3310 - Is it too much carb for sure on a mild 305?

[Randysmojo]

I know it seems just a bit ignorant to put a 750 cfm carb on a 305 Chevy even if it's vacuum secondary, but I got the carb for such a good deal, I couldn't pass it up. I was hoping I could down size the jets, put a stiffer secondary spring in it, and use a small accelerator pump nozzle and tune it to work. Has anyone successfully made this happen, or am I just chasing my tail? I tried #65 jets, #50, and I will be trying some brand new #55 this afternoon if they will ever get here. Even tried #40, but it wouldn't even run with those. It idles fine with the 65s and 50s, but falls on it's face when I try to gas it some. Adjusted the accelerator pump proper, and it isn't much better. I just set the timing, but figure I should make sure it is still on. Just looking to see if anyone knows what the magic combo is, or if I should just sell it and get a 1850.

[Gaz64]

For a stock engine, you would be better off with a 600, so 1850, etc.
I've run 750 DPs on modified 302-308 engines with good success.
Please explain your numbering above, 65 is your new main jets, but what is 55, 50 & 40? Gary

[Randysmojo]

65 was the first set of jets I had in it. I tried 40s and 50s and I just put 55s in it, but haven't got to start it because I have to pick up my son, so I will try it when I get back home. I figured it was stumbling because the 65s were too big for it. Right now it has a mild cam and performer EPS intake. Am I going the wrong way with it?

[Gaz64]

40 main jets? You know Holley carbs aren't jetted in steps of 5 (.05 mm) like a Weber.
Be lucky if it would respond to the main circuit at all with such tiny mains. You really need a 550 - 600 VS.
The largest issue you have is the venturi has poor booster signal, since is on the large size for the engine.
The most important part of selecting carb components is venturi sizing. Gary

[Randysmojo]

That's what I was afraid of. I got the carb for $40 and rebuilt it. I want to go to a larger engine in a couple of months so hoped I could make the 750 work here for now, so I can use it on the other engine. Might just have to sell it and get a 600, or find someone that will trade me.

[Randysmojo]

This is a video of what it's doing: https://youtu.be/mKRSImEEjoE. Same thing with the 55 jets and the 65 jets. Idles fine.

[Gaz64]

Yes, that's bad and undriveable. Are the float levels correct?
And I could bet you could go rich on the mains at 80s, and it would still do this.
Keep it if you want to for the future, but this engine needs a smaller carb.
If you want to stay with a Holley, a 650 spread-bore 4175, a 4010 600 VS, a 550 as above, etc., would be better choices. Gary

[Randysmojo]

I found someone 10 minutes from my house that will trade me straight over for a working 1850!

[Gaz64]

Sounds good, might here back from you once you've done the swap. Gary

[Randysmojo]

Yeah. It needs a new needle & seat for the primary float, but looks good otherwise. New parts on the way!