What's it Flow?

[akilbar]

I am using a flow meter with the tubes and balls ( not the blood pressure cuff style). I am setting up a 21 rigger with CMB 21 LS black case. I am putting one of Andy's fine needles in it. I want to base set it at the shop before going to the pond. I have it se now so the radio will take it from about 1.8 up to 3.0. Is that a good range to start with??

Thanks.

 

[bzubee]

I'd go from 2.5 to 3.5 or higher if possible. I haven't tested on a CMB but Nova Rossi setting is right around 3 or 3.2 most of the time.

 

[Mike Hughes]

It would better to set it by ear. All flow meter will read differently then the other. Depends on the length of tube and breather size. Plus all set ups are different, pipe, carb, motor, boat, prop all come into play. Start out on the rich side. Just fire it up on the bench pull the trigger to full. As you do you will notice that it will bog down and take a while to wrap up. Lean it up and as soon as the bogging stops and you start to get good throttle response you are there. Go to the pond and test.

Mike

 

[akilbar]

Sounds about right Mike.

A related question, when you flow test, you have the fuel line hooked to the carb and the throttle open, right??

My MAC 45 in an SG flows about 3.3 to 3.4 perfect. I am guessing in the mid low 2 range for this.

 

[bzubee]

Yes carb has to open unless you are just flowing the remote needle. You could also run the boat with a remote maual needle 1st take a reading on that and then set your remote needle according to your readings.

 

[John Knight]

I was provided some time ago with some generally accepted ranges of flow for engine sizes. They are:

Engine Flow

3.5cc 2.5 - 4.2

7.5cc 3.2 - 4.8

11cc 5.2 - 6.5

13cc 5.5 - 6.9

15cc 6.5 - 8.0

Mike is right that there are too many factors that influence an exact setting. But I can tell you that the ranges noted above are fairly close. I use them to get close and then use Mike's method to nail it down. That was the way I did it before I got the flowmeter. The closer the engine is to stock the lower the number will generally be. The more mods made = more fuel and will be towards the higher number. Intention is to get it relatively close. Keeping a good set of log books for past setting will help greatly. I have a 90 CMB engine that flows about 8.2 often. My others are normally in the range noted above. No absolutes as it is an inexact science.

 

[Mike Stewart]

Flow..... The one in my kitchen is Linoleum.

 

[Mike Hughes]

It is better to error on the high side. Seen to many times when you fire it up and goes straight to 30-40 thousand rpm. Not very good on your motor with no load. Tends to do damage.

Mike