Originally Posted by Coolball
Hello again hotrodders! I need some help with this carb. It's a street avenger 670 that's been rebuilt fresh and installed. I think there is couple things going but I don't know quite which way to go and would greatly appreciate some direction.
Fresh sbc 350; 9.6:1 compression; 14* initial, 32* all in by 3,000. 4spd manual.
Problem is that when floored from rolling cruise, it's a dog until the secondaries kick in and then it comes alive and will turn the tires off in second gear. I can feel the secondaries open which I know isn't right.
I'm getting ready to change the power valve to an 8.5 from the stock 6.5. It's pulling 17hg vacuum at idle. Jets are at 68 primary and 71 secondary. I've changed the pump cam to blue to get rid of a lean hesitation from idle. I also changed to a 35 squirter which helped a lot.
Last but not least my idle mixture screws are only about 1/2 a turn out from closed which doesn't seem right to me based on the recommended starting point of 1 1/2 turns.
So where am I off at on adjustment?
A lot depends on the cam you are running, what type off heads you have, and what the rear gear ratio is as well as the first gear ratio of the trans. For instance, if you have a 3.08 rear gear and a Muncie M21/22 box, it'll be sluggish off the line, regardless. If you can give us that info along w/the type of intake, exhaust, vehicle weight, how you use it, the fuel you use, etc. Here
is a page you can use as a guide.
If the cam has a fair amount of duration/overlap that gives a rough or choppy idle, 14 degrees may not be enough initial timing. Are you using a vacuum advance? If so is it connected to ported or manifold vacuum? Vortec and other fast burn heads can use 34 degrees total timing just fine, other heads that's not going to be enough for maximum power.
Before changing the PV you need to see what the vacuum is while the vehicle is being driven as you do normally. You may find that a 85 PV will be adding fuel even when you're under not much load- and that's not needed. In most cases, a 65 PV will be about right; rarely is a higher opening point a help as long as the jetting is correct.
To set the idle mixture screws use a vacuum gauge to get the highest vacuum at idle.