FAQ's (Frequently Asked Questions)

1. Q: How does the TBI work it appears to be just like any of the other slide type carburetors?

A: Wrong!  The Rotec TBI-40, unlike the others is not a carburetor, it is in fact a mechanical fuel injection system, that self meters fuel supply by use of a cleverly calibrated negative pressure fuel regulator.  This in effect continuously compensates for any variations in fuel pressure and or power requirement.  The other slide types do not do this!

2. Q: How does the TBI 40 unit allow the pilot to adjust mixture in flight, does it use a flow valve like most others?

A: No, the TBI-40 has the most efficient means of adjusting fuel mixture.  Rather that just closing or opening a crude fuel flow tap the TBI-40 works completely different in that it rotates the fuel delivery spray bar though a 90degrees. The spray bar has around 50 tiny holes along its length.  When the holes are rotated to directly face the incoming airstream the engine is at full lean, when the holes are rotated so they are at right angles to the air flow the TBI is at full rich.  It is such a smooth and consistent action.

3. Q: Do I have to keep adjusting the mixture as the fuel tanks get low, or if I change power settings?

A. No, unlike many other fuel systems you do not have to keep adjusting the mixture in flight.  You would typically fly at full rich for the entire flight and at all throttle settings and only lean the mixture in instances where fuel economy is required, cross country etc.  For any given mixture setting the entire range of throttle can be used and this fuel air ratio will be maintained. This ratio is set by the allocation of the 50 tiny holes and where they are located in relationship to the power setting used. More at the top less at the bottom.

4. Q: What sort of fuel pumps do I need to use, can it run on a gravity fed fuel system?

A. The TBI-40 can run at a fuel pressure ranging from 0.5 – 6psi.  This would include gravity fed fuel systems too.  In most cases the typical fuel pumps used on most piston aircraft engine will fall within the correct specifications.

5. Q: What sort of fuels can the TBI-40 run on?

A. The TBI-40 can run on both AVGAS and AUTO gas. However it should be noted that vapour lock is far more prevalent with Auto fuels than with Avgas. In both cases and in particular use with auto fuels, great care must be taken to shield the fuel hoses in fireproof sleeve and keep all fuel items such as fuel pumps and the regulator as cool as possible.  Air blasting these items is recommended. In the case of using Auto fuel a restricted return fuel line back to the main fuel tank is recommended, this will allow any air bubbles that are formed by vapour lock to bleed off back to the fuel tank.

6. Q:. How do you start the engine do you have to use a primer?

A. To start the engine you simply depress the diaphragm override button and this injects fuel into the engine, this can be operated from the cock pit with a simple cable and rocker arm mechanism. After starting the engine subsequent restarts should not require priming.  If the aircraft is already fitted with an existing primer system this can be used too.

7. Q: What attitude should I mount the TBI-40 to the engine?

A. The TBI-40 can be mounted at any attitude and at any angle.  The system has no float so can fly at any attitude. Even upside down. Making the TBI-40 the perfect aerobatic fuel systems.

8. Q:  Where would be the best spot to mount the remote fuel regulator?

A. The remote fuel regulator can suffer from the effects of G forces because these forces will alter the weight of the fuel in the delivery lines.  For this reason it is recommended to mount the TBI regulator no further than 6 inches from the fuel fitting on the TBI’s main body, closer would be even better.  On the Horizontal plain the regulator must be mounted level with the same fuel fitting or even slightly above +2” -00”.   This is important. Do not position the TBI regulator LOWER than the throttle body.

9. Q:  What about fuel filters?

A.  The TBI-40 comes standard with a “last chance filter” this is located inside the main fuel fitting.  It consists of a very fine gauze mesh that is designed to stop debris from blocking the many fine jets.  The airframe is still required to have its own filtration up stream. The TBI-40 in built filter should be inspected and cleaned every 100hrs.

10. Q: Air cleaners?

A. Yes the TBI-40 relies on fine air filtration as unwanted debris and dirt are not only bad for your engine but also can impeded the movement of the slide throttle.

11. Q: What about carb heat I hear that slide throttle bodies don’t ever suffer from ice?

A. Nonsense, any carburetor or throttle body that restricts manifold pressure to control power output, will by nature greatly reduce the local temperature at the throttle opening.  A traditional exhaust heated carb heat system is mandatory.

12. Q: What if I accidentally lean the engine to the point the engine quits while in flight, to bring the engine back to life do I just go full rich?

A: NO! If you lean the engine to the point where it has actually stopped firing, to richen the mixture will probably do nothing as the air speed over the injector spray bar has now become too slow to help even if you go full rich. The best way to bring the engine back to life is to promptly pull the throttle back to idle, if the prop is still wind milling this will immediately restart the engine, then apply full rich and increase power to desired levels. The engine will give plenty of warning that it’s getting towards an over lean state. It will start to run very rough when too lean. Leaning any further will see the engine starve of fuel and stop firing.

13. Q: In the advent of an emergency can the primer override button be used if I suspect the engine has suffered from vapour lock and or fuel starvation?

A: 100% Yes! If you suspect you have vapour lock and or a failure of the fuel delivery system by all means try introducing fuel by employing diaphragm override button. Tests have shown that at full power most engines will continue to run albeit extremely rich with the diaphragm button employed. Definitely something to understand and keep in mind.

14. Q: Are there any advantages in setting the Rotec TBI to run “lean of peak”?

A: Absolutely, there is a saving on fuel and engine life. Contrary to what most think this is where the least temperature is, so it easier on heads etc. On the Bing no one has any idea where it really is so you could in fact be running rich of peak which would raise cruise head temps, also burn more fuel and potentially shorten engine life through excessive unnecessary heat.

Comment: There's some additional comment by Lynn Mattison (Jabiru + Rotec TBI-40-S on a Kitfox) who relays practical results and observations on the Matronics Forum. Goto:

and scroll down to find Lynn's post; its well worth reading.

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