Tuning my single turbo 401 with a CSU blow thru 4150 holly HP. my idle a/f is 13.8 at 1000prms, cannot control idle with adjustment screw. Tipping into it i am around 12-12.5 a/f from 1000-2500 and going wot or really hammering down i drop to 9.8 and settle in at 10.4 a/f . should i just drop down two jet sizes in the rear and start from their? Engine is cooling now so i can take a look at the plugs and will post later on the findings. timing is locked at 34**
I would send kevin at csu an email but your suggestion is on the right track. What is your target a/f?
First call Kevin. My bet is he will tell you to up the idle air bleeds a little and drop some jet size. That's what Zach at QuickFuel told me. And that won't do &#!t. Next read my thread http://www.v8buick.com/showthread.php?239017-Blow-through-carb-thread&highlight=sailbrd and let's add your info to that thread. Get all of your baseline info on the carb and post. I would really like to see more on what CSU does. Wide open throttle is no big thing on a Holley. Just start dropping jet sizes. Getting the whole curve correct is a different story. You are not bad on idle idle AFR's but you should be able to have better control on idle.
I don't know crap about the carb's but for the boost a 12.0 AFR is a safe ratio until you start getting above 20psi of boost, then you'll want some real expert tuning advice at that point. Below 10.0 AFR is drowing the engine in fuel.
from what I have read changing jet sizes is not the right way to change wot a/f ratio. my target is 12-12.5 at 7 psi. Kevin does use a different style pv with is a brpv from what I have read and I believe fine tuning of the air bleeds and the power valve will be the right thing to do. I will not be touching it until I get a hold of him but thinking of hitting it with more boost and see what happens. I am at 3-5 right now and looking at 7-8 psi wastegate spring on my kitchen counter. he did build the carb for 7-8 pounds so I might do that. I also am at 7psi fuel pressure and thinking of going back to 5.5 psi
I would go to the boost setting I wanted and tune from there. Just be sure to back off if the air fuel ratio goes too far out of whack. I hear of a lot of guys waisting time with carb mods and then have to re-do it all when they raise the boost.
I got where I wanted to be on a Barry Grant carb by just changing jets. I put the jets in the primary that made the cruise good and then put whatever jets in the secondary that put me around 12-12.5 WOT. Dunno. Worked like a champ for me.. I have no idea on the idle..
I don't know what you are reading but they are wrong. You get fuel into the airstream through 3 places: 1. the idle circuit, 2. the transfer slots, and 3. the booster. Oh, forgot the accelerator pumps but they don't effect WOT. The idle and transfer slots have only a small effect on WOT. The amount of fuel that goes into the airstream at the boosters is controlled by the main jets and the PVRC's. So if you want to add or take away fuel at WOT the only game in town is mains and PVRC's. The air bleeds more about working where the mains come in, not the AFR. The power valve is simply a switch that opens to add fuel to the main well just like the main jets. If you are in the 10's on your AFR's the power valve is opening. So to lean out your AFR's you will have to change the mains and/or the PVRC's.
Not totally true. For example if you're fuel curve was good until the latter part then you'd add some air bleed to it. If the whole curve is flat but too rich all the way thru then you need to reduce the main jet size. And depending on the carb the power valve will also have some influence as well. That's why you normally have to go up a few jet sizes if you take the power valve out.
