• Homebuilt Airplanes is a vibrant community of pilots, plane builders and industry experts. Our thousands of active members use HBA to trade detailed technical information, discuss best practices, share their builds, plan get-togethers and buy/sell planes & parts. In addition to the community you gain access to, you gain access to over 20 years of curated knowledge by some of the brighest in the industry.

    Access to HBA is subscription based. It is free for 7 days so you can get to know our community!

    Click Here to Become a Member and Access HBA

Bing 54 jet size adjustments for altitude

Jay Dub

Well-Known Member
Dec 17, 2019
I have plenty of experience dialing in motorcycle (2 & 4 cycle) and chainsaw carbs.

I have a 447 Rotax with the single factory Bing 54 carb that I just put new seals and gaskets in that I will be installing on a Kolb Firestar II. The Bing is stock with the 165 main. I live at 4600'msl so I need to lean it some and I've looked at charts such as this bing chart and I'm thinking I'll use the sizing factor of .96 (4500', 59F) as I will be a little rich in the heat of summer but good enough even at 45-50F. I doubt I'll fly the Kolb in colder weather than that.

165 x .96= 158.4. I can buy a 158 main jet, so a perfect starting point. That doesn't help me with the sizing of the idler jet or needle jet. The main jet controls the max fuel at WOT. The needle controls fuel in the midrange (has some adjustment via clip). The idler of course deals with idle and transition to mid-range. Do the needle or idler jet typically get changed to compensate for altitude with the rotax 2 strokes? It seems they would be but perhaps with the clip I can drop it enough to get it right in the mid range and the idle air screw might let me dial in the idle mixture. I haven't dialed in a Bing 54 on a Rotax before so asking if anyone has some experience with them.

I will be using a dual EGT gauge when I get ready to do the break-in.

Any good advice is appreciated.