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Mark Boesen's

Nice original Babe Bee from a Super Cub 105, late fifties.



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Bee Venturi diameters

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Bee Venturi diameters

Post  Canso07 on Sun Mar 19, 2017 10:52 pm

Hello,

Just wondering if anyone had a list of venturi bore diameters for the bee backplates or a full cox list of diameters.

Thx Canso.
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Re: Bee Venturi diameters

Post  pkrankow on Mon Mar 20, 2017 7:42 am

It is not just the backplate.  The air passage through the tank is pretty darn, if not more important.  I port the tank to 5/64 which is just a hair smaller than 2mm, and not quite as large as the .082 inches per the Paul Gibeault Mouse race guide

https://coxengines.ca/engine-and-fuel-guides.html

I don't modify my back plates and the engines run well. I use the plastic ones since the metal are getting to be unobtanium.

Phil
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Re: Bee Venturi diameters

Post  Canso07 on Mon Mar 20, 2017 10:01 am

Ok thx pkrankow...just wanted to make sure I'm using the right tank/backplate when building up an engine (example black widow).

Canso.
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Re: Bee Venturi diameters

Post  fredvon4 on Mon Mar 20, 2017 10:11 am

Canso07

Not too bad on this site, so do a search..I would search for you, but I am off to endless mowing duty as soon as I finish this note

I do not fuss with Tanked Bee venturi drilling -----but there are quite a few guys here that do and have experimented with the bask plates

There are several threads about what works and what sizes they started with vs drill out to

I think within the discussion are hints to factory sizes---- and I do know there is a difference based on what engine...

As an after thought... go to Cox International web site and just read the descriptions on the Back plates or some of their specialty engines for hints
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Re: Bee Venturi diameters

Post  KariFS on Mon Mar 20, 2017 11:51 am

I noticed that the short bee tanks can also have different venturi diameters. I didn't measure them because I don't really have an easy way to do so, but the tank with the small venturi was an older model that uses the G-clip reed retainer, whereas the one with the bigger venturi was made for the plastic retainer.

Phil, Thanks, that was good info about the backplates. I was wondering if I should drill them out but knowing the principle how a carburetor works, I was hesitant. I think I'll leave them as they are.

Slightly Off Topic:
I noticed quite a big difference in rpm when I was experimenting with mufflers, heads and tank extensions last summer. The Babe Bee with the tight venturi and a tank extension was difficult to get past 11.000 with a muffler, 6x3 Kavan and 10% nitro (not ideal setup for bees, I know), but the other one with the large venturi and without the tank extension went easily past 13500 with muffler, same prop and fuel. Both engines had the "yes drag" (as opposed to "no-drag" Wink ) starter spring arrangement and slit-exhaust cylinders. Of course I noticed the difference in venturis only after the tests and not when I was assembling the engines DAMMIT! I think I'll drill one of my tank extensions to the larger diameter and try it again with the large-venturi tank. Another note, a Tee Dee head did not improve the top rpm, only made the engine more difficult to adjust Huh...

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Re: Bee Venturi diameters

Post  Canso07 on Mon Mar 20, 2017 8:54 pm

Thx for the info guys.. I read that the slightly more power reed tanked engines had a 4.37mm venturi diameter at the reed valve compared to the babie bees with a 3.57mm venturi diameter at the reed valve.

Canso.
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Re: Bee Venturi diameters

Post  pkrankow on Tue Mar 21, 2017 7:22 am

The entire air passage profile is different in diameter.  I just drill out the tightest part of it.  I drill it by hand with tape wrapped around the drill bit. Takes a few seconds and WOW is it a performance boost.

Those tank extenders are tricky business.  They may leak air.  They may leak fuel.  If the bee is the smaller size, and the other engine had the larger size air passage that would account for much of those 3k rpm assuming a good tank extender setup.

Phil
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