruster88 said:

The bing 54 is a simple carburetor, I have never had to fiddle with any of mine. Put the recommended jets and needle in and fly. I know a guy who flew his thruster to 18,500 withe stock jets, still climbing @ 200fpm.

I have never had trouble with them either but it doesn't hurt to look at new options . They might be as good as they say or they might not.

 

[facthunter]

 Premix at Low or closed throttle does not lubricate the Motor adequately. That's well Understood. Going to full throttle is Not a common  set up. Nev

[BrendAn]

16 minutes ago, Thruster88 said:

The bing 54 is a simple carburetor, I have never had to fiddle with any of mine. Put the recommended jets and needle in and fly. I know a guy who flew his thruster to 18,500 withe stock jets, still climbing @ 200fpm.

A side question, what are your static and climb out rpm set too on the 582.

[skippydiesel]

29 minutes ago, BrendAn said:

That's not true. It's  how efficient the engine is. Modern injected 2 stroke outboards use a fraction of the fuel the old ones did for the same horsepower. Same with trucks and a lot of cars.

 

1 hour ago, turboplanner said:

Less fuel = less power. That's acceptable in many stationary engines, but usually an aircraft is looking for more power.

Its a bit of both.

 

My understanding:

• All fuels have a limit to the amount of energy they can deliver ie they can not deliver more energy than their chemical composition contains.
• With the exception of atomic systems (which I don't have a good handle on) all of our other systems involve the interaction (burn) of the fuel with oxygen, which liberates heat and causes the gas to expand (rise in pressure) which can be harnessed to deliver rotational energy or thrust. .
• The amount of O2 delivered, in the form of air, to the burn, will strongly influence the amount of energy released, for a given amount of fuel - thats why we improve air flow and or density (pressure) and use axillary air pumps (turbos & superchargers) often combined with heat exchangers (intercoolers) as cold air is denser (more 02) than hot.
• The burn may also be enhanced by increasing exposure/surface area to the O2 eg atomisation.
• Then there is the ability/efficiency of the system (internal combustion, jet, ?) to turn the energy liberated, into meaningful power, usually expressed as "work".
• The above has been improved with better materials, lubricants, engine design and cooling systems.

 "Modern" engines reflect our improved ability,  to combine the above factors, so that we can harvest more of the fuel energy AND use it more effectively, to deliver more power, which can then be used to reduce fuel consumed for a given output OR more work (however we want to express this).

 

I believe there is a limit to this improvement, that we are possibly close to acheiving.😈

 

 

 

[facthunter]

EVEN fuel Distribution is the Prime method of getting efficiency, Injection is a good way of achieving it. . Nev 

[Thruster88]

27 minutes ago, BrendAn said:

A side question, what are your static and climb out rpm set too on the 582.

6200 static and 6500 on climb. Full throttle level flight is just under the max of 6800. 

[turboplanner]

3 hours ago, BrendAn said:

That's not true. It's  how efficient the engine is. Modern injected 2 stroke outboards use a fraction of the fuel the old ones did for the same horsepower. Same with trucks and a lot of cars.

A.       In-an-engine-we-are-assessing-less-fuel=less-power.

B.       On another engine, say a "modern injected 2 stroke outboard" with its fraction of fuel - if it's given less fuel there will be less             power.

 

Edited 19 hours ago by turboplanner