Just for reference the 57 Ford shop manual shows for the 312 holley 4150 the main jets are 55 and the secondary jets are 48 with an 8.5 power valve. I think ? I am running 55 or 57 main jets in my 4160 and I ran 63/65 in my 289 hipo in a 66 shelby  with a 650 double pumper so the 66 should be too big. Pete

Hmmm never thought about altitude (shows you how much I know :blush, but where I live, close to Toronto we are about 270' above sea level, not exactly Colorado!  Also, never even thought to check the secondary jets! I'll have to do that tonight. Thanks for the info.

Rob

I love the smell of burning rubber in the morning!

What is the altitude where you live?  This will affect things at least by a couple of jet sizes. 

I have never ran this particular carb on my y, but from the others I have I would speculate that #66's are probably a bit big for the primary side.  Are the jets in the primary the same as secondary?  For a stock y, with that large a carb, I would be willing to bet that a 55-58 primary & 64-68 secondary would be adequate.

Alot of the others on this site have used Holleys with a great deal of luck.. I like to tinker with carbs on my schedule, so I do not use Holley..  I personally think Murphy & Holley are cousins!

Hey I'm finally catching up on my "honey do list" and can actually find time to work on my car!  I know there was a previous post on this but I just want opinions. I am finally rebuilding my spare carb and I don't want to take apart the one on my car until I confirm that this one works well. That being said, I have NO Idea what jets are in the carb that I've been using for the last 5 years! Yeh I know, pretty basic, but it has run so well up to this point I didn't want to mess it up! Now my spare carb (Holley 4150 / 600 CFM) has a ste of #66 jets. Do you think this will work ok with a stock motor / cam or should I downsize? I just want to start with a good base, and I understand I might have to do a little trial & error, before I get it right? So let me know if you think I am off the mark to begin with. Any feed back is appreciated. Thanks.

Rob

I love the smell of burning rubber in the morning!