Selecting Carburetor Choke Size

[benlilly]

Hi Guy,

I have found quite a bit of info on selecting carb choke size based on bhp and rpm but the result seems to differ depending on the source of the information.

Would a good basis for selecting choke size for my Dellorto 45's be the peak flow of my head? When you tested it for me you found it peaked at 105CFM @10' depression and 10.4mm lift (results below)?

Ben Lilly 205GTi.pdf

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BL peak flow.jpg (111.23 KiB) Viewed 5683 times

In your 'General Tuning Hints' section of the website you say that a 33mm diameter hole will flow 102 CFM @10' depression. For a larger hole the flow will increase by the ratio of the radius/diameter squared. Based on this, for my choke to flow 105 CFM, I would need:
105/102=1.029
(33^2) x 1.029=1120.581
Sqrt 1120.581=33.475mm choke (round up) 34mm choke

Is this a good way to look at it?

Thanks,

Ben

[Guy Croft]

Sure Ben,

I'd use 34mm or for more power 36mm chokes,

GC

[benlilly]

Ok. Thanks very much.

Ben