Number of Carburettors

[bilby54]

Does anyone know why Rotax uses two carbs for most of its engines?

 

The setup on the engines is such that each side of the engine is fed by a separate carby and is essentially two 'separate engines' on the same crankshaft or is that not the case.

 

The Jabiru engine works with a single carb of the same type as the 912 Rotax.

 

Just wonder if anyone has any info why this is.

 

 

[blueshed]

Thats a Good question and am sure there are many reasons, possibly including!

 

A more simple intake manifold system.

 

Two small venturi's may control and atomise the air-fuel mixture better!

 

You get more practice rebuilding and tuning two carby's.

 

Twice as many airfilters to clean, twice as many carby heats to set up etc

 

 

[Ultralights]

both carbies on the 912 are fed from a single airbox, so its only 1 airfilter, and the carby heat is only a single tube running from the exhaust to the airbox.

 

 

[Guest Crezzi]

both carbies on the 912 are fed from a single airbox, so its only 1 airfilter, and the carby heat is only a single tube running from the exhaust to the airbox.

It depends on the installation. On most trikes theres no airbox so seperate filters for each carb & the heat is simply coolant pipes to a manifold block - no setup required.

 

Cheers

 

John

 

 

[crashley]

It may be Redundancy If you have a problem with one carby you will still get some power out of your engine but most likely you get a better mixture out of two small carbs than one large one

 

 

[dazza 38]

It depends on the installation. On most trikes theres no airbox so seperate filters for each carb & the heat is simply coolant pipes to a manifold block - no setup required.Cheers

 

John

Same at Boonah with the tecnams, they dont have a heat box, or carby heat for that matter, due to filters drawing warm air, from the engine bay.They lose about 5 hp, by drawing warm air.They run sperate air filters.

I dont know the answer for above question, but most of road bikes, have individual carbies, or fuel injection per cylinder, i think it is for performance. Although it is/was a real hassell, to balance multiple carbies.

 

 

[jetboy]

2 carbs no good for redundancy on the 912 when one carb falls off the engine wont run too good I saw this happen and the plane had to be pushed off the runway couldnt even mange a taxi back to the pits

 

Ralph

 

 

[pylon500]

Actually I think a better question is why does the 3.300lt Jab run on only one carb when Rotax thinks it better for their 1.200lt engine to run on two? :csm:

 

 

[Yenn]

The less number of cylinders per carby is usually considered to give better performance and it seems to apply to cars, but the requirements for aircraft are different. We do not need instant response from any rpm for overtaking, just a steady speed usually and the single carbs on aero engines are pretty good but not perfect. Better still is injection.

 

 

[bilby54]

Actually I think a better question is why does the 3.300lt Jab run on only one carb when Rotax thinks it better for their 1.200lt engine to run on two? :csm:

Could also ask why the Rotax 503 has only one carb while the 582 has two with a fair bunch of gear whizzing around inside to control them.

 

The 912 engine also has a 1/2" balance line running between the two manfolds to add more interest. Don't get me wrong, the carbs on top of the engine are much easier to work on than the Jabiru location but I think that it would be a brilliant set up with just one carb (or injection system) so was just wondering why two?

 

 

[Guest Crezzi]

Rotax 503 were available as either single carb (SCDI) or dual (DCDI). IIRC the dual carb had about 5hp more

 

Cheers

 

John