The reason I think too much carb hurts driveability is intake air velocity. Carbs work on pressure differential. Bigger carb(Venturi), less velocity, less emulsifying and atomization of A/F. Lost efficiency.
Ps. don't forget about your ignition system.
Will

 

Jason,

Thanks for the update. I will contact you this evening.

 

Played around with the air/fuel mixture screw on the edelbrock today. Runs a little better, adjusted the accelerator pump to the leanest position, and received the air/fuel ratio kit today from summit. I'll install that hopefully by the weekend, and see where I'm at... To be continued...

 

For you guys running the air/fuel monitors how do the plugs end up looking at the ideal ratio? Are they leaner looking in appearance than you would have otherwise run, without knowing for sure?

 

In my case they look the same as before I installed the gauge. Couple problems with reading plugs, today's fuel has made reading more difficult as they are very similar in color even when somewhat rich or lean. If you are trying to read the plugs for cruising down the highway, you really need to pull to the side of the road and read the plugs, I have done this a few times and getting plugs out of a hot engine is no fun. If like me you have to drive slow returning to your house by the time you get there the plugs have changed and with the vagueness of the color change there was not much info I could discern.

The only way I "knew" the engine was rich was just a feeling by the sluggishness of the throttle.

 

Interesting, I've wanted a wideband for a while and read that often people are amazed at how far out things were once they installed one.

 

Remember that those screws only impact things at low idle. The more RPMs you turn (even stepped up on the cold idle cam) the less impact those screws have. This isn't as true (still true . . . but not as much) on older carbs. EPA forced everyone to make those screws less effective. They used to put anti-tamper caps on the screws. They popped right off with a screw driver, just had to make sure that you didn't bend the brass screws. So EPA limited the size of the flow. About the only thing that they are good for is to smooth out the idle. Even then you can mask an ignition or valve problem.

Here is an "old school" chart that should help you. You need a vacuum gauge but they are cheap at most auto parts stores.

 

That's what i told the guy at the auto parts store. He was adamant about being correct

 

Here is a video by Jegs that may help.

 

Have to agree with the majority, 750 cfm is too big for a 350 ci motor, unless it's on a NASCAR motor. Cam specs would help. That's the 2nd most common problem building a performance motor. Do LOTS and LOTS of research, and read every automotive article you can. Best of luck, lots of good folks on this site willing to help.

 

- Duration: Intake 262/Exhaust 270
- Duration @ .050" Lift: Intake 218/Exhaust 224J

 

Albuq,
I'm wiring my MTX-L right now, where did you run the red power wire? "isolated 12V switched power source".

 

I found a yellow/black wire that is an accessory wire. got the gauge wired and sensor is calibrated. now just need to go get new exhaust gasket. finally get to see if i'm running rich/lean.......

 

Carburetor jets are marked in motor craft auto lite carbs numbered. What does the numbers mean? I have a 55 jet in mine and was told I can run a 62 or 64 jet? The engine is a 1973 390 in a F-250 4 speed manual. My carb is a stock Motorcraft carb 2 barrel. It had #55 jets in it I tried #64 jets and seemed to rich so backed off to #62 jets What would be correct? Oh and when I rebuilt this engine I installed a RV cam. Would that cause it to want more Fuel?

 

Proof is in the pudding,at idle, in the 12's, when I stomp on it, I'm in the 10's and 11's