Would I be able to use the plate and rod off the one I have and put it on the throttle body you have?
Matt, I think it may be possible to swap your throttle rod and mechanism from your body to the one I have, but you'd have to use the throttle plate that exists in the 1-788 piece I have. What I don't know, and perhaps Jon H (carbking) can confirm or not, is if the throttle plate mounting holes on the 2 shafts are spaced the same??? Yes the throttle plate screws are staked, but Jon (carbking) or Jon G can explain how to properly remove and replace those. Jon G did say he could help with the conversion if we send him what we have.
On your question of where to buy a YF2100S already rebuilt, there are a few vendors/suppliers that seem to be offering them on the web. Some just offer a rebuild service for your core, which doesn't help with the mismatched parts.
The possibility that what ever a rebuilder has to sell may be a franken-carb is pretty high too. Just the nature of the beast. Just my $.02 worth, but find one that you can confirm has all the correct parts and ID numbers (something like the one I linked to in eBay above) and either get a correct rebuild kit from "carbking" to rebuild it yourself or send it to a trusted rebuilder.
