Where does one obtain a 270 venturi for the brodak 40? What size came with the motor? Trying to get a  pattern on a 4 oz tank and have read this motor will do it but with a 270 venturi...

Jim said most are running 280-290s. I guess 270 is a little smallish? He said he could make anything i needed but i thought I read somewhere 270. Trying to tame this thing a little and get better fuel mileage. Lost a cardinal to running out of gas in the top of the clover...4-1/2 ozs...or maybe it was the "tall" wedge I was using?

Hi Chris,

I have a B40 in an oriental with a 4oz tank. It runs easily for 7-7.5 minutes.
What prop are you using with your B40? Min REALLY likes the 10.5 x 4.5 acp.

-Dan

At least the earlier batches had .305" venturi bores. That's pretty big for a .40, but the muffler outlet was restrictive and balanced it out. Later batches had bigger muffler outlets, but I can't say if the venturi bore was same or not.

If you read Randy's pinned posts at the top of this engine section, you'll come to understand that whether the intake or outlet is restricted or enlarged, both change the pumping ability of the engine system as a whole. It kinda seems to me that a smaller venturi might be easier to deal with than a restricted exhaust, because it should run cooler with a free flowing exhaust. Maybe especially with a low-time engine. 

An easy way to make the 4 oz of fuel last long enough is to add up to 4 oz. of Coleman camp stove fuel per gallon of whatever glow fuel you want to run. Remember also that more nitro, more oil, or more prop load reduces run time, while less oil, less nitro or less prop load increases run time.  Steve 

You could keep the current venturi and place several layers of pantyhose over the opening. Cut them into oversize pieces and hold them on with a rubber "O" ring. You can vary the effective opening size by adding/removing layers.

John

My Brodak 40 will run 4 mins 15 sec every time. I would love to see it run longer on a 4 ounce tank verses tearing apart my Ares. Even if I did open the nose up there is very little room left before hitting the leading edge that's running thru the body. I'm all ears on improving the run time.

An easy way to make the 4 oz of fuel last long enough is to add up to 4 oz. of Coleman camp stove fuel per gallon of whatever glow fuel you want to run.

This works well.

What fuel are you running in this thing?  That may be a clue as to why you seem to be suffering from poor fuel economy compared to other folks.

An easy way to make the 4 oz of fuel last long enough is to add up to 4 oz. of Coleman camp stove fuel per gallon of whatever glow fuel you want to run.  

Any downside side to this ?   Exactly what is the Coleman fuel ?

Ya'll trying to solve things the hard way. 

B40 WILL fly 6 minutes on 3.25oz with the big venturi and and non-restrictive muffler! In the beginning, even after bench break-in, the fuel economy will suck. It will start to improve around flight 25-30 and will get progressively better over the next 30 flights and eventually settle.

To give you an example: I have 4.25oz tank in my VanLoo Chipmunk. When the motor was new, I could not complete pattern. It would cut out right after vertical 8. After about 20-30 flights, I noticed that I was able to do a full pattern but with just a couple of laps to spare. The economy improved so much to the point that I had to start taking fuel out. Eventually, the engine settled on 3.25oz and stayed there for 10 years.


P.S. Tip for beginners: never try to fuel precise amount into an empty tank. Instead fill up the tank completely and measure how much fuel you take out.

Any downside side to this ?   Exactly what is the Coleman fuel ?

Like Brett said, "white gas"...sorta. Kinda blue, as I recall. Said to be more purified than true "White Gas". When "white gas" went away, Coleman started selling their own fuel. You can get a can (a quart or liter?) at K-Mart, etc. Usta be able to get 1 gallon cans, but I can't say if it's still available in gallons. The cans are nice, tho.

Dave Royer says he usually uses some Coleman fuel in his engines, and that starting is better with, than without.  It was Dave that jetted down to the nearby K-Mart and got the Coleman fuel for Mark Scarborough's Magnum XL .53 powered Avenger last October with cool temps and high barometric pressure. Mark used my 1 oz syringe and eyeballed the partial gallon jug of fuel...added two oz for about 2/3 gallon, and got his flights in without any early flameouts. Based on witnessing this, I would be good with using it until the fuel economy improved on a low time engine, or long term if required. At minimum, this is a great trick for when you (or a buddy) needs extra run time to get the pattern completed.  Steve