Is your engine running a stock cam, heads, and pistons? Is it a 4V or 2V engine originally? The 2V version has dished pistons and lower compression - which in turn, does take a bit of the 'snap' out of your acceleration.

Your choice of carb is kind of a mixed bag. Your AVS/2 would hate 7.5 lbs of pressure, and probably blow the needles off the seat. It does have annular boosters, but it's also 650 cfm if I'm not mistaken. The 600 CFM Holley works okay at wide open throttle once you get your RPMs up, but its straight leg boosters are very lazy at low flow.

Your engine is a 289. It does not draw enough CFM to make those carbs work well, with a mostly stock build. Once you get to RPMs, it can start to atomize and draw fuel well, but off idle (especially with an automatic and 2.79 rear gears!) it probably has a wicked bog with those carbs unless you roll into it slowly. More realistically, you probably "need" about 400-450 cfm.

A 500 cfm carb with annular boosters (like the Summit M2008VS) works amazingly well on a 289.

If you are more concerned with peak power, and perhaps have some performance upgrades like heads, intake, headers, you may well need the 600 CFM version to let it breathe on the top end, sacrificing just a little bit of throttle response and power down low.

Lastly, I always question others' ability to set my timing. I'd check the numbers myself, seeing where the timing starts, where it ends, and make sure it's advancing and retarding properly with RPMs.

 

Good morning,
The previous owner stated it was bored .030 over, and was rebuilt around 2011. The motor has the following installed on it. (Limited info on the build from the previous owner)
Eldelbrock AVS 2
Eldelbrock 289 performer intake
unknown cam, lopes a little
Headers to a 3" dual exhaust

Unknown on what else was part of the build, what was originally on the motor.

 

You might want to check the amount of vacuum advance being added at light throttle and, if necessary, adjust it downward a bit.

 

Will do!

 

It sounds like the typical old car with several little issues. Before spending more money on it, I would get a copy of the Ford Shop Manual (FSM) for your year and begin doing a full tuneup. In the process, you will identify parts that are out-of-adjustment (such as vacuum advance) or truly "bad", which is uncommon, and set a baseline for performance and general operation. This should provide enjoyable and reliable driving and leaving little to go wrong.

This is all part of the care and feeding of classics, and part of what you bought into. You can do it yourself for enjoyment and experience, or pay $omeone qualified to do it for you. Your mechanic offhand sounds iffy for being qualified by the results. Find a (any) local car club for mechanic references. IMO, do the basic once-through and go from there.

 

Update: Mustang is running fine now! (Wife is happy)

Mechanic went back through it and found that the harmonic balancer with the timing mark has moved over the years, so the timing was off, but the timing marks were showing correctly. Reset the dwell and timing, fired right up and is running good.
Now onto the Wife's priority list on what to be done next, "Tunes, I need tunes" LOL

 

Well, have heard the phrase "Happy Wife, Happy Life"! Yeah it's true......

 

Now get your balancer rebuilt. Engine should run smoother...and you'll know your accurate timing.

I used Damper Doctor for my 68

 

Going to order one up on Monday!