Looking at a fantastic refurbished holley 600 cfm..its mechanical secondaries..
Is there issues running a double pumped on a mildly built 300?

 

As long as you educate your foot to operate it, probably not. What usually happens is too aggressively mashing the gas with a resultant bog, stumble, etc.,...and blaming the problem on the carb when the problem is operator error. That is why vacuum secondaries are recommended for street use...they can be adjusted so the carbs will respond to what the engine wants rather than what your foot wants.

 

Understand. I know vacuum secondariesare the more fuel efficient choice too since the engine only uses what it needs. My Edelbrock is a mechanical secondary with the air valve..but upon inspection the carb is pretty much junk. I was mulling over getting a holley 4150 series double pumper..cuz the only mechanical secondaries they have are the double pumpers. They offer them in both square and spreadbore. The spreadbore would probably act more like a q jet and have better throttle response but I'm not sureif its wise to adapt a square bore intake to a spreadbore carb..so I think ill look towards the square

 

Holley site info, points to the 600 CFM for what you are doing:

http://www.holley.com/data/TechServi...Carburetor.pdf

Vacuum secondaries would probably be easier to live with.

 

Exactly. They have a 600 cfm dp I'm lookin at. I just bring all this up cuz we as the 300 guys tend to stick towards the 350-500 range if we convert to 4 bbl. And even so we like to stick to vacuum secondaries. I don't mind goin to 600 and mechanical secondaries means I get to control it and less parts to leak (vacuum diaphragm). So..that's why I was curious as to see what some opinions are to run a 600 dp

 

A dp could probably be made to work well on a relatively small, low-rpm engine like a 300 but will require a lot more tuning than a vacuum secondary carb. Tuning either on a dyno or a few hours logging data with a wideband O2 sensor under all driving conditions.

Does your vehicle have an auto or manual transmission? Mechanical secondaries usually work better with a manual tranny (for street use, strip is another story...) than with an auto.

You say you've got an Edelbrock that's junk, but it's amazing what a $20 bucket of carb dip and a $35 rebuild kit will do for a "junk" carb. Edelbrocks have a great reputation as a slap-it-on-and-drive-it carb. I'd spend the fifty or so bucks to rebuild that Edelbrock first, see how it drives, and think about spending $300+ for a new carb later.

 

Appreciate the advice Baron. I have a manual tranny. As for "junk" its missing parts and some of the linkages are frozen. I won't buy a carb new. I know it sounds weird but I can get it cheaper and put a kit in it myself cheaper than a new one. I know I run the risk of missing parts and any adjustments any po has done

 

For about $100 you can buy a nice Autolite 4100, 1.08 venturi, 480 cfm, on ebay. Get one for a 352 and you'll be happy. Annular fuel discharge will get you great mpg, with plenty of performance.

 

I looked..nothing below 300 haha its good. I'm going to keep my options open. I would LIKE a mech secondary carb..but I guess its not necessary. I also look towards manual choke just cuz I want my choke pull **** to still have a use lol

 

I wish there were smaller mech secondary carbs. I say this..cuz of contemplation. I know the bigger carb I run..ill have less low end. Wish someone had a 500 cfm mechanical secondary haha. Just feel like is be losing bottomed end with a 600..at least what I've been told.

 

There is a 450 cfm Holley spread bore mechanical secondary carb...model 4350 sometimes called an "Economizer". I originally had one on my engine. But it was basically not much adjustable. The main jets could be changed (Weber), the idle mix and speed adjusted and that was it. A very economical running carb but a definite stumble or bog at tip-in especially at lower engine speeds. The accelerator pump was not adjustable so as to cover the lean hole created when opening the throttle.

 

Why not try a Edelbrock 1404 , 500 cfm ?

 

What made you decide on a mechanical secondary carb? It's really not a great set-up in a big heavy truck with a low-revving engine like the 300.

I've got one on my Mustang (331 SBF, 5-speed, 3.73 rear gears) and it works well...but the vehicle is at least 1,000 pounds lighter than your truck and has a much lower effective gear ratio. And it gets wound out to 6,000+ rpm.

 

Harte..yes I've heard of it. Didn't know it was mechanical. I've seen em around but they're pretty expensive..I'm rethinking I should just stick to a vacuum secondary. I have a manual transmission and didn't want a loss of performance with the vacuum secondary carbs.
Hotstuff...I have an Edelbrock 600 cfm now that's in need of some tlc. I'm going to go tinker with it this weekend..maybe put a kit in it.
I found a holley street avenger 570 cfm vacuum secondary local for about 200. Guy ran it for 3 months and took it off..been sitting in a garage for a couple months. Heard these carbs were made for low end power and making strong high end power. And its 570!

 

I think its just the throttle response. I would like to run a 500+ cfm carb..but my reading has led me to believe that bigger carbs will less to less throttle responsiveness and less low end power..so I THOUGHT possibly a mech secondary would be ok and combat the throttle response.
I've also been reading about Holleys adjustable vacuum and it intrigues me. I've also been looking at the thunder series edelbrocks due to their adjustable air valve but (and again research) that the adjustable vacuum yields more than that of the adjustable air valve in edelbrocks. Hence why I've been looking at a 570 cfm street avenger.