Box Stock

Carb bore

Each casting will be different from one to the next, they are not all the same. Generally the SP hemi carbs without a sediment bowl on them can be made a little bigger before breaking thru the casting. If you are planning on running open or S/a, I would go ahead and switch to a gx390 carb, they are 21mm stock and some can be bored to 23mm-24mm
 
390 carb

W5R said:
Each casting will be different from one to the next, they are not all the same. Generally the SP hemi carbs without a sediment bowl on them can be made a little bigger before breaking thru the casting. If you are planning on running open or S/a, I would go ahead and switch to a gx390 carb, they are 21mm stock and some can be bored to 23mm-24mm
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I have a S/A and I am concerned that the 390 carb with its venture size will slow the airflow.
What is your experience with the 390?
 
Nothing but great results with the 390carb, works well with stock valves, but better with bigger valves. I would run it on methanol if possible
 
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