Dazed and Confused
Join Date: May 2012
Location: Upstate New York
Re: Best jet size?
Well, on a stock unit, you're usually looking at around 50 on the primaries and close to 60 on the secondaries. A 4150 is the carburetor model, not the size. For a high performance 289, it shouldn't exceed 600 unless it has some really radical mods. You're probably looking at 50-52 for the primaries, and 60-62 on the secondaries. Best to get a kit (they're reasonably cheap) and start there, run it. If you're lean on cruise, step up 2 or more sizes (one size doesn't really affect you much), rich step down. Then do the same with hard acceleration. You'll notice the difference with response, when you're close, improved response will plane out, go too far and it will start to go sluggish. if it gets sluggish, back off about 3 sizes. That's how we used to do it before the days of carb tuning shops. If you;re really a stickler, there are shops around that will monitor air intake and exhaust to get peak performance a lot quicker and much more accurate with no guess work, but they will cost you.
Ever notice that there's so many high performance parts available for GM products?
Did you ever think that maybe they NEED them?