I need some help with tuning my new Holley. I currently built a new combo with a 499 stroker low deck. Holley street dominator with solid flat tappet .050 = 251 intake and 256 exhaust, .567 lift at 110 lobe. 3:91 gear, 4 speed.

I have always used the Edelbrock 800 avs on all my builds. I have had really got success with tuning them, but I am not familiar with the Holley's.

On this build I decided to use a double pumper.

I am having problems with a very rich condition at cruise. I have setup my idle mixture with a vacuum gauge and o2 gauge.

I have 9-10 inches at idle and my o2 read 13.5-14.0. I replaced the 6.5 stock power valve to 4.5.

It idles fine and currently has no hesitation when accelerating from cruise.

When cruising around (ambient temp 90f) the o2 shows 11.8-12.8, If I let off on the accelerator it goes up to 13.5. These readings are the same at 40, 50 or 60 mph. Occasionally the o2 drops to 9.8-10.8 when cruising and the car starts to buck. A couple times it has stalled with those readings.

Fuel pressure at idle is 5.5 to 6 psi with a mechanical pump. Not sure what it is at cruise.

It runs okay at cruise when the readings are 11.8-12.8, but I would like to lean it out. What can I do? I was thinking of changing the primary jets. I cannot replace the air bleeds because they are a fixed diameter.

I don't know what it reads at WOT because I am trying to breakin this new clutch. On the engine dyno with open headers the plugs showed good readings. I am thinking with the full exhaust it will probably be slightly richer.

Timing is at 34 total and 16 base. I have set the float level to the bottom of the sight glass.

Gotta jet for that carb. Try a couple sizes down on the primary. Vacuum advance dizzy? If not, try one.

Thanks Darth, I am running the msd billet distributor so I do not have vacuum advance.

Double pumpers are pig rich on the transitions and at cruise. They are jetted for the track. The simplest thing to try is to drop down 5 jets on the primary and open the PVCRs several thousands to compensate. You need a wide band to re-balance the WOT.

Shoot for mid 14s for the cruise, but you will need the enrichment circuit to come in sooner with that leaner and cleaner cruise. Probably an 8.5 to 10.5 power valve. You can disconnect the secondary linkage so that you can concentrate on the primary mixes. The secondary WOT is usually pretty close.

What is the afr at 3500-4000 rpm cruise? This should get you close on the primaries. I wouldn't mess with the PVRC until I checked that. Also you didn't mention what high speed air bleeds or idle feed restrictions you have. Both will have an effect on cruise afrs.

BTW your idle vacuum will have no effect on the power valve.

i would first work on the idle feed restrictors (IFR's) and the primary jets (the 3500-4000 rpm cruise that justinp61 mentioned).

I will have to double check the A/R at 3500-4000 but I am pretty sure it is 11.5 to 12.5. The high speed air bleeds are fixed. Were are these idle feeds located? I have the billet metering blocks.

This is what I would do first. If you think about it when you are cruising most of the time you are running of the transfer slot circuit which can be leaned out by the idle feed restriction. I know most of my part throttle cruising I am running on the tranfer (transistion) slots so if its fat at part throttle cruise I would lean out the (IFR) idle feed restrictions. If you are happy with the rest of the carbs settings then leaning the idle feed restrictions wont effect the other circuits but you may just have to adjust your mixture screws when done. I believe most billet metering blocks should have jets for the IFR. In the older carbs we would put a small piece of wire in the IFR which also would lean it out some. But I believe yours should have jets in them already. They (the IFR) can also be drilled and have jets installed in them as "Hemmings Muscle Machines" mag had an article about doing that a few months back. Ron

Ron, I will have to take the metering blocks apart and check if the IFR's can be replaced. Does Holley sell these IFR's ?

If it's that rich I'd pull two jet sizes out of the primaries and recheck. Do this before you mess with the ifr's. Changing the primary jets will affect the cruise afr's, at least it does on mine.

What Ultra do you have? I thought they all had screw in air bleeds.

A 500" engine with an 850 carb will likely cruise on the main circuit not the idle circuit. Although the OP should check to be sure. But he said that his idle is good, so leaning his IFRs is not a good place to start in my opinion. Besides, the main jets are the only items that screw in. Everything else requires drilling and threading in order to adjust. (Of course there are always wires.......)

The PVCRs do not have to be drilled at first. The mains can be dropped down how ever many sizes you wish and then the cruise A/F checked. But if the mains end up needing to be sized down, then the PVCRs will need to be enlarged to compensate.

Again, I think that the easiest and best start would be to disconnect the secondary linkage, drop down several main jet sizes and test drive the cruise. Just be aware that the power circuit will be lean until the PVCRs are opened up.

I have an 850 DP with the annular boosters and spend most of my time cruising on the transition circuit... This is on a stock stroke engine though.

Good news is that you have an O2 gauge, that makes tuning easy. Just imagine what a pain it was to have those old Holley DP carbs back in the 70's and 80's without O2 sensors.

Just lean out the main jets until the cruise AF is correct and then go from there.

When you tune a carb you start with the idle circuit and work your way to the power circuit.

I don't know why you changed the power valve. I'm thinking you might have gone the wrong way there. Do you have a vacuum gauge in the car? If so, you should watch it while you drive. Head up a long hill and see where the vacuum is when it needs more fuel.

Agree with AndyF. Do the simple things first. On your carb that is reducing the size of the main jets. I'm guessing you need to remove at least 4 jet sizes, and it will probably end up like 5 or 6.

Don't you dare start messing with air bleeds. That's for fine tuning later and as you have said yours are not screw in, so that makes it much harder to undo any changes. Also if you are not familiar with Holley carbs that's for someone with more experience to attempt.

Get the main jetting right and then you may want to check on the power valve as Andy said. You said you have 9 - 10 inches and the 4.5 would be in the Holley-recommended range, but they're not an absolute. Without the extra richening of the main jets you have now, the power valve might not open soon enough.

R.

My point was that if the carb is jetted good for power right now I sure would not be dropping jet sizes for a cruise problem that I bet is mostly all on the transistion circuit. Once my carb was jetted at the track for power I am not going to jet down. I would lean down the IFR which is no big deal on a Holley type carb. Lean it a small amout and you should still be able to adjust your mixture for a good idle as I did on mine. But if you feel your rich all over then yea I would jet down then. Myself I like to jet my carb for best power and mph and then work the other circuits to fine tune it for cruise and idle. That way you are not affecting you power jetting. Also make sure the power valve is coming in at the right time but I dont think it will be open on a part throttle cruise unless you have it way off. I know when I cruise at part throttle I barely have the gas pedal pushed down any. Why would you want to set the idle and cruise without having the main jetting right first ? If you tune the cruise and idle circuits and then find you need to jet up at the track for power you then may have to retune the other circuits. I tune for full power first so I know I wont be changing my main jets and affecting my full power. Ron

Guys, I took the carb apart and found a small piece of aluminum sitting on top off one of the IFR's on the primary side. The IFR's can't be replaced only drilled.

I found that the carb has 80 jets on all four corners. I removed the two primary ones and replaced them with 78's. Should I start here or go down another 2 sizes?

I know I should look at wot, but I have to keep it away from wot for 500 miles in order to properly break in this clutch. I might have to change these jets later but for know I can't drive it this rich.

You are probably going to need to buy a set of billet metering blocks to get that carb dialed in. You can go old school and use epoxy and solder and stuff like that to adjust the stock metering passages but it is fairly inexpensive these days to just order a set of metering blocks from BLP or QuickFuel and be done with it.

Andy, I have the billet metering blocks now, but I guess you are referring to the removable IFR's on the billet blocks.

Should I go back to the 6.5 power valve or leave the 4.5 ?

the 6.5 PV is probably closer to what you need.

the billet blocks, it seems they would have replaceable IFR's...
i will see if i can find a link to tapping the IFR's in the low psoition and post it here. most people agree the low position works better.

also, you have a PV and the jetting is the same on all four ocrners of the carb???
where did the carb come from? is there a PV on the secondary side too?

what is the part number for the carb? do you know what the baseline jetting was?