Howdy back RudyD:
For good reliable, stock type performance the stock OEM Carter YF you have is hard to beat. How long has it been since you've rebuilt your stock carb? If it's been more then two years of daily driving it's a good bet that the accelerater pump needs refreshing. And if you're in a climate where the auto choke is regularly activated you can bet that varnish and crud have crept in. Know that your stock '70 200 Carter YF is rated at 187 cfm.
The only thing that would condemn your YF to the recycle been would be if the throttle shaft holes have worn sloppy. That would create a miserable vacuum leak. The holes can be rebushed, but that is not something most home hobbiests can do and is expensive to have done. IF you fall for a "Factory Rebuild", you could get lucky, but most likely you'll have to disassemble, to clean and verify it is put together correctly.
A fairly easy upgrade would be to a Carter RBS. This is the 1 barrel used on 250 engines from 1970 til being replace by a 250 version of the YF, mid decade. The advantage would be an increase in CFM to 215. The RBS may be slightly easier to rebuild, but the same as the YF in being vulnerable to dirt and wear.
The fuel line would have to be reoriented slightly. Both utilize a cable throttle linkage so that should not be a problem. I think the air cleaner mount is the same. Carefully check the carb to carb flange adapter. It orients the carb to the flange. You may need to use the RBS adapter too to correctly orient the carb.
Hope that helps.
Adios, David
