The main venturi size is about 29 mm on the 38 Weber, which is very small for a perforamance 250 I6.
Rules for a non turbo car with a Weber are:
max jet oriface size, 1/16 th of the venturi,
min jet oriface size is 1/23rd of the venturi.
Best one to start with is 1/20 th venturi size.
A a full house engine can take 180 micron jets,
the smallest and even the most tame 200 engine can take 125 main jets.
The ideal jet size will most likely be well up from 145, and you just try going up jet sizes untill you get a 13:1 air fuel ratio at wide open throttle.
On a 250, you'll be going upwards on 145's for sure. I'd say start at two 170 jets. This could give you in excess 165 hp if everything was well sorted. Thats 425 cc/min flow. In general terms, there are 5.2 hp for every cc perminute of flow. Two 170 jets would discharge 850 cc's per minute at wide open throttle, or about 165 hp net. If that runs too rich, back off. You've got to carb from the lean side then richen up.
Here is a jet selection graph from RogueS which has the oriface size in micron scale on the bottom (the graph says mm, but it is actually mm times 100, or microns mm scale).
On the left, there is the call size in cubic centimeters per minute (cc/min) scale on the left.
Depending on where you get your jets, they can be labled either way.
The emulsion tubes can stay as they are. These are an aeration tubes, and unless someone gives you a reason to change, leave them alone.
The air correctors go up with jet size.
Another note, which you may consider. Even on little Pinto engines, the DGAS 38 is quite small in the venturis. I'd look at going up to 32 mm venturis by having them flycut.
A stock 350 Holley 2-bbl has 30 mm venturis, and is really only a 125 to 130 hp carb.
A stock 500 Holley 2-bbl has 35mm venturis, but can flow 175 hp on a smaller engine with ease, and on up to 220 hp and still be streetable on bigger six cylinder engines.
The Weber DGAS 38 is a very good carb, but it could take bigger bores than 29 mm on a worked 250, and the jets would go up to 175's and power level would go up as well. You might see more than 170 hp.
