Motorcraft carb ???

Do any of you fellow jeepers know for sure if a Motorcraft 2100 with the 1.21 venture size will work on a 304. I'm trying to sell the one I have in the garage and there is an interested party here, but thinks it's too big. I ran this for a number of years on my 258.

thanks

High5

 

the 1972 FSM shows the stock main venturi size 1-5/64" for 1972 304-360 V8s

 

That's 1.08" which is the usual size recommended for the 258. Your potential customer is right, in that the 1.21" venturi is larger than what's recommended for that application. If the venturi is too large, the vacuum created by the air flow at low speed is too low to provide good atomization of the fuel. A larger carburetor will have better "volumetric efficiency" at high RPM though, because the air pressure difference between the fuel charge in the cylinder and the atmosphere will be less. This means a larger fuel charge in the cylinder and more power.

Usually if the carburetor is too large for the application, you need to run a richer mixture than would be ideal, becasue of the poor atomization at low RPM. This, in general, when combined with the lower volumetric efficiency, is why a smaller carburetor usually provides better fuel economy than a larger carburetor. That, and the larger carb encourages spirited driving. However, the Motorcraft carburetor has a very effective "booster" venturi that may be sufficiently effective to allow running a 1.21" carb on a 258. There's no rule that says the 1.21" carb won't work on the 258... I expect that those who tried them first chose the 1.08" carb according to some well-known rules of thumb about CFM and engine size. Either the 1.21" or 1.08" carburetor could be best under certain circumstances.

That's the story - maybe this is enough info to convince your buyer to try it.

 

Yes - I missed that it's for a 304. I ran a 500CFM Holley 2V on my 304 for a while, and that's about the same size as the 1.21" MC2100. It gave an obvious boost in power, and ran great on the street. I went back to the original MC becasue the Holley performed poorly on hills.

Should work fine, although it will give more power and likely less economy than the original carb.

 

Thanks guys for the replys. This is a carb that has run on a 258, but the buyer is wanting to put it on a 304. Now I just need to figure out what shipping will be to Nova Scotia

Thanks again,

High5