fbpx
Login

 

Jump to Forum..

why two carbs

in 912 / 914 Technical Questions 7 years ago
Why did Rotax employ two carbs on the 912 series? For the same power, Jabiru uses a single (larger) Bing. Were they having fuel distribution imbalances they couldn't solve?

  • Re: why two carbs

    by » 7 years ago

    Hi Karl,
    Because you do get more power with two and more efficient. Jabiru with one isn't efficient and could get more power with two, but that would take up more space, more weight and more engineering. Jabiru is just a simple design. When Ultralight aircraft first came out all the engines were single carbs. Then later on to get more power they added a second one.
    I used to fly those swing seat, single cylinder 15 hp Yamaha engines. Then 2 cylinder single carbs came to be and then two cylinder twin carbs.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: why two carbs

    by » 7 years ago

    Yes, many race car engines, in the carb era, used multiple carbs. I think it was to reduce air drag from longer runners. Since the 912 series has higher specific outputs, perhaps this was the problem.
      
    Report

  • Re: why two carbs

    by » 7 years ago

    To sell twice as many parts?..... joking.....maybe.
      
    Report

  • Re: why two carbs

    by » 7 years ago

    I see today Sonex is recommending their "AeroInjector" as a proven, single carb solution for the 912. (I'm not making this up!) The installers wanted to be able to fly inverted. It'd be interesting to see the performance hit from that installation.

    I'd stick with the Bings. The Sonex is a very crude carb which requires the pilot to monitor the EGT on changes in power and altitude.
      
    Report

  • Re: why two carbs

    by » 7 years ago

    I talked with a Sonex builder this morning. He has a friend with the Jabiru six and the single Bing. He said fuel distribution was quite poor in the engine, with wildly varying EGT and CHT. Jabiru's recommendation for evening it out some didn't work.

    I'll assume Rotax chose two carbs so they could push the wee engine harder. Once synched, the two should keep the distribution relatively even, and this would allow them to run at higher outputs with less chance of one hot cylinder. Also, according to the hot rod sites, short runners aid in power at higher revs.

    Case closed?
      
    Report
You do not have permissions to reply to this topic.
Related Topics
Title Category Replies
No 912uls carbs in US?! Rotax-Owner Community 1
Fuel line setup dual Bing 54 carbs 2 Stroke Technical Questions 4
Carbs General Tech Discussion 6
912UL CV carbs without airbox-what is the fix for the lean running ? 912 / 914 Technical Questions 28
Problem Adjusting Carbs on 912ULS 912 / 914 Technical Questions 2
Follow Us

Recent Videos

Safety First!

 

To receive critical-to-safety information on your ROTAX Engine, please subscribe to
ROTAX-OWNER.COM

Prize Giveaway!


SUBSCRIBE NOW
to automatically enter this years draw!

Login