Jim, you sound like you're on the ball ...I concur with your statements.
209.....check your jets and accelerator squirter size. As you read on maybe some of it will make sense. If you have a 2 inch exhaust, the potential for horsepower is already gone.
I spent a week jetting the carb....good thing I'm retired. I raced bikes for 30+ years and jetting is jetting. If you know what to feel for, a Holly is a very easy carb to dial in.
The Avenger came on the Roush with 70 pri. and 73 sec. jets, and this was the carb on the engine from Roush. What Roush internet ads don't make clear is that they CAN have 550 HP if you opt for the single plane manifold and 750 Double Pumper. Torque and HP starts at like around 3500 rpm rather than down lower with the dual plane and Holly Avenger 770 or Double Pumper. I think the avenger is what they come with now instead of the earlier Double Pumpers. Not positive on that…
Before I go further, I have to say that a Roush engine has only one part made by Roush that I can find....the spark plug wires! The block and lower end is all "Dart", heads are "AFR", manifold is "Edelbrock, carb "Holly" Ignition "MSD” etc. Smedding builds the exact same motor with the addition of a Quick fuel carb and advertizes 560 HP for $2500 less. It says Smedding on the valve covers. I didn’t do enough research when I bought the Roush or I might have gone with the Smedding.
I've seen numerous 427R motors and they have all been between 520 and 535 HP with the Avenger. I've seen 565 out of one Roush with a single plane and a Double Pumper. I should note I used to go up to the installers shop a lot, and he had these motors all over the place waiting for installation. SR motors with the the Avenger are advertized at 525HP but realistically put out around 510 or 515 HP.
I didn't do any jetting until I replaced the mufflers with 3 inch up from the factory Superformance 2 inch. Crap...my Harley has 2 inch pipes and that's just for 1 cyl. I did a whole other thread on pipes and the whole jetting thing. Lots of good comments and arguments. Go to the search box and type in "Superformance Exhaust"...it's about 10 down from the top.
Anywho...I don't know who got hold of my Avenger (Roush or the installer) and dropped the jets from stock (72-75) to (70-73). It ran very well but had a slight stumble right off idle. It was nothing to write home about, but irritating none the less. It pisses me off that someone messed with the stock jetting because it wound up being the best combination!
After a week of jetting up to very fat then down until I started getting a lean pop, I ended up with the stock jetting (72-75) up from two sizes on the pri. and sec. from what it was. I've been to Tahoe climbing to 7000 feet, to the Calif. coast and it runs perfect up to about 3000 ft. and then gets fatter as you climb higher. But, we just did the Snakes to the Lake for three days in Tahoe and it performed perfectly fine with a little HP loss which is to be expected.
One addl. change I did make was a switch to a 40 accelerator pump squirter from a smaller 37. I will say that when I say it runs perfect It really does not have a sputter, pop, off idle acceleration ....nada!
Oh, I forgot to mention that part of the HP gain with a 750 Double Pumper is the lack of a choke horn that’s a little restrictive on the top of the carb.
