[Dcheck]

A question, I have a OS 61 Sf pumped with the OS 86 carb with a butter fly valve. Why did OS put a butter fly valve on this engine? Are butter fly's better than barrel valves? I have crawled around the internet and have some information on the engine but not the reason why it was done this way.
Thanks in advance

[cassat]

Less intake airflow restriction and your throttle will be more proportional between open and closed. If you look at a YS 61 classic pumped engine, you will see the same thing.

[Dcheck]

I read that, also the opening is on the large size. So why not use butterflys in all engines?

[stegl]

The butterfly barrel may require a pump as less suction at that point for consistent runs . Other manufacturers may not want to venture there as the price climbs with added expense of a pump.
As Dave mentioned re YS as they use a regulated pressurized tank system ; about the same as a pump.
Perry had to develop their own special carb to work in conjunction with their pump to work well and it did .

[RAMJET]

High performance planes benefit form a pressurized system by providing constant fuel pressure at all attitudes , A pressurized system requires a different and more accurate metering system(carb) to control the pressure .. the pumped system is more complex and harder to setup but has some advantages . I don't think one would breath any better then the other but the pump would work better in harsher conditions or where consistency is a must .. .

[Gizmoman]

Go here for details.
http://sceptreflight.com/Model%20Eng...%2061SF-P.html

[Dcheck]

I learned something
Thanks