Bing 45 on a Mac

[joeheli]

Has any one adapt a Rotax carb.(bing 45) to a Mac? I really don't see it imposible.

[Chuck Irby]

Jose, since no one else has replied to your question, I will. However, I am not familiar with the Bing 45. Is it a down draft carb?

My 618 has two Bing 54's on it, and I am well pleased with them. But, since they are side draft carbs, it would be difficult to mount one of them on a down draft manifold, IMO.

[joeheli]

Thank you for your reply Chuck :D ! .I think the 503 rotax has them and they mount it side draft .

[Chuck Irby]

Why would you want to mount a side draft carb on a down draft manifold, Jose? There are plenty of good down draft carbs available. What carb do you have on it now, and what is it that you don't like about it?

[joeheli]

I Have a Holley 1920. Becouse I have heard, that "if we coud adapt a Rotax Carb to the mac, the Mac will be more reliable"

[Chuck Irby]

Hmmm, if I were you, I would contact GyroMike. He probably knows as much about the Mac and it's carburation as anyone. Maybe he will recommend a different carb. But it seems to me that the carb you have, in good shape, should be reliable.

Jose, I think you meant the Bing 54, instead of the 45. My son has a Rotax 503, and I am pretty sure it has Bing 54's on it also, just different jetting than mine.

[joeheli]

Chuck I was thinking something like this sketch that I made:... Guys this is only a scketch!

[joeheli]

Oh !! sorry, yes is Bing 54.

[Chuck Irby]

Jose, there is no doubt that a side draft carb can be mounted, with an adapter, to a down draft manifold. But, I still think there are much better alternatives. I have run a lot of Holley's over the last 40 years and have never had any major problems.

If I were you, I would send a private message to Mike or someone who is thoroughly familiar with the Mac and it's fuel system.

[joeheli]

Ok Chuck, I wil send it the email to Mike I think the same thing about my Holley, but maybe with experience with clear that for me . Thanks for helping :D !

[gyromike]

Jose/Chuck,

I don't know much about Bing Carbs...othere than that they are used on Rotax engines.

But a 503 uses 2 Bing 54's, and it 503 cc's (30 cu.in.)
A Mac is 1638 cc's (100 cu.in)!

A single Bing 54 may not be enough carb for the motor.

The Mac will flow 208 Cubic Feet per Minute (C.F.M.) at 3600 rpm (Assuming 100% Volumetric Efficiency).
A Rotax will flow 115 C.F.M. at 6500 rpm, about half of the Mac.

What is the CFM rating for the Bing 54?

[joeheli]

OK now I understand why Rotax use 2 Bing 54 there engine, But now I know that is not enouth carb for a Mac . Thanks Mike for clarify me. What woud I do with out you guys!.

[Chuck Irby]

Thanks Mike. Do you know of any problems with the Holly 1920? Mike,what carb are you running on the your Mac?

[gyromike]

Chuck,

I run the Holley 1940 dual-float instead of the single-float 1920.

It's what I had when I built the machine. Maybe a Bing or Mikuni would work better if it could flow enough, but I don't know for certain. Might be a project for a later date.

[joeheli]

Mike, Rick told me that the 1940 was the one that I shud get, But it is imposible to get. Do you know who is selling one?

[Rick Whittridge]

Mike, Rick told me that the 1940 was the one that I shud get, But it is imposible to get. Do you know who is selling one?
Jose,I was told that the 1940 was not being made any more by a factory HOLLEY MAN not that they where not availible.If you look around the auto parts stores you might get lucky.Ford 6 cyl,AMC 6cyl used these carbs.If you find one keep in mind that the carb has to be modified from the CAR mode to the GYRO mode.I have rebuild kits & can preform the mods for you.

[Chuck Irby]

Thanks Mike.

Jose, If you can't find the Holley type 1940, you might want to at least consider a 2 barrel outboard motor carburetor before the single throat Bing. It's still a side draft, but it would flow enough air for your engine. I never had any problem with them back when I was racing outboards. The Mercury, OMC and Yamaha all had great dual throat carbs. You should be able to find one of them cheap there on your island. If you do, look for one off of a big V6 or V8 outboard. Of coarse, you'll still have to build an adaptor.

[joeheli]

Thank you guys for you good info..

[Chuck Irby]

Well . . . Mike was your biggest help, Jose, as I knew he would be, especially with the Mac. Is your intake conducive to adapt a 2 barrel carb to? Just wondering if you would have to find another intake also. Let us know what you wind up doing.

PS, I did find a 1940 or two in the Internet. But they were weigh too proud of them.

[joeheli]

I think I will try to get the 1940.

[joeheli]

Hey Chuck how much they will asking for?, and ,Were did you find it?

[darrellwittke]

I thought I read somewhere on Norm's forum you could reinforce the 1920 float with a thin line of epoxy (which changes and dampens the harmonic frequency and reinforces the float metal. Is this not correct? (Guess we will find out since it's what I've done to mine. 42 hrs on hobbs now I think.)