Help With Holley 850 Ultra Double Pumper Tune Up

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?

Sorry as I did not realize you have to keep it from WOT for a bit. Then do what works best for you now. Course you may have to change the main jets later if you tune for WOT. I was also curious if you have both a primary and secondary power valve since jetting was 80 on all 4 corners ? I would guess it does have both power valves or someone has been in the carb before ? Ron

The carb came directly from Holley. I called them to verify the factory jet sizes. They mentioned 80 in all 4 corners and two 6.5 power valves. Why they used billet metering blocks with pressed in IFR does not make sense???

part # 076-851bk

I reinstalled the 6.5 power valves and went down on the primary jets from 80 to 78. Tested the car and found the AF at 11.8-12.5, I then changed the primary jets again from 78 to 76. The AF now is 12.5-13.1. Still runs good at cruise and no hesitation. Have not tested WOT yet. I am going to change the jets from 76 to 74 tomorrow. I left the secondary jets at 80 for now.

Where should my cruise AF be? I am thinking 13.5-14.5

I have the idle at 13.5-14.0.

I would not go to 74s without at least trying WOT with the 76s first. IMO it will probably be pretty lean with 74s at WOT...

""Where should my cruise AF be? I am thinking 13.5-14.5""
""I have the idle at 13.5-14.0""

You are doing the right thing by creeping up on the A/F ratio. Your cruise A/F "range" looks like a good target. Once you are in that range, test to see where the "lean limit" is on your combo. As you lean it out a little at a time, listen for detonation. Once you start to hear it, then you know what is the lean limit on your combo, then you can richen it back up a bit.

I think your idle may also be in a good target range, but once again, you need to test to see what the lean limit is to your idle too. Some can idle/cruise at 13.4 and some can idle/cruise at 14.4.

Nice job!!

If you decide to relocate your ifr here's a good read.
http://racingfuelsystems.myfunforum.org/Relocating_the_Holley_Idle_Jet_about18.html

It WILL be lean at wide open after pulling that much jet out. And it looks like it still needs even less jet. The OP says that he needs to avoid WOT for now, so continuing to test the cruise with less jet is not a problem.

The idle is okay right now and he is moving in the right direction on the cruise. Keep pulling jet until the cruise is clean. Then, when possible, drop the secondary linkage and start drilling the PVCRs until the WOT on the primaries is good. Opening the PVCRs bigger will replace the fuel being taken out with the smaller main jets. And it will want that additional fuel sooner now.

We usually go with a 9.5 or 10.5 power valve. You really can't get too quick of an opening. The reason it didn't need that early of an opening point before is because it was so rich already. Now that it is leaner on the cruise, it will need the additional fuel sooner.

The track is the best place to set the WOT, but initially shooting for low 13s will get it close enough to dial in without being too rich. It is easy to drill it richer, but harder to lean it back down if the holes get too big.

We have done quite a few Holley 3310s and double pumpers this way. They are always rich on the cruise. Pull jet until the cruise gets happy, open the PVCRs until the WOT gets happy, and get the power valve open in time to eliminate any lean stumble has always worked.

The most common mistake people make with Holley carbs is that they change the jets to control air fuel ratio at WOT. As Dave points out, the PVCR is what should control the "extra" fuel for WOT. It takes more work to do it right, but you end up with a better carb when you do it right.

With a DP carb you can also set up the secondary side to be richer since it usually isn't kicking in for freeway cruise anyway.

Yea but you cant do that if you block off the power valve's. For racing I prefer to block off the power valves. Ron

For tuning, you can use a power valve plug to take the PV out of the metering equation. If it is still rich at low speed cruse (Throttle just cracked), you should look at using a smaller Idle Fuel Restrictor (IFR). I would not use a larger air bleed because that will delay when the main metering starts to flow.
At high speed cruse (Throttle open past transition circuit) tune with the main jets.
Replace power valve plug with power valve and see how the AFR looks when transitioning from cruse to power.

Here is the update. I installed the 74 jets on the primary. The cruise went up to 13.0-13.5. Under load from cruise I started to notice the AR fuel at 15-15.5.

I went back to 76 jets on the primary. The best I can get the cruise is 12.8-13.2. When under load from cruise I see 13.5-14.0 on the AF. No hesitation, and feels happier. The issue now is the IFR's are fixed. I might have to look at other metering blocks.

Next I am going to install a vac gauge in the car and see what readings I have.

I am sure this will be okay to cruise around till I can test WOT.

what is the vacuum reading where you are going lean?
i would throw an 8.5 PV in on the primary side and see if it still goes in the 15.0 AFR area with the light-moderate load.
if so, then you probably need to open up the PVCR if you want to keep the leaner jets in.

if you're already getting the transition circuit cruise where you need it then the IFR's are probably fine as is.

The "under load" is where the PVCRs come in. They are the power enrichment circuit. Do not use the mains to set that. Continue to pull jet until the cruise gets happy. Then throw more fuel at it when under load with the PVCRs and give it to it sooner with an earlier opening power valve.

Do not mess with the IFRs now. If there is nothing wrong with the idle, then don't mess with them. The transition slot may need some attention after you lean out the cruise. But unless you have an issue with the idle, leave the IFRs alone. At least for now.

See how the engine likes a cruise A/F of 14-14.5. The tip-in from a lean and mean cruise to more load will be the next challenge after you get a happy cruise. But the transition slots, PVCRs, and power valve will address that.

You are clearly going in the right direction. Keep it up.

"" I installed the 74 jets on the primary. The cruise went up to 13.0-13.5.""
- You are going in the right direction!!

""I went back to 76 jets on the primary. The best I can get the cruise is 12.8-13.2.""
- You took a step backwards. 72 jets may get you in the upper 13's and 70 jets may get you into the low 14's. Keep testing

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""The "under load" is where the PVCRs come in. They are the power enrichment circuit. Do not use the mains to set that. Continue to pull jet until the cruise gets happy. Then throw more fuel at it when under load with the PVCRs and give it to it sooner with an earlier opening power valve.""

- This is what you want to do after you lean out the main jets to get your cruise A/F where you want it.

This carb is driving me crazy. I went down to 75 jets and it's still 12.8 - 13 af at cruise. If I get in the throtle at a light cruise I sometimes feel a small hesitation and the af goes lean to 14.5 then goes rich.
At various times when I leave a traffic light, from first gear to second shifting at 3000-4000 rpm it falls on its face and the af goes to 10.8.
I installed a vac gauge and cruising around just holding a constant speed at various speeds I see the vac at 15 inches.

I did a small wot pass and I saw 12.2 af.

What is next?

Current setup primary 75 and 6.5 pv
secondary 80 and 6.5 pv

80 mains.....11.8-12.8 cruise
78 mains.....11.8-12.5 cruise
76 mains.....12.5-13.1 cruise
74 mains.....13.0-13.5 cruise with slight hesitation




Why not continue to try smaller main jets and an earlier opening power valve?

499 stroker with a Holley 850 carb. I read the newer 850's were really 750's with an 850 TP. I've tried 750's on my 440 and they all seemed hard to tune,to rich at idle to lean at wot. very hard to get everything right. I put a pro form 950 body on an old 850 dp that uses the 850/950 tp and my combo has never ran better and every adjustment has been easy and responsive.

It just sounds like to me your carb is to small for your combo. you need more cfm IMO.

The OP may well need more CFM for maximum performance @ WOT, but he is trying to get his cruise happy. And there is no reason he cannot do that with an 850. The double pumpers are track oriented carbs which are very rich for street cars which is why the OP is being forced to change the tune so much.

But they can be tuned to give satisfactory street manners, just like a Dominator can.

And yes there would have been carbs that would be closer to what he needed right out of the box, but this is what he has and it can be made to work.

IF he wants to put the effort into it.

I don't know if you can tune a carb very well that is to small for the engine. I agree that you can lean it out.

Pick ur poison..