If the rear isn't pulling it weight in balance you will get too far up the idle and transition slots causing extra fuel to cone too soon in these cruse modes area. You might try opening the rear butterflies more.........often times what happens is your pulling so much air through the front, when you get into the cruise mode your moving enough air to start pulling main circuit fuel...........the fix is more air in the rear blades or lower the floats. Fix 1 area at a time.......idle, cruise, acceleration, wide open. Put your vacuum gauge on it to make sure.......but at cruise you should be pulling more vacuum.......higher rpms with not much throttle should make more vaccum. I bet your starting to pull fuel out the booster.......you should be able to see it free rev slowly from idle up to speed.......I bet around 2500- 3500 you will start to see fuel out the front boosters......if so either open the rear blade.....drill a couple small holes.....something to get more air going through the rear.....and lower front front float
Very good point about fixing one thing at a time. I'll be altering the blade angle on the secondaries tomorrow then. The carb is set up with 1.5 turns on all four corners at the moment. The carb is also 10:1 rich under part throttle acceleration
So that next combo was 11.5 rich at cruise, even with a greatly adjusted secondary throttle blade. Now both front and rear venturi's have their transfer slots showing just a little, and the engine is idling at 1000 cold and 800 warm. It's too rich at idle, which I can easily change. It was 15:1 lean at wide open So, this jetting is starting to look really damn weird. What do I do? It seems to want something like 75 primary jets and then 95 secondary jets. What the heck is going on?
15 isn't rich. That would be lean side at wide open. What did you actually change. Where are you sitting at now So when you say the slot is showing please explain or show pictute.....the idea of too much is sometimes hard to say but easy to see........if you get too much ofvthe slot open the idle srews will seem non responsive... 1000 rom cold idle and 800 warm????? That doesn't add up either....normally war er motors idle slightly higher???
Oh I know 15 is lean, its pissing me off. The current jetting that gave those results is this: 80 primaries/90 secondaries. Primary power valve is 3.5" and the secondary is blocked. And yes, the idle warm was lower than the cold idle. It may be loading up at idle when warm, at a 13:1 rich idle. It may want that amount of fuel when cold. Only a tiny square of the transition slots are open, just like in all those holley manuals and instructions. Exposing any more will cause exactly those problems
Silly question here you had better idle and cruise reading b4 you started all this but worst wide open....when your running wide open gave you checked to see if it pulling vacuum if if pulling a few inches you might need a bigger carb. Try to lean out the idle about an 1/8-a 1/4 turn if it will let you.......jetting plays no real roll in idle and very light throttle.......only the fuel coming through the boosters is controlled by jetting. You might need bigger air bleeds to allow more air into the mixture to help tune it out But the effective jetting from 80/82 with 2 pv in. And 80/90 with only the front pv in is not much change i would guess. Pv are worth 8-10jet size when in the system.....
I went from 80/82 to 76/84 to a removed secondary power valve and 80/90, yes. I just want that 13.5-14:1 cruise. And it is very possible that this 850 DP Holley is too small for this engine. Should I completely remove two of the primary air bleeds to test it out?
Wouldn’t that increase the amount of fuel at cruise when it’s already rich? But yes, I’d say 94 is a good step for WOT
I would tune one thing at a time. Cruise AFR is jets. WOT is Power valve. Cruise should be primarily be on the primaries. Get the cruise AFR at 14.0 to 14.7 with the primary jetting. Forget about the Power and WOT AFR. Once you get the cruise where you want it, then tune the Power system. The Power valve should open and add extra fuel to WOT. The Acc pump should contribute to that. If it goes lean at that point, you may have to open up the Power Valve Channel Restriction (PVCR) to get more fuel. You may also need a longer pump shot.
I may try something dumb like drop the primary jets to 70 and raise the secondary jets to 94. Just to see.
You are chasing your tail. Tune the cruise AFR first on the primary side. It would help to have a vacuum gauge hooked up the entire time. That way you can correlate when it goes lean during different load/RPM. That will also help when choosing the correct power valve. Look at the vacuum level when it goes lean during acceleration.
The power valve does NOT control your AFR at WOT. Google is your friend, John. There's a TON of websites specifically geared to helping you tune a Holley, and Holley themselves have a great set of tutorials on it.
They should not. The PV ads fuel when a specified vacuum level is reached (tip in, part throttle, etc.), and changing it should affect WOT exactly zero, as whatever PV you've selected to put in will go full open at WOT, despite it's "setting" or "number". They all flow the same at WOT, because they're all wide open at that point. Straight from Holley's blog: Let’s start by making sure everybody knows why there’s a power valve circuit and how it works. In every Holley two- and four-barrel carburetor, the power valve is located primarily in the primary metering block, though there are models that have a power valve in the secondary metering block. The purpose of the power valve is to improve part-throttle drivability, air-fuel ratio, and fuel mileage. The Holley power valve is a simple diaphragm with a tapered seat-valve that is exposed on the carb body side to intake manifold vacuum. With high manifold vacuum in a part-throttle situation, this low pressure “pulls” on the valve keeping it closed. As the throttle opens and the load increases, the manifold vacuum will drop. At a calibrated point, a spring inside the power valve will overcome the low manifold vacuum and open the valve. When the power valve opens, it directs fuel from the float bowl into the main well in the metering block. The main well is the circuit that directs fuel into the primary boosters in the venturi of the carburetor. This power enrichment circuit is completely separate from fuel delivered by the main jets and is used to supplement the amount of fuel supplied by the primary jets.
It is strange to me that the carb came with 80/80 jets and 6.5 power valves. I have yet to try this setting, but it seems like it would be pretty rich at cruise. I wonder what the symptoms are of having too small of a carb.
I've read sooo much, and it keeps coming back to maintaining that 8-10 jet gap between primary and secondary. If I do that, I will be probably around 72-74 jets on the primary, and then I'll be stupid lean at every throttle position above 1/2 because of an 80-84 jet on the secondary. I'm glad I installed the wideband, but wow it really makes ya think.
The 850 double pumper should be enough for your new ride, John. It would probably make more peak power with a 950+, but an 850 will run just fine. Hell, I'm running a standard 850 double pumper on my 552 on the street, and it's nice and snappy. It makes more power with a 1050, but the 850 is a ton of fun. You should be able to get your AFRs correct no matter what the carb size is. Put a 500 cfm on it and you can tune it to run "proper", it'll just be choked on the top end when the carb runs out of cfm, but your AFR can still be correct. Same with something like an 1150 Dominator. You can get your AFRs correct the whole way no matter the carb size.
IF I remember correctly from about 8 years ago, I believe I'm at 78/82. I'm at about 3500 ft. elevation. I don't have it written down and I just leave them alone once they're good. EDIT: Honestly, check out Holley's videos and pages devoted to tuning their carbs. They take you step by step.
