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Car runs to rich at cruise rpm

Posted By: rapom

Car runs to rich at cruise rpm - 05/27/13 02:57 PM

I have a Holley 850 ultra hp carb that is running very rich at part throttle cruising. Specs are 84 jets front and back plus 4.5 power valves front and back.

Engine is a 493 with 10" vacuum at idle in gear.

Car is mostly street driven and I know I have a race carb but was wondering if I can do anything.

I was thinking about knocking down the front jets about 5 sizes and increasing the back 5 sizes to make up for the loss.

Thoughts?
Posted By: DaveRS23

Re: Car runs to rich at cruise rpm - 05/27/13 03:12 PM

"I was thinking about knocking down the front jets about 5 sizes and increasing the back 5 sizes to make up for the loss."

Only for a test.

If you decide to keep the smaller primaries, drill the PVCRs out to get the mix back. I find that even their street carbs are a little fat and need smaller primary jets and bigger PVCRs. But the race carbs are much, much too fat at cruise and in the transitions for the street.

If this is a double pumper, they are way fat for the street and require several changes to get street friendly. It can be done, but does require some mods.
Posted By: MR_P_BODY

Re: Car runs to rich at cruise rpm - 05/27/13 03:18 PM

Whats the cruise A/F readings
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/27/13 04:26 PM

This is a race double pumper and I don't have a Air/Fuel ratio gage other than my nose and fuel gage. It is amazing how fast it burns through gas just cruising around.

It idles great and runs great at WOT.

I have never modified a carb other than replacing jets, PV's and accel pump cams and squirters.

Can the mods you are talking about be undone? Kind of worried about the effect a overly rich condition would have on an oxy sensor while trying to tune carb. I have heard they don't last long if they mixture is to rich. So I didn't think I should buy a A/F meter.

I may sell the carb and go with a more street friendly one if I have to.
Posted By: sshemi

Re: Car runs to rich at cruise rpm - 05/27/13 05:04 PM

84s both front and rear with a pv doesnt seem right to me?
Posted By: BradH

Re: Car runs to rich at cruise rpm - 05/27/13 05:14 PM

The new 850 Ultra HP seems to be the one carb in that lineup where Holley really missed on the calibration from everything I've read. I was ready to drop the $$$ on one, but couldn't find a positive review of anyone who had tried one (that wasn't associated with a magazine article ).
Posted By: 383man

Re: Car runs to rich at cruise rpm - 05/27/13 05:22 PM

I run a standard 850 DP on my 63. I had to jet up alot with the 493 and I found that if I went to much on the primaries it would also be to rich at cruise RPM. There is nothing fancy on my 850 as it has all the stock metering blocks and all. So I had to limit the jet size on the primaries as I still run a power valve. I ended up jetting the secondaries more as I found that the limit on the primaries with my setup was about 88 jets and I ended up with 94's in the secondaries. It runs great like that and if I fatten it any more I will up the secondaries. Yea this 493 wants alot of fuel. Ron
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/27/13 06:03 PM

Well, I got it for 1/2 price brand new I figured I could make it work. I had reservations about buying it because of my mostly street driving. Like I said it is great at idle and WOT which I guess is all you need if you are only using it for racing.
Posted By: DaveRS23

Re: Car runs to rich at cruise rpm - 05/27/13 06:08 PM

Don't forget that all that extra fuel is washing down your cylinder walls and fouling your oil. Pull your dipstick, I bet your oil is black as diesel oil after only a little drive time. Not good!

Without a wide band, a good reference book and a little experience the real fix will be a bit of a problem.

You will need small drill bits for the PVCRs. Something in the .060 range +/-. If you over drill them, inserting wires can get you back close.

But the balance between the mains and the PVCRs are just part of the issue. The transition slots are way fat as are all the metering block metering holes. This is a race carb and is metered as such.

All these things can be changed/adjusted, but it is too much hassle for most people.

Every carb I have messed with has needed at least tweaked to the particular engine. And some are not even remotely close. The WOT is usually not too bad. It is the idle, transitions and cruise that typically need the most attention.

Some of the changes can be made seat of the pants. But cruise and some of that really needs to be done with a wide band. And a good Holley book. It takes time and experiments.

The cruise should end up in the 14.7 range +/-. But most of the other adjustments are not so clear cut.

I do not mean to make this sound difficult, but there is a lot going on with the carb from idle to cruise. And all the circuits overlap which makes targeting the issue that much more problematic.

It is too small for your application, but believe it or not, the carb that consistently needs the least amount of mods to get really close to most engines I have messed with is the good old 3310 (750). From 340s to mild 400s, it is one of the best street and street/strip carbs I have seen.

Posted By: Cab_Burge

Re: Car runs to rich at cruise rpm - 05/27/13 06:27 PM

I have found that a lot of the Holley race carbs. are not good street carbs., especially at part throttle You can fix them by limiting the fuel feed on the idle and transition circuits by drilling them and tapping them for #6 brass set screws and then increasing or decreasing the size of the hole in the set screws. You reallly need a wide ban 02 sensor system on the car to be able to get the AFR dead on You can do that by the hit amd miss method, that will take a little longer I did a older Holley 1050 Domintaor 9375 non HP that way, I reduced the idle fuel feed hole size down from around .080 to .045 and then reduced the intermediate fel feed by similar amount percenatge wise, that took the AFR at very light part throttle cruise between 2000 and 2500 RPM from 11.0 to 11.6 to 13.5 to 13.8 AFR I should have reduced them even more and did some more fine tuning but I didn't You can also open up the idle, intermediate and high speed air bleeds on the top of thw carb. to lean the mixtures out also, lots of choices on fine tuning. You really need to make sure that the carb. does not go lean at wide open throttle also while fixng the other circuits on them, all of the circuits can and do affect the wide open throttle mixture some Good luck The main jets affect all of the mixture, I try and fix what is not what I like first, idle, transition, part throttle and then W.O.T.
Posted By: RobX4406

Re: Car runs to rich at cruise rpm - 05/27/13 06:40 PM

What if the rich condition is prior to the mains activating?

Pin gauge or find out what the IFR's sized and go from there. If it's larger than ~.032, I'd find a way to get it sized around .032, reset idle mix, and try from there. The ultra should have adjustable bleeds for all the stuff you need to mess with to clean it up.

I wouldn't step down 5 in front and up 5 in rear to balance, you're asking for distribution issues doing that.
Posted By: Cab_Burge

Re: Car runs to rich at cruise rpm - 05/27/13 07:24 PM

Quote:

What if the rich condition is prior to the mains activating?

Pin gauge or find out what the IFR's sized and go from there. If it's larger than ~.032, I'd find a way to get it sized around .032, reset idle mix, and try from there. The ultra should have adjustable bleeds for all the stuff you need to mess with to clean it up.

I wouldn't step down 5 in front and up 5 in rear to balance, you're asking for distribution issues doing that.

As I pointed out work on one circuit at a time, don't go changing the main jets expecting that to fix the idle or transition richness problems
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/27/13 11:04 PM

I do have and indexed drill set and an old holley tuning book. Not sure how much it would have in common with this carb. But the carb does have the screw in air bleeds at the top which I can play with first. I think I will read my holley book first and get myself familiarized with all the concepts you guys are talking about.
Posted By: Darryls-Demon

Re: Car runs to rich at cruise rpm - 05/27/13 11:39 PM

There is some very good reading on yellow bullets wed site. Go to the naturally aspirated section and look for the 4150 metering thread[it is a few pages in]that thread will keep your head spinning for awhile.
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/27/13 11:59 PM

Thanks, I'll check it out
Posted By: Thumperdart

Re: Car runs to rich at cruise rpm - 05/28/13 12:32 AM

Quote:

There is some very good reading on yellow bullets wed site. Go to the naturally aspirated section and look for the 4150 metering thread[it is a few pages in]that thread will keep your head spinning for awhile.

Agreed..........also motorsportsvillage......good reads there too. What cleaned up my cruise was simply changing the transfer slot hole in the main body from .089 to .055(Thankxxx Cab)and no more loading up...........
Posted By: justinp61

Re: Car runs to rich at cruise rpm - 05/28/13 03:04 AM

Just out of curiosity. Why would you run a 4.5" power valve when you have 10" of vacuum at idle?
Posted By: radar

Re: Car runs to rich at cruise rpm - 05/28/13 04:22 AM

Poor man's version of what cab said with easy instructions:

Big motor has plenty of cruise power with carb barely cracked open =running on idle circuits and transition slots. Choking the primary jets might not get it done. Corner idle circuits can be choked off with the idle mixture screws, T-slots are not so easy- they run pig rich.

T-slot and idle discharge port mixture is decided by the idle feed restrictions (IFR) and the low speed or also called idle air bleeds. The easiest way to attack it is by sticking little v shaped pieces of wire into the IFRs in the metering blocks. You will see that there is the IFR hole and a little angled recess next to it that can be used to hold the V of wire.

I think I ended up using guitar B string wire (.017?) and now my double pumper is really close. I used to have to clean it out by running up the revs constantly but now I can just ease the pedal a crack and putt along behind grandma in her toyota until I get some open road.

Important: the 'corner' idle screws do not 'mix' air and gas, that job is done by the IFR and air bleed working together to make an emulsified mix. This mix is delivered straight to the T-slot and has to go past the corner screw before it can come out the idle discharge port (little hole below throttle blade). Make sure at idle you only show a square of T-slot below the blade.

As you lean out the emulsion coming out the t-slot at cruise you also lean out the idle, so you'll need to spin the corner idle screws to keep the idle happy. Some initial timing is crucial for all this to work too.

A sign this is what you must do is a carb that idles well with the corner screws barely open from screwed all the way in snug. As I tried bigger wire diameters to restrict the IFRs my corner setting went from roughly 3/4 turn out to 1 1/2 turns out. Fine tuning can be done with air bleeds. Some folks will drill the throttle blades- same effect but much harder to undo.

Good luck
Radar
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/28/13 09:57 PM

Well for one thing I sure don't have to worry about them opening early and really richening things up. They were in the carb when I got it and I always read that you should have the power valve number 1/2 of the vacuum number.


Thanks for the easy to understand writeup radar
Posted By: BBR

Re: Car runs to rich at cruise rpm - 05/28/13 11:08 PM

motorsportsvillage is locked down.

This is the new site:
http://racingfuelsystems.myfunforum.org/index.php
Posted By: sshemi

Re: Car runs to rich at cruise rpm - 05/29/13 06:14 AM

Why not just turn in the mix screws?
Posted By: radar

Re: Car runs to rich at cruise rpm - 05/29/13 10:01 AM

Quote:

Why not just turn in the mix screws?



Because the term 'mix screws' is a misleading. The idle corner screws don't determine the air/fuel mix of the emulsion that comes out the idle discharge ports, just how much of it can come out. Like an adjustable jet. The same emulsion is delivered to the T-slot which is almost never adjustable. This circuit can be crucial to crisp throttle and not fouling plugs in slow traffic.

Since a strong motor can cruise well at very small throttle openings it is common for the cruise mix to be supplied mostly by the transition slot. The T-slot is non adjustable in most metering blocks, but the emulsion that is supplied to it is tunable by messing with the Idle Feed Restrictions (IFRs).

So if a standard preset of 1.5 turns out from lightly seated is too rich of an idle you can screw in the 'idle mix' screws to limit the emulsion delivered to the idle discharge ports. Your idle is cleaned up but the T-slot is still pig rich- especially with a big motor sucking hard on it pulling air past a mostly closed throttle.

A strategy that worked for me is to choke down the IFRs until the light throttle cruise cleans up, which will also lean out the emulsion that is metered by the mix screws, so now they get unscrewed to fatten the idle back up.

In my limited experience wrestling with double pumpers there seems to be a magic setting for the IFR- when you choke it down to the point where the mix screws end up around 1.5 turns out the t-slot is gonna be close and can then be fine tuned with the low speed air bleed. I started to notice that on carbs with a real fat off idle cruise the 'mix screws' were more like 3/4 turns out before limiting the IFRs, even after opening the secondaries to idle off them too.

This is why drilling the butterflies can be a 'magic' fix but not easy to take back or adjust later. By the time you are on the mains the hole is not leaning out the overall mix much.

I asked a lot of questions here about this stuff but I ended up having to pour over holley books and web articles to figure this stuff out. For some reason this is like secret knowledge. I've learned a ton on here building my a-bodies and I hope I can help give back a little!

Cheers
Posted By: sshemi

Re: Car runs to rich at cruise rpm - 05/29/13 10:21 AM

I have found that almost always the throttle blades are not set correct when rich at idle/transfer.
I used to think, hey how important can it be, well it is and its really sensitive also.
But if it is set correct you are right, decrease the ifrs but this will also lean curb idle.
Sometimes it can be really hard to make the idle and transfer match good.
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/29/13 01:56 PM

Do I assume right that I should also restrict the secondary IFR's since I have four corner idle on my carb?
Posted By: radar

Re: Car runs to rich at cruise rpm - 05/29/13 04:13 PM

Yes
Posted By: RobX4406

Re: Car runs to rich at cruise rpm - 05/29/13 04:52 PM

Quote:


But if it is set correct you are right, decrease the ifrs but this will also lean curb idle.




Back the mixture screws out a bit.

The mixture screws don't mix the air/fuel from the IFR/Air bleed. The IFR/IAB is mixed before hitting the mixture screw, at that point you are allowing a designated amount of the pre-mixture in the idle ports.
Posted By: Cab_Burge

Re: Car runs to rich at cruise rpm - 05/29/13 05:22 PM

What is the List number(including the dash number, IE 9375-3) on the carb. you bought and are trying to make better?
Posted By: DodgeCharger

Re: Car runs to rich at cruise rpm - 05/29/13 05:46 PM

What is the purpose of the power valve? I haven't had a carb with a PV in years. My carbs run fine without them.
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/29/13 08:45 PM

List number is 80804 and the number beneath it is 0622

I couldn't find a dash no.
Posted By: justinp61

Re: Car runs to rich at cruise rpm - 05/29/13 10:25 PM

Quote:

Well for one thing I sure don't have to worry about them opening early and really richening things up. They were in the carb when I got it and I always read that you should have the power valve number 1/2 of the vacuum number.


Thanks for the easy to understand writeup radar



Ok. I've never read or heard about the power valve being 1/2 of the vacuum at idle. Everything I have had 1 1/2" less than idle vacuum for the power valve. More than one way to skin a cat I guess.
Posted By: BSB67

Re: Car runs to rich at cruise rpm - 05/30/13 01:04 AM

Quote:

Quote:

Well for one thing I sure don't have to worry about them opening early and really richening things up. They were in the carb when I got it and I always read that you should have the power valve number 1/2 of the vacuum number.


Thanks for the easy to understand writeup radar



Ok. I've never read or heard about the power valve being 1/2 of the vacuum at idle. Everything I have had 1 1/2" less than idle vacuum for the power valve. More than one way to skin a cat I guess.



The 1/2 vacuum number is a suggested starting point for tuning. It is often portrayed on here as if it is the answer.
Posted By: Cab_Burge

Re: Car runs to rich at cruise rpm - 05/30/13 02:27 AM

Quote:

List number is 80804 and the number beneath it is 0622

I couldn't find a dash no.

I tried finding that carb. number on Holley tech pages to see what the stock jetting, squirters and so on where from the factory, no such number listed Sorry.
Posted By: sshemi

Re: Car runs to rich at cruise rpm - 05/30/13 07:29 AM

Summit have it. Stock with 84s with dual pv.
Iab 67 witch to me sounds a little small.
Posted By: BradH

Re: Car runs to rich at cruise rpm - 05/30/13 05:38 PM

I was pretty sure there was a post on motorsportsvillage.com maybe a year or so back where someone had disassembled all of the new Holley Ultra HPs (650 thru 950) and posted how each one was configured w/ bleeds, jets, etc., "as is" from Holley. I did just try a quick Google to see if I could find it easily, but didn't come up w/ the right links. Probably worth looking for on your own, though.
Posted By: Thumperdart

Re: Car runs to rich at cruise rpm - 05/30/13 05:55 PM

Quote:

Summit have it. Stock with 84s with dual pv.
Iab 67 witch to me sounds a little small.

My 1050 hp dommy came w/37 hi-speed and 84`s ft. and rear w/6.5 pv`s and was rich at cruise but dead lean 17.1 at wot fwiw.............tweeking is definately in order. Good luck............
Posted By: Cab_Burge

Re: Car runs to rich at cruise rpm - 05/30/13 07:05 PM

Try reducing the transfer slot fuel feed(all four ) by about half its diameter Take the carb. off the motor and remove the metering blocks, both of them and look at the transition slot in the carb, it is the small narrow slot that the throttle blades straddle on the front of the throttle plate The idle feed hole is below the throttle plates and the transition slot is centered in the throttle plate, it should have the throttle plates centered or a little above or below center Look and find the hole on the main body that feeds that circuit, measure the diameter of it with a numbered drill bit set and then tap and insert a blank #6 brass set screw and drill it(the insert) with the numbered drill bit you want to use to limit the fuel feed
Posted By: rapom

Re: Car runs to rich at cruise rpm - 05/31/13 08:59 PM

I have everything to do the job but a small tap set. Looks like a good excuse to buy a set. Of course I'm going to cringe drilling into this new carb.

Not sure when I be getting the bit set but I appriciate all the brainstorming that is going on.

I may move this carb to my Camaro which has a 509 BBC that is more of a race car which I still drive on the street.

My Coronet is more of a driver which is making me look at fuel injection more closely. I still plan on getting this carb to run right on my Coronet though as I'm going to have to save up for fuel injecting it.
Posted By: BBR

Re: Car runs to rich at cruise rpm - 05/31/13 10:21 PM

Tapping my 1050's transfer slots.


Brass set screws from McMaster-Carr
Posted By: radar

Re: Car runs to rich at cruise rpm - 06/01/13 12:00 AM

Quote:

What is the purpose of the power valve? I haven't had a carb with a PV in years. My carbs run fine without them.



The power valve is another non adjustable stab in the dark by holley. Ideally you want to be able to lean out the primaries so that under normal conditions (med to high vacuum) the air fuel ratio provides decent power and economy. When you really step on it a little first the acc. pump covers the initial gap when the vac. drops. Then PV opens, providing a boost of fuel where the primary jets would have been too lean.

The problem with this is that the Power Valve Channel Restrictions are another non-adjustable orifice. So when the PV opens it might go pig rich, or pinging lean.

The thing to do is get the idle and transfer slot settings close, then work on the primary main jets with a vac. gauge and AFR meter. Get to where you can drive with a crisp throttle if you drive like a regular old lady. Take note of how low the vac. reading is when the AFR starts to go too lean to give good power.

Then put in a PV that opens around that vac. Go test it. Notice when it opens the mixture will fatten a certain amount. Now you can restrict or enlarge the PVCRs and swap PVs to open earlier and later. This is a balancing act. As long as your regular cruise is good and WOT is giving the best times at the track you will have to decide weather you want a little richer or leaner here or there. Having a good AFR meter really shows you how much of a compromise a carb is compared to EFI.

I personally am happy if I know how to drive my car so that it will have good manners, do what I expect, and not foul out putting around.
Posted By: BradH

Re: Car runs to rich at cruise rpm - 06/01/13 12:56 AM

Quote:

The problem with this is that the Power Valve Channel Restrictions are another non-adjustable orifice.


Better look again. Lots of modern metering blocks, including the ones that come on all the Holley Ultra HP series, have replaceable jets for the PVCRs, along w/ the IFRs and emlusion well circuits.
Posted By: sshemi

Re: Car runs to rich at cruise rpm - 06/01/13 07:48 AM

I agree the ultra hp should have everything adjustable.
Posted By: rapom

Re: Car runs to rich at cruise rpm - 06/01/13 12:26 PM

There is so much good info here this should be saved in the tech archives.
Posted By: Darryls-Demon

Re: Car runs to rich at cruise rpm - 06/01/13 07:55 PM

Quote:

Quote:

The problem with this is that the Power Valve Channel Restrictions are another non-adjustable orifice.


Better look again. Lots of modern metering blocks, including the ones that come on all the Holley Ultra HP series, have replaceable jets for the PVCRs, along w/ the IFRs and emlusion well circuits.



If you are going to try to use an Ultra HP on a street strip car you need to order your self a wide band at the same time, you will need it.
Posted By: moparniac

Re: Car runs to rich at cruise rpm - 06/01/13 08:34 PM

Quote:

that is running very rich at part throttle cruising.



what rpm are you talking and what is going on to tell you your rich? did you check plugs! wideband is a good tuning tool.
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