Turn the carb upside down and take a look at the transition slots in the primary side.  You should only be able to see a very small opening below the throttle blades.  An opening about as long as the slot is wide.  If you have more than that showing, you need to lower the curb idle speed setting on the primaries, and increase the idle setting for the secondaries.  The screw for that is only accessible from the bottom of the carb.  This may also help your rich idle/exhaust fumes issues as well.

Be sure the accelerator pump driver is fairly tight, so the pump begins the shot as soon as the throttle moves.   If you still have issues, a slightly larger squirter may be in order.

You can also change the plastic pump cam out for a red one.  It has a taller lobe and comes in quicker than the ones they supply on the carbs.

Have you done ANYTHING to the timing?  Cammed-up engines want/need ALOT of initial advance. Will clean up the idle and stop/slow down that rich burn smell. And make it go like  crazy!!
6sally6

A good rule of thumb is TOTAL advance(initial and mechanical) should be about 36* all in by 2000 rpm or so. Trick heads sometimes don't need that much advance.....it just depends on your situation.
Here's the part to think about when a "med/heavy cam" is used. Set the initial timing about 20*! You need a good starter/mini starter to spin it over when hot.
What is the specs on your camshaft? duration@050...LSA... lift? Compression ratio too.
In order to get that much timing in by 2000rpm you will need a set of light weight advance springs(Summit/Mr. Gasket/etc.)  May need to make a bushing to go in the distrib to LIMIT the timing ABOVE 2000rpm. You don't want 36*@2000 and 56*@ 3200! Know what I mean? Good tutorials on the net about modifying duraspark distribs.
After this mod..........it will be "getting-away-from-you" again in the first 3 gears!!
I think it one of the best and least expensive mods a person can do on their Mustang.
6sal6

Thanks sally, I will post the Cam specs as soon I retrieve them! 

Jeremy that's the first I've heard of that, so I appreciate the sound advice.  The tip in hesitation did not exhist prior to jet change.  The only other variable I changed was installing the 1" spacer.  Timing and from what I know, the pumps and idle screws were not touched. 

Would smaller jetting cause a tip in hesitation?  If the answer to this is yes, then it must be the culprit, no?

I'd like to start just by saying that I"m not a holley guru..yet lol, however for days upon days i've been reading and tuning and have gained some serious experience.

I do have a couple of holley guru friends, and I was told to get rid of my holley bog issue be sure my mixture screws are set right and that my primary jetting is correct first before I move onto other systems

Logically speaking the problem didn't occur until you performed the jet change, so this also tells me that imo you should re examin your primary jetting and look elsewhere for your rich condition.

There are a lot of different systems on the carb other than jetting that can cause rich conditions...blown or incorrect power valve, even secondaries if the spring is weak or they're opening too early, etc...

I personally am running a 670 street avenger on a mild 5.0 putting out maybe 325 flywheel hp,...probably upwards of 75 or more hp less than what I'd think you make with your motor.  I recently did the vacuum/cruise trick and bumped from a 65 jet to 68 jets on the primary side, and truthefully I think I can go up maybe to 69's,....so it's a guess, but 71's on a 750 carb sound a little small to me.

Check out youtube, both holley and summit racing have some great videos, and they go over the primary jetting systems and how to do the drive testing to find out what works best.

i'm not too familiar with the double pumper, but i've heard the same thing, it's kind of an all or nothing thing with the secondaries...you get gas when you hit it...nice thing about a vacuum secondary carb is that it's operated off vacuum, so you don't get 100% secondaries all the time, you get more or less what your motor asks for, this is how people can run oversize carbs on their engines that don't need it and be fine.

Last edited by jeremy (5/17/2013 9:42 PM)