From what I just found on another forum (Google Ford 2100 jet sizing) it appears that you set yourself up for failure.  Not hard to do, just don't ask how I know. 

By going to the smaller venturi carb you increased the velocity of air at any throttle position, including idle.  So, there is more vacuum on the main jet and it will feed fuel even at idle.  Then you went to a size 40 from a size 50 main jet and according to what I can find, the Ford jet size is like drill sizing which means the 40 is WAY BIGGER than the 50.   Add to that and the fact that one side of the pot has a blocked idle air passage which could make it a lot richer and you have a very rich set up.

So while the old pot was ancient it apparently worked well so you did a BB.  You fixed something that wasn't broke, so now it is.  

Find and fix the idle circuit problem.  Then check the jets...I'm betting the old ones are smaller...and put the smaller ones in the new pot. 

Check this thread.  Sound like he's having the same issue as you.

http://forums.vintage-mustang.com/vintage-mustang-forum/634370-carb-jetting-rich-lean.html

And what's said here about re-drilling jets is true...I've done it many times when tuning VW's.

BB
 

Last edited by Bullet Bob (3/31/2017 7:57 AM)

TimC wrote:

And if the gas in the tank has been sitting for a couple of years, its gonna be stinky too.....

....especially so with today's ethanol gas!
 

Bullet Bob wrote:

From what I just found on another forum (Google Ford 2100 jet sizing) it appears that you set yourself up for failure.  Not hard to do, just don't ask how I know. 

By going to the smaller venturi carb you increased the velocity of air at any throttle position, including idle.  So, there is more vacuum on the main jet and it will feed fuel even at idle.  Then you went to a size 40 from a size 50 main jet and according to what I can find, the Ford jet size is like drill sizing which means the 40 is WAY BIGGER than the 50.   Add to that and the fact that one side of the pot has a blocked idle air passage which could make it a lot richer and you have a very rich set up.

So while the old pot was ancient it apparently worked well so you did a BB.  You fixed something that wasn't broke, so now it is.  

Find and fix the idle circuit problem.  Then check the jets...I'm betting the old ones are smaller...and put the smaller ones in the new pot. 

Check this thread.  Sound like he's having the same issue as you.

http://forums.vintage-mustang.com/vintage-mustang-forum/634370-carb-jetting-rich-lean.html

And what's said here about re-drilling jets is true...I've done it many times when tuning VW's.

BB
 

I changed the jets to the 50's.  World of difference.  Vacuum is at 16 now instead of 13. My ignorance in assuming bigger number means bigger hole cost me lots o' frustration.  The carb is off a '64 full size Ford and I don't know which model or engine, but the 43 jets came with it when I bought it. The rebuilder probably set it up for use on whatever a full size Ford had in those days. I think with 245 cfm it was maybe a 260, which is why I thought it would be a better match for my 250.  Anyway, I still have a blocked idle circuit somewhere even though I cleaned and found blocked holes on the non-working side. The idle screw has no effect on anything on that side, still. Any suggestions on how to clean the idle circuit or should I just tear it down and give it a good soaking in carb cleaner and re-gasket the poor thing? It is still running rich and I know I have some work to do to find the optimal jet size but things are much better today!

Thanks! 

I'd like to see something in print about Autolite jet sizes being smaller as the jet size number increases.  I find that hard to believe.  If you look at the 4100 jet sizes for an A code 289, then look at them for a 289 hypo, the hypo jet numbers are larger.

And, as long as I'm windbagging....
Don't forget the pie, ah, I mean don't forget pi.  It's easy to think, " well, I'm only changing the jet size by .005 but you need to remember what effect that has on the area of the hole.  Muzz went from a 50 to a 40 jet and if those are close to drill sizes he actually went from a .070 to a .098 jet.  The area, though, went from .00385 sq. in. to .00754 sq. in....nearly double.  I learned this the hard way when my old 4-Banger racer buddy 'splained the facts to me.  A couple of thousandths can make a huge difference in jets.

Okay, I'll zip it.

BB

Last edited by Bullet Bob (3/31/2017 9:19 PM)

Leaking power valve can also cause really rich idle..

The jets don't flow at idle, do they?

Clean it. I prefer spray carb cleaner vs soaking. Wear safety glasses and use it to blow through all passages. Put a kit in it and I bet it will work like new.

On that clogged Idle circuit. Quick fix that sometimes works, is to get it running with the breather off, rev it up, then with it revved close the choke and hold it a few seconds, usually will suck minor clogs out pretty quick. 

Last edited by bulletbirdman (4/02/2017 11:05 PM)