2100 Carburetor

Hi all, I have a problem I hope somebody here can help with. I have a carburetor that is giving me fits! I have a 72 Ford 302 motor (in a 65 Comet) set up with a Motorcraft 2100. The venturies say 289 on them, and the body is 1.14. This motor had a 1 1/4 exhaust cross over into a single 1 1/2 exhaust. I took that off and installed dual 2 1/4 exhaust into Dyna Flo mufflers. This motor is brand new (rebuilt 900 miles ago) is stock except for Pertronix Ignitor II ignition, and their Flame Thrower coil. The problem is that the motor is running lean, and getting hot. I put a kit in the carb, but it didn't help. The jets were #47, I upgraded them to #49 just because I had them but it didn't make much of a difference. I put a new   vacuum gauge on the PCV valve port on the carb spacer. At an idle either hot or cold the gauge is showing 19-20 inches of vacuum. So I don't think anything is changing. My question is. Because the engine is breathing easier now. Should I up-size the jets, and if so how big of a change should I make?  

Yes, opening up the exhaust will lean out the engine.  As far as what and how far - have no idea.  If it was a Holley, I'd tell you to try 6~10% more in the mains which is 2-3 jet sizes (Holley about 3% fuel per jet change) but Holley parts do not fit a 2100 or 4100.  I don't know if anyone knows the approximate fuel change between jet sizes in a 2100.  I found these people:
http://www.carburetion.com/ford2v.htm for jets
but at $10 a pop, you'll be out a few dollars experimenting.  

Are you sure it's lean - you cannot read plugs with modern unleaded fuel and higher energy ignition parts.  The plugs stay clean, typically, and don't color much.  Is the carb set correctly - float level in particular?  Overheating can be caused by several things.  What timing curve is in the engine?  

More here:
http://www.hotrodders.com/forum/motorcraft-2100-carburetor-38384.html  
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

Beg to differ there Falcon. Putting on headers will normally mean you can reduce main jet size because there is less dilution by exhaust gas of the incoming charge. Exhaust gas is considered inert and so its harder for the oxygen molecules to find a fuel molecule when there is residual exhaust gas in the cylinder. When you make exhaust more efficient you will have an engine that runs rich and will generally need a jet size smaller. Your 1.14 venturi size is good for a small block and corresponds to the size Ford used after about 68 on for small blocks. I have used main jets from 47 to 49 with no problems. What is causing you to think that your running lean ??  

When you improve air flow through the engine, you typically need to add more fuel.  Improved scavenging tends to lean out the mix that lands in the chamber.  On a typicaly List 1850, they come fat enough out of the box that there may not need to be a change except on the secondary metering plate for best top end power.  On carbs like the Edelbrock/Carter that have some finer primary fuel control, you will usually go "one stage rich" of the calibration.  Not a universal rule, but typical of better breathing.  
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.

Not really,,, improved flow better cleans out the exhaust gas left over in the chamber. All cars are calibrated rich because the exhaust gas left in the chamber(by backpressure in the exhaust) tends to dilute the incoming mix, much like egr(exhaust gas recirculation) would. The perfect metering would be stoichiemetric ratio(14.7 to 1) which would be the pefect air/fuel ratio but excess exhaust gas means that you have to go rich so that those molecules find one another. Carbs meter at a set rate ,,,say 13:1 or whatever you set by jetting. It has to be richer then stoichiemetric because all the air doesnt meet up with all the gas. If you run too lean then you get excess oxygen coming out of the chamber,,, not a good thing. Thats why lean engines run hot and rich ones run cool.
What you may be reffering to is a performance engine with long duration cams and a lot of overlap. Typically changing a cam to a profile with more overlap will cause leanness not because the engine isnt breathing well but because the long overlap causes mixing of the incoming charge with burned exhaust gasses, thus causing a lean condition because burned exhaust gasses are essentially inert and interfere with combustion. In that case you have to richen your carb to compensate. However, with no cam changes and simply better breathing on the exhaust side, the carb that had been delivering a mixture at one set ratio will continue to deliver at that ratio and can be leaned out because there is less dilution of the charge in the combustion chamber.  

Sorry mechanical guy I agree with falcon 67 I went on holidays in my 71 falcon while I was away I got a new exhust system put on ( twin system) it made a big difference to the performance but by the time I got home 2,000 killometers I had a burnt out exhust valve, cause not enough fuel I think you are trying to get to technical  
69 mustang grande  600 hp 357 clevo
owner building
steady progress

Its a free world guys, believe whatever you like, and the advice is free too. In my experience as a Ford calibration and development engineer I found a lot of lore that just wasnt true. Things happen for a reason, but it isnt always what it looks like on the face.  

I have noted over the years playing with Fords,sometyimes you can miss the simple things. If the sock on the old fuel sender is gummed up, you will have a lean condition. If the fuel line is kinked, or the filter is plugged up. or a tiny hole in the fuel line, you can get a lean condition. Further investigation is in order. TO>>>> mechanicalguy and falcon67..have either of you guys used one of those air fuel ratio meters to check out a system??? My nephew put on on his chevy, and it fluctuated too much for me to figure out. With the old points, you could read a plug purty easy, but with electronic ignition, and this new gas I really wonder about the old method of reading plugs. I had to put a new valve in a 2002 Tore-ass because the fuel filter plugged up, and it had a massive vacuum leak. The spark plug was angled towards the exhaust valve, and it burned the valve like a torch had been took to it. To be honest, I don't know witch of you are right, but I was always TOLD that if you put on headers, you had to richen up the carb. Its been so long since I got to play with a carb, I've almost forgot how, and I have a 3 Duce set up to put on my old ford, I know I'm gonna have to ask for help..