Frequently Asked Questions

Size | Transfer Slots| Air bleeds | Fuel Lines| Ignition | Methanol | Horsepower | CFM | Main jets | Anodizing | Air Cleaner | Is this carby suited for standard engines or racing? | Cleaning | Fuel Levels | Fuel pressure | Spare Parts |

What size carby do I need?

The CFM consumed varies depending upon the efficiency of the engine. Engines fitted with SmartCarby run more efficiently and produce more power for the same CFM of consumption as other carobs. Most of the powerful engines to date have produced maximum power with air fuel ratios ranging from 13.4 to 14.2 to one. 12.8 to 1 is definitely too rich for maximum power production with a SmartCarby. The vaporization and the burn speed in the chamber is far superior to other carburetors resulting in highest power occurring at closer to stoichiometric ratio than previously thought.

To work out the CFM consumed by the engine multiply the horsepower by the CFM factor in the chart below.

Here is a list of AFR’s and the calculation factor. These factors assume an engine B.S.F.C. of 0.4 lbs/hp/hr. which is average for a modern engine build.

The SmartCarby is rated to supply the necessary CFM’s at less restriction to the engine than the Holley CFM rated restriction commonly used. Thus a 650 CFM SmartCarby is approximated for a 558 HP. engine on gasoline. If the engine is more efficient than 0.4 lbs per horsepower per hour then the power figure is higher. The power figure is not the maximum power capability of the carby.

What does a Transfer slot do?

The transfer slot is a short slot that is positioned at the throttle butterfly location. Fuel for the low power operation of the engine flows from this slot. The power range of fuel supply is typically from idle rpm up to approximately 25 horsepower. The upper point of the transfer slot controls the fuel delivery prior to main jet operation. The lower point of the transfer slot controls the fuel delivery of how it crosses over from idle to low loads as you slowly move away from a stationary position .

The transfer slot design is VERY important to the smoothness, economy and power production of the engine. The transfer slot of a SmartCarby is removable for ease of tuning, this is a feature not available on other carbs. This removable feature enables the low load fuel flows to be precisely matched to your camshaft. And if you change cams you only have to replace the insert, not the whole base plate or carburetor as in other cases.

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What does an air bleed do?

Only the idle transfer system of the SmartCarby has air bleeds. The mains does not have an air bleed. The transfer air bleed controls the vacuum level and the airflow in the passages of the transfer system. A larger air bleed slightly reduces vacuum and greatly increases the volume of air flowing in the holes and channels creating better atomization of the transfer fuel. The air bleeds also stop the fuel from siphoning from the bowls into the manifold when the engine is stopped.

Do I need to change my fuel lines?

Standard dash 6 (3/8 th NPT) fuel fittings screw directly into the fuel inlets on the ends of the bowls. Elbows may be used to alter fitting directions.

How do I convert from methanol to petrol? I want to store my engine by running it on petrol after it has been raced on methanol.

Petrol requires much smaller jets than methanol. There are options you can take. You could purchase another jet plate and swap it to one fitted with petrol tune settings or even an entire top plate assembly and simply change to petrol with one bolt or you could change the idle/transfer jets with a screwdriver and run it for a time on petrol prior to storage. If you wish to run high loads you will have to change the main jet as well by removing the aero plate and dropping in petrol tuned main jets.

How much power increase will I get?

The increase in power is relative to how bad your previous carby was. Some engines have shown on the race track a 10% increase in power e.g. from 865 to 951 hp exerted. Others have shown less but all have improved. Engine dyno tests have yielded original figures of 474 hp increasing with the SmartCarby to 500 hp. The horsepower increase is not the only benefit from the SmartCarby. The water temperature always drops and the exhaust temperature is colder.

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How come your carby is smaller CFM than others?

We rate them at a vacuum restriction that is closer to the real world restriction occurring in most engines therefore the CFM number appears less.

How do you change the main jets?

You undo 2 screws and remove the aero plate from the jet plate and lift out the old jet by hand and drop in the new one. You do not drain fuel to do this.

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What air cleaner fits?

Standard 4150 style Holley air cleaners fit. Some ultra low profile cleaner bases interfere with the bowl. We recommend the Moroso brand bases.

Can I anodize it?

Yes. The SmartCarby is 6061 T6 aluminium therefore any colour that is used in anodising can be done to the SmartCarby. Unlike die cast the aluminium is well suited to polishing. This looks stunning on show cars and hot rods

Will it suit my standard engine or is it a racing only carby?

The carby is tuneable for any engine, it is very quick to convert from one set-up to another. It is as simple as undoing one bolt and slipping on another CFM sized top. You can drive your car to the shops or take it down a drag strip!

Is it easy to clean the carby internals?

Yes. All passages are easily accessible and all holes are straight through for easy cleaning.

At what height do I set the fuel level?

The fuel level is set by adjusting the needle and seat so that the float arm is horizontal in the fuel off position. This will result in the level being approximately 5 mm below the surface of the body. The pressure you run alters the fuel level.

What ignition system is best to get the most from my SmartCarby?

The amount of ignition energy that crosses the plug gap is partly determined by the resistance of the gap. When the vaporization level is high as in the fuel condition created by the SmartCarby, the resistance across the gap is higher than with other carbs. This increased resistance sometimes results in not enough energy from a weak ignition system to allow good tuning of the engine, especially at low revs. It is not the fault of the carburetor but the fault of the ignition.

We recommend using a multiple spark capacitor discharge ignition system. An MSD 6AL is suitable for street engines 350 HP, MSD 7AL-2 is suitable for 500 HP or a Crane HI-6 with a Crane race coil is suitable for just about anything. We recommend using the correct coils for all the ignitions. If you do not use a powerful enough ignition, the full benefits of the SmartCarby will not be released. An engine running a points style Kettering ignition or a standard inductive electronic ignition will not give its maximum power potential..

What fuel pressure can I run?

A viton tip (petrol type) needle and seat of 0.110” diameter will easily hold 12 lbs fuel pressure. Larger diameter needle and seats hold slightly less.

Where do I buy spare parts?

All the spare parts for the SmartCarby except for the main jet and gaskets are standard Holley style replacement parts and can be purchased from any performance shops around the country. QuickChange SmartCarby's are designed with reusable gaskets and the billet bodies never go out of shape. With correct usage this carby will never need reconditioning.