I can understand the frustration, I have worked on the Model B for many years. I can barely get my own to run anymore, my advice in this day and time is DO NOT let go of one that has been running good. Warpage both inside and out and what Jerry just commented on. Too many gorillas and third world countries (parts and people), are working on them. Keep what you have and check Mike's Carburator for parts and you tube that he has out there. Check valve is where I would check first. I have an on/off valve on my 54 AD and it comes in handy due to it not being started frequently enough. Look around and find a good used carb, the longer it has set the better for you. I do have 5 rebuilt ones but I would not trust their being better than what you already have. This site has all kind of help for your problem, Jerry, Carbking and many more of our friends have touched the subject over the years. Good luck. Oh I do have some NOS horn and bases for most of the B's. Doc.
