390 fe at the dyno, help please

[MaSnaka]

As I have suspected for some time my engine has been under performing. This being confirmed at the dyno tune. Here are some basics...390 fe, standard stroke, reasonable cam, stock iron heads, 750 Holley Street Avenger with vacuum secondaries, 20"x9"x2" oval air cleaner with K&N element, restrictive sidepipes.

The tuner finds I am running very rich, below 10/1 AF the minimum the sensor will pick up. Rear wheel HP at 240, torque at 280. Carb has 72/74 jets respectively. He kept going smaller and smaller on the jets and ends up with 64's primary and secondary and has the secondaries opening in the 3000 rpm range. AF is 14/1, a little wavy but as close as we could get to a flat line through the rpm range. RWHP is up to 270, torque 380 and falls off at 5200rpms. All this with no air filter installed and figuring the air filter would bring us down to 13.5 AF. Well with the air filter installed it went back below 10/1. Now, I have learned something very important. My air filter is actually resting on top of the choke horn thus only about 1/2" of space on 3 sides for air to pass by and into the primaries. Gag me.

Thoughts- 750 carb is too big and should be reduced to 650, that was Holley's suggestion. Are the restrictive side pipes not allowing the 750 to breath properly? Loose the choke horn because I don't have the room for a taller air cleaner. Replace air cleaner with top and side breathing unit. Replace restrictive side pipes.

Plan of attack- Replace restrictive side pipes first and hope I can use the existing carb. Tuner says mufflers/glass packs with 2 1/2" open flow should be plenty. Upgrade the air filter with top and side elements to improve airflow to carb.

Advice- If I still need to reduce the carb, is the 650 Holley 4150 HP double pump with mech. secondaries and no choke horn a good chioce? This is mainly a street car/cruiser but I want it to have some muscle, hopefully with atleast 325 RWHP and good torque. I'll take more but this should keep me happy awhile.

Thanks for any imput.

John