# Experiences in Carburetor Tuning (was: Question...)



## BearGFR (Aug 25, 2008)

I'm in the process of tuning my new carburetor after my recent rebuild, and am working through some issues. Would folks here be interested in a running commentary of what I'm working on and how I'm doing it? I've got at least one problem that I'm still trying to figure out - I think I'm "on its trail" but it's still not fixed.

In the past I've been very vocal about how much I like Quadrajets. That hasn't changed, it's just that my engine I believe is to the point where my QJet isn't big enough to feed it so I've told myself I'm being 'forced' down a different path. 

Up to ya'll - let me know - and oh, if anyone has already dealt with and solved the problems I'm hitting, myself being a first-time Holley newbie, I'd sure love to hear the solution.

Thanks,
Bear


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## soberjoe (Nov 28, 2016)

IMIN!
I seem to learn a ton of good info from guys like you Bear!


Sent from my iPhone using Tapatalk


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## HickBoy (Aug 5, 2018)

+1 for your troubleshooting story. I have a very old Carter 9635 and a newer 9635SA that both need rebuilding. The more I read about what others are doing makes it easier for me to take the plunge and try the rebuild myself...


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## bigD (Jul 21, 2016)

"...I like Quadrajets. That hasn't changed, it's just that my engine I believe is to the point where my QJet isn't big enough to feed it so I've told myself I'm being 'forced' down a different path..."



Just curious. There are several Pontiac Super Stockers running 9's, with 750 Q-jets. Guessing that these engines are making around 600hp. So, exactly what would be the limit of power that a correctly built 800 cfm Q-jet could handle ? As you probably well know, SMI even makes a 900 cfm Quadzilla, tho I don't know how streetable it would be.

https://cliffshighperformance.com/simplemachinesforum/index.php?topic=598.0

But, my engine guy won't use anything but a 1050 or bigger Dominator on his 495 & bigger engines.


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## BearGFR (Aug 25, 2008)

bigD said:


> Just curious. There are several Pontiac Super Stockers running 9's, with 750 Q-jets. Guessing that these engines are making around 600hp. So, exactly what would be the limit of power that a correctly built 800 cfm Q-jet could handle ?


Dunno... I think it takes more than 600 hp to get into the 9's unless the cars are super light. But anyway, honest - I really do like that 455 SD Qjet I have and according to Cliff, it flows more than 800. I started down the road I'm on now for two main reasons: 

CFM. Everyone has an opinion of course and I've researched a zillion of them. What I finally decided was close to the truth was that my 461 needs about 870 CFM at 6500 rpm. It's not going to see 6500 maybe a couple times a year, if that, but I wanted to plan for that plus some headroom.
Intake Manifold. I wish to goodness I could use my stock cast iron intake, but it's just not possible. When I set it on top of the engine there's about 1/8" of open intake port showing *above* the edge of the cast iron. These days no one that I know of makes a decent spreadbore intake that will cover these ports. I've got an old original Torker 1 that I was running on the car that will fit these ports, and I did back to back dyno tests comparing it to my stock factory intake back when I first built the engine in 2010 with #722 heads at that time. It lost quite a bit of bottom end compared to the factory intake and even though it made some up after 5000 RPM, I don't think it was enough to make up for what it lost down low. Plus throttle response with that manifold isn't great. A friend of mine who has a 72 convertible with a mild 455 (not nearly as stout as my car) is running a Performer RPM with a 750 Demon and that thing has INSTANT throttle response everywhere. It's impressive - every bit as snappy as any fuel injection system if not better. Part of that is going to be due to idle vacuum but my goodness - even with my previous cam that made 14-15 inches at idle - running the SD Qjet on the Torker1, it wasn't even in the same county as his car in terms of responsiveness.

And I guess, part of me was tired of arguing with all the brand H guys. I figure at least I'm going to learn every bit of what these things are about while I'm at this so the next time I get into it with one of them I can speak their language. I've learned a lot already... I'm still a big fan of Rochester and wish I could keep running mine.


Bear


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## BearGFR (Aug 25, 2008)

Getting into the story now I guess...

My engine and car at the present time:


461 cubic inches (4.25 stroke x 4.155 bore)
Heads: 72cc Edelbrock round port. "Entry level" port work by Dave Wilcox. 2.190 intake valves, 1.77 exhaust valves.
Cam: Bullet solid roller. 251/257 @ 0.050, 110 LSA, installed at 106 ICL. .625/.623 net valve lift after allowing for valve lash
Rockers: Crower stainless, full roller, 1.5:1 ratio
Lifters: Crower solid roller, HIPPO oiling, needle bearings, standard height, cutaway
Valves: Ferrea - Ram Air IV length
Springs: PAC double. Installed height 1.910. Seat pressure 230, open pressure 570
Retainers: PAC Titanium
Locks: Isky 7-degree super locks
Timing set: Rollmaster double roller (.005 short due to align hone)
Balancer: Romac - SFI rated
Compression: 10.3:1
Crank: Eagle forged
Rods: Eagle H-beam forged 6.700 length
Pistons: Ross forged, full floating pins (double spirolocks) D- shaped dish
Windage Tray and Crank scraper: Spotts performance
Rotating assembly neutral balanced by Butler performance
Oil pump: Luhn Performance 80 psi
Intake: Northwind - single plane
Carburetor: AED Performance 850 HO Annular
Fuel pump: RobbMc 1100 mechanical, set to 6 PSI output pressure, RobbMc regulator at carb inlet (set to 5 psi)
Flex plate: TCI SFI rated - neutral balance
Converter: Tri Shield Performance 9.5" (I'm REALLY liking this! Drives like a stocker until you hang your foot in it)
Transmission: TH400
Rear: Moser 9" - Wavetrac diff - 3.50 gears
Instrumentation: Factory Rallye gauges supplemented by AEM Digital X-series Coolant Temp, Trans Temp, Oil Pressure, Wide band UEGO Air/Fuel meter
Ignition: HEI with Davis "Dyna Mod" module


First challenge after getting it running and driving has been trying to balance the settings for idle and low speed part throttle cruise. When I first got it running, I was able to accomplish a reasonable idle "in gear" at about 750-800 RPM, A/F ratio in the 13 to 14 range which produced an idle vacuum of around 7-8 inches Hg. The idle was fine. However cruise was not. Even the slightest pressure on the throttle, enough to barely start the car moving and send the rpm up to about 1500 would send the A/F mixture plummeting into the mid 9's, even high 8's. There it would stay pretty much 'everywhere' at a steady state cruise. Getting up to around 60mph would see it creep up into the high 9's, low 10's but this was still WAY too rich. Getting dangerously into fuel wash territory - so rich that raw fuel could be getting into the cylinders and diluting the oil. 

I tried jetting the carb down which did nothing really. I tried fiddling with idle mixture to get it as lean an idle as I possibly could. Right away I got into a Catch-22 situation. If I adjusted for a lean idle in neutral at around 900 to 1000 rpm, say mid to upper 14's on the A/F meter, as soon as I put it into gear it would shoot up WAY lean - 16's, 17's, 18's - and higher. A few times I saw it go so lean that it was above the gauge's ability to register it. I wasn't able to find an idle mixture setting that would let it idle at 800 rpm in gear without it going super rich driving. I couldn't figure out what was going on. I bought Dave Vizard's book on tuning Holley's but didn't find anything that addressed this specific problem. I started reading everything I could find on the net. That's when I found this thread on a Mopar forum:

Holley Rich at Light Throttle | Moparts Question and Answer | Moparts Forums

It seemed to fit with what I was seeing. The thread also mentioned getting into a situation of not being able to get both idle and cruise into an acceptable mixture range at the same time, and why.

I found threads that mentioned "transfer slot restrictors" that seemed to make sense. The transfer slots provide fuel to the engine during the 'transition period' when the throttle has moved off idle but hasn't yet been opened enough to cause the main circuit/boosters to come online and start feeding fuel. This engine makes so much torque that the majority of the time it's running on the transfer slots, even at 50-60 mph. The force that causes fuel to feed through the idle circuit and also through the transfer slots is primarily engine manifold vacuum - not air flow through the main venturis. The problem is, at an 800 rpm idle manifold vacuum is less than 10, but as soon as rpm starts to come up manifold vacuum comes up too, and fast. I hooked my gauge up so I could read it in the car, and once the car gets rolling and it's running at 1500 rpm or better, manifold vacuum is at 20 or better so it's "sucking" a lot harder on both the idle circuit and the transfer slot circuit. This explained how it could be 'right' at idle but sloppy rich at cruise. The problem then was how to get fuel flow to even out over such a wide range of manifold vacuum.

.... to be continued

Bear


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## geeteeohguy (Feb 2, 2008)

Bear, great stuff and thanks for posting, but please clarify why you can't run the GM intake on your heads. I could of sworn that a lot of people run the stock Pontiac Q-jet on E-heads and KRE heads, etc. What does Cliff say? I think you are giving up a lot in the 'real' rpm ranges running a sub-par intake. I know that if I had a 461, I'd want to run it at 1800-3000 rpm 99% of the time and over 5000 rpm once a year. Low end torque and crisp throttle response are what make a big heavy GTO move out, as you well know!! BTW, have run Holley carbs on Pontiacs, Fords, Chevys, and Mopars I have owned....and they always seem to work well to make excellent power, but are always a bit on the thirsty side due to their coarser calibrations, in my experience. They always drove smooth and surge-free. 
Jeff


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> Bear, great stuff and thanks for posting, but please clarify why you can't run the GM intake on your heads.


I tried, believe me. Back a few years ago when I first got these heads, to replace the #722 's, the first thing I did was to sit my factory intake up on them. It was a big surprise when I could see 1/8" of exposed open port ABOVE the edge of the intake manifold. I think it's not so much from the overall port height as it is where they're located in the heads. I was running my factory iron intake with the #722 's and I had to work it over pretty good to get it port matched which left only 1/8" thick gasket surfaces at the top and bottom of the ports, but it worked. A Ram Air IV intake or an HO/SD might work because they're taller than the regular ones. I looked into that and got the impression that all the reproduction ones are pretty poorly made, and genuine ones are out of sight cost wise, that is when you can find them. I just checked Ebay and there are some there - the cheapest one is $1,276.00 and that's with no heat crossover. 

Anyway - right now I'm getting pretty frustrated and discouraged with the whole thing - again. I've got some things that I'm worried about from having it running so rich for awhile.

Bear


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## geeteeohguy (Feb 2, 2008)

That last sentence is a cliff-hanger, Bear. If your oil didn't get too diluted, you'll be fine. I've seen a lot of this over the years, and it has to be a chronic issue to wash the rings....very hard to do in a drive or two. I don't analyze things as much as you do....due to lack of brain power. I go simple and basic on this type of stuff. Think about it: every carb ever made has to idle, transition from idle, cruise, and go WOT. Fuel ratios will change from around 15:1 at idle, should be at 13-14.7 at cruise, and will drop into the single digits when you open it up. I know with different carbs and different power valves, lower engine vacuum can cause the power valve to be fooled into opening too early, causing over-rich conditions. I wonder if there are any aftermarket Q-jet manifolds out there that work with E-heads? I've toyed with the idea of E-heads or KRE's for my '65, but if I can't run the stock intake, forget about it! I wish I could be of some help here....you surely don't need to go down the rabbit hole chasing ghosts, at this point. I would step back, take a breath, and then start making one single change at a time. If I had an aluminum Q-jet manifold, I'd send it to you. Hang in there, bro'.


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## tiretread (Sep 28, 2015)

Love it and keep posting!


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## BearGFR (Aug 25, 2008)

I relashed the valves earlier and bore-scoped a cylinder. I didn't see any scoring at least. Since I've been doing battle with the carb, I've changed the oil and filter 4 times to make sure it's not diluted. Each time I've smelled gas in it, not strong, but present.

Anyway, back to the story.

How to keep the idle from being crazy lean without making cruise crazy rich when the "motive force" that operates the applicable circuits in the carb in both cases is the same: manifold vacuum. I started studying on exactly how the idle and transfer circuits in these things work, and also reached out to the tech folks at AED and explained my problems, asking for their help. 

I figured out which passages in the main carburetor body feeds into the transfer slots and the idle ports, respectively. I identified a couple of spots "downstream" from the idle mixture screws and started trying to figure out a way to add restrictions at those points, thinking that my problems were mostly happening when the engine was starting to run on the transfer slots off idle, and manifold vacuum was coming up quickly. I found some examples of how others had done this using some small threaded inserts into the main body (first picture below) but I didn't have anything to do that with and I also wasn't ready to start making permanent modifications to the carburetor. So what I did was to cut some 3/4" pieces of .052" wire that I could insert into the passages that feed the transfer slots. The was no way for them to get loose and get sucked into the engine. This helped a little - but it wasn't enough to fix the problem when I tested it. I was getting ready to add more wire to restrict fuel more when I heard from AED. They understood the problem and suggested increasing the size of the idle air bleeds by quite a bit - jumping to .078 from .070. These bleeds add air into the fuel that goes to both the idle ports and the transfer slots to help emulsify it. The rationale was that adding more air would help lean things out in both circuits, but I should be able to open up the idle mixture screws enough to keep a good idle. This is one of the things that I'll have to admit is nice about working with a Brand H carb, at least the one I have. The idle air bleeds are screw in pieces that look like tiny main jets and are easy to change, unlike on most others where you either have to drill out a fixed orifice and hope you don't overdo it, or deal with a pressed in piece. 

The largest ones I had on hand were .075 so I put those in. I also had the idea of bumping up the idle speed a little bit to try to get it idling at a point where it's making a little more vacuum, so there wouldn't be such a big difference in vacuum off-idle, hopefully giving me a better chance at keeping the mixture in an acceptable range both at idle and just off-idle. I let it warm up, set the idle to about 1050-1000 in neutral, and then worked towards the best idle I could get at 850-900 rpm in gear. I was able to get 9 inches of manifold vacuum (highest so far) and a good mixture in the mid 14's.

This was a big improvement on the test drive. It still was tending to go rich just off idle but the swing wasn't nearly as bad as before. This made me think I was on the right track.

I went back to the shop, got out a pin vise and some wire drills, and opened up the bleeds to .078. The results were predicatble -- which in and of itself was a huge victory because up to this point nothing I'd tried was making sense. 

This is where I'm at right now. I'm going to open up the bleeds a little more, say to .084, and see what happens. 

To be continued...

Bear


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## geeteeohguy (Feb 2, 2008)

Great news, Rob! Remember, that a carb uses venturi vacuum going down the road, so it's not all manifold vacuum. The 1915 vintage Holley G on my '15 Ford will actually ice up due to venturi action even on a hot day, which is why these cars use a hot air tube to the intake port of the carb!


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## BearGFR (Aug 25, 2008)

I hate when that happens --- I had a nice long reply written and lost it somehow, now I have to start over.

Abridged version:
I opened the idle air bleeds up to .084, reset the idle, and took it out for a drive just now.

Settings:
Idle air bleeds: .084
Mixture Screws: 1 1/4 turns out
In gear Idle RPM: 850
In gear Idle vacuum: 10-10.5
In gear idle mixture: 14's-15's (at operating temperature)

Cruise is better. A/F readings at 40 mph are now in the upper 11's and kiss the 12's occasionally. 60 mph is in the 12's, sometimes 13's. I'm still blaming this on the extreme difference in idle vacuum with even small changes between say 850 and 1400 rpm. I could tighten things up some more with a faster idle (950 or so in gear) but that gives me an in-neutral idle of 1100 or better and causes it to occasionally diesel when I shut it down, and I don't like that. If idle drops into the 700's, vacuum drops with it to 8 or less and mixture shoots into super lean territory - 17's and up, even 20's. This may be as good as I can get it for now, but at least it's livable and I don't have to worry so much about damage from fuel wash.

If I roll into the throttle gently from 40 mph, enough to get into the main boosters but not enough to get into the secondaries, it's dang near perfect. High 13's, low 14's - and stays there until I go back to a steady cruise when it gets a little richer, but not by a ton. Right now my working theory on why a 60 mph cruise is leaner than a 40 mph cruise is because at 40 it's still running more (maybe even completely) on the transfer slots but at 60 the mains are at least partially working.

WOT is still fat. If I leave it in second gear and open it up from 40 mph, holding it there for 4 seconds, it stays in the high 10's the whole time and I can also see traces of black smoke in my mirror. This is making me think that either I need to jet it down some or go larger on the high speed air bleeds. David Vizard in his Holley book says that tuning the bleeds is most useful when you need to equalize the main circuit over the rpm range --- for example to correct a problem where it's lean at 2000 but rich at 5000. That's not my problem right now, so maybe the jetting is where I should start. I can't hold it at WOT for more than about 4 seconds from 40 mph because by then it's almost kissing 90 mph 

Bear


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## BearGFR (Aug 25, 2008)

Some photos that I hope will explain how the fuel travels through the carburetor and to the idle ports and transfer slots. These are in reverse order, starting with the feeds to the transfer slots and idle ports that are in the throttle plate.

Bear


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## BearGFR (Aug 25, 2008)

It's better still now. I disconnected the link to the secondaries so that I could focus on what the front half of the carb is doing. I jetted it down to 77's/87's (keeping the 10 number spread between primaries and secondaries even though I have the secondaries disabled at present).

Idle in gear is now at 950, mixture screws adjusted to yield 14's+ on the A/F meter with the engine warmed up. Cruise mixture is better - high 12's-13's and now "acceptable" but I still want it better. WOT is better too - running as a 2barrel like it is, it's in the high 11's now. My plans now are to go a little smaller on the jetting and also make some smaller idle feed restrictions. They're at .035 now. My targets are to get cruise A/F into the 13's-14's, WOT to around 12.5-13.2, and keep a 'decent' idle.

Bear


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## BearGFR (Aug 25, 2008)

Update:

I just got back from another test drive and it's now the best it has been so far.

My most recent changes:


Changed the idle feed restrictors from .035 down to .030. This I did by getting some #8-32 x 3/16 socket head set screws and drilling .030 holes into them. The .035 restrictors that originally came in the carburetor are #8-32 x 3/16 socket head brass screws. I couldn't find brass ones, but I did find some in stainless steel. Good enough. My reasoning for restricting the idle feed more was to reduce fuel flow to both the idle mixture screws and the transfer slots (these restrictors control both). I knew that I could compensate on the idle mixture screws simply by opening them more, however the flow to the transfer slots is not directly adjustable unless you do something like I just did.
Jetted both ends of the carburetor down. The primaries now have #75's, the secondaries now have #85's. The primary side has a power valve that opens below 4.5 inches of vacuum and adds additional fuel to richen things up, whereas the secondary side does not have a power valve and they're only active at or very close to WOT anyway - hence the reason for the size difference in jets end to end.

I warmed the car up and adjusted for a good 900 rpm idle in gear with an idle mixture in the 14's-15's. This AEM A/F meter is very responsive and shows instantaneous readings, so I watch it for several seconds to get a sense of an average mixture. It's not unusual to see it bouncing over a range from around 14.0 to 16.9 while sitting idling in gear.

As before, a 950 idle in gear equated to 1050 or so in neutral, with a corresponding slighly richer A/F mixture due to increased manifold vacuum pulling more fuel. However this time the 'swing' wasn't as pronounced due to the smaller idle feed restrictors. That's one of the effects I was hoping for. Also as expected I had to open the mixture screws quite a bit to get this new set point. Whereas before the best idle was with them opened 1 1/4 turns, now they're open 1 3/4 turns. I know that doesn't sound like a lot, but watching the A/F meter, even a change as small as 1/8th of a turn is enough to see a significant change on the meter. At the previous setting of 1 1/4 turns out with the new smaller idle feeds, it was so lean that the car wouldn't start and keep running.

Cruise. This is where the real success happened. I'm still running the car with the secondaries completely disconnected so I can focus on getting all the part throttle mixtures dialed in. At a steady 40 mph cruise I was seeing mixtures in the 15's and higher, whereas before they were in the 9's and 10s'. At a steady 60 mph, they're in the low to mid 14's. Dang near perfect for light/part throttle cruise. I was overjoyed at this result. Holding it at WOT for 3-4 seconds keeping it in second gear even running on only half the carburetor was 12.8 to 13.1 - also nearly perfect. It's a cool day here today with a lot of humidity, so I'm considering going back up one size on the jetting to 76/86 to richen it up a little, then using the high speed air bleeds for fine tuning. 

The accelerator pump settings are close also. Even running only on 2 barrels with the drag radials on, there's no hesitation when I hang my foot in it from 900 rpm and it breaks the tires loose easily.

I also have another A/F meter, a hand-held Innovate LM-2 and a bung for it in the passenger side exhaust. At some point I'll connect it up also so that I can read both 'sides' of the engine and make sure they're both seeing the mixtures that I want.

I think it's finally getting close to being right.

Bear


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## My65goat (Jul 26, 2017)

Your patience and attention to detail are impressive! I have really been enjoying your updates on this thread. Thanks for sharing!


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## geeteeohguy (Feb 2, 2008)

Agreed. Bear is quite a bit smarter (and a _whole_ lot more persistent) than the average bear, that's for sure! Great to see it coming together. Your wallet will thank you every time you pass a gas station!


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> Agreed. Bear is quite a bit smarter (and a _whole_ lot more persistent) than the average bear, that's for sure! Great to see it coming together. Your wallet will thank you every time you pass a gas station!


Aw shucks - thanks for the kind words :thumbsup:

I just got back from driving it "to town" (Fort Worth and back, about 45 minutes or so each direction.) Cruise mixtures at 40, 60 and 70 are in the "just fine" range - high 13's to even low 15's. Something that surprised me after installing this A/F meter --- how rapidly it changes and how far it swings when it does. I sort of expected it to stay relatively constant at least at a steady cruise, but it sure doesn't. 

I did richen it up a little from where it was last night - I went back to 76/86 on the jetting instead of 75/85, heeding all the warnings from all the smart people who write that being too rich (within reason) is much safer than being too lean, and engines will tolerate more of a deviation on the rich side without losing power than they will on the lean side. 

I also decided I was ready to reconnect the secondaries. I did try WOT a couple times with them reconnected, and as expected after the jet change it's richer than it was last night. Throttle response is very good, but I think can be better. 

Something "odd" that happened a couple times: easing into the throttle from a 50-60 mph cruise, not enough to really get into it but just enough to produce a moderate acceleration, it went very lean and developed a miss because of it. However, if I went "on down" on it and went to WOT it cleaned right up and started pulling. Weird... Another mystery to solve.

I have to go back to Fort Worth tomorrow and again Friday, maybe I'll drive it again.

Bear


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## 1968gto421 (Mar 28, 2014)

Bear, if you have been on the PY forum, you've probably seen posts by Ton Vaught and know that he's a retired Holley engineer. He did a huge thread not long ago on tuning and modifying Holley's. I found it really helpful. Here's the link for you.

SOME HOLLEY CARB TIPS - PY Online Forums

Hope you find it useful.

Also I have subscribed to your thread here as your info is always helpful.


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## BearGFR (Aug 25, 2008)

1968gto421 said:


> Bear, if you have been on the PY forum, you've probably seen posts by Ton Vaught and know that he's a retired Holley engineer. He did a huge thread not long ago on tuning and modifying Holley's. I found it really helpful. Here's the link for you.
> 
> SOME HOLLEY CARB TIPS - PY Online Forums
> 
> ...


Thanks for the tip and for the kind words. I've been reading through that thread - and oh my it's a long one. It seems to be about 60% "war story" with the balance begin actual tech info, but still there's a lot of good stuff there. Thanks.

Bear


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## BearGFR (Aug 25, 2008)

I've been talking back and forth with Tom Vaught and have started making some modifications to the carburetor that he recommended. I'm still working on it, but seeing improvement. It helps a lot to be in contact with someone who has a long history of dealing with these things and knows what changes have been made over the years, especially considering this is my very first experience with one. One big change that I didn't know about involves the location of the idle feed restriction. Apparently, originally it was located very close to the main metering jet at the entrance to the passages that feed into both the idle mixture screws and the transfer slots. However at some point, Holley (and others) chose to move the restriction some distance "down stream" which placed it after the idle air bleed, resulting it in having to meter emulsified fuel (fuel with air mixed in) as opposed to previously when it was metering liquid fuel only. I drilled and tapped threads into the original location so that I could 'move' the idle feed restrictions 'up stream' to the original locations, and it made a big change. Whereas before I was getting reasonable results with .031 restrictions located in the "emulsified fuel" location, now I'm getting better results with .035 restrictions in the "raw fuel/up stream" locations. It's making more idle vacuum now than it ever has with this cam: 11 inches in gear with a 930 RPM idle, 12+ in neutral at about 1000 RPM. Tom also suggested changing the holes in the metering block emulsion channels. Originally the blocks had 5 .028 holes in each channel, with holes #2 and #4 (numbering from the bottom of the channel) plugged. He suggested "swapping" that: plugging #1 , #3 , and #5 but leaving #2 and #4 open. I did that also. 

Those changes have made idle and low/light cruise a lot better than before. Part throttle acceleration (about half throttle, not getting into the secondaries at all) is now going lean enough that there's lean misfire present. WOT is still too rich. My plan for today is to jet it back up closer to where it was originally on the primary side (it has 76's right now so I'll go to 78's or maybe 80's, it originally came with 81's) and probably also jet it DOWN some on the secondaries, perhaps to 84's or less) and see if that doesn't both help the lean misfire condition on moderate acceleration and the richness at WOT.


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## geeteeohguy (Feb 2, 2008)

Thanks for the post, Bear. Really good information, and well explained. No disrespect to the _'Railroad_, but you're gonna have to change from "_BearGFR_" to "_BearAFR_" !


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## BearGFR (Aug 25, 2008)

Welp, THAT didn't work. I went back to 80's on the primaries, 84's on the secondaries, .038 idle feed restrictions... and it was almost back to where I started with the carb being too rich "everywhere". I guess I made too drastic a change.

So, right now it's running 78 primaries, 84 secondaries, and .035 idle feed restrictions. Cruise is better, but still a little bit on the fat side. Idle is decent. Half-throttle acceleration is just about right on which tells me that the 78's on the primary side are correct, or at least very close. WOT is also still fat. There's also a stumble if I just stomp on it from a stop - not a bad one, but it's there.

I think I just learned that I need to make smaller incremental changes (duh). My next move is going to be to go to .033 idle feed restrictions to try to improve cruise a little more. 

To try to address the too rich WOT mixture I'm going to turn my attention to the passages that feed fuel when the power valve opens. Right now they're at .062 and fixed. I'm going to have to take a deep breath, then drill and tap those passages so that I can insert 6-32 x 3/16 hex socket brass set screws that I will drill to various sizes hoping to find the correct WOT mixture.

For the 'stomp it' stumble I'm going to begin by putting a little more aggressive cam on the secondary side accelerator pump and see if that helps. It has .042 pump nozzles on both ends now which are pretty big, and the "blue" cam on the primary side which is just 1 step removed from the "biggest" one there is. To this point I haven't done anything to the secondary pump since taking the carb out of the box, so that's why I'm going to try there first.

I'm going to leave the jetting along for now.

Bear is nothing if not stubborn 

I think before this is all done I'm going to wish I'd gone ahead and bought that data logger to enable tracking mixtures over RPM over time. Watching the meter in the car, I've been a little surprised by how quickly the readings change and how widely they vary over very short time intervals. I have to watch it for more than just a few seconds to get a feeling for what the 'average' is, and doing that isn't very safe while driving 

Bear


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## geeteeohguy (Feb 2, 2008)

Bear, I've done this kind of emission testing on a dyno and can tell you for certain that you need to run the car at a set speed for at least 15-20 seconds for the tailpipe readings to calm down and stabilize......longer is even better. Very easy to do on a dyno, not so much on a public roadway. You might need to cave and buy some dyno time to get this thing ironed out. Or not....you _are _in Texas!


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## BearGFR (Aug 25, 2008)

Just got back from driving it to town and back, and it's better. At least now the changes I'm making are having results that are moving in the direction that I expect.

Current calibration:
Jetting: 78/84
Idle feed restrictions: .033
Power valve restrictions: .059 (10% smaller in area than the previous .062)

Idle is very good - highest vacuum yet at 15" in neutral and 1050 RPM (haven't checked it in gear yet because Mrs. Bear was rushing me to go to town 
Cruise mixtures are better - in the 12's once it gets warm but I'd like them to be leaner still.
Half throttle acceleration: 14's and 15's --- dang near perfect
WOT: improved at 11.2 (was 10.9) but still needs more improvement. Now that I have the channels opened up and tapped for threads, I just need to make some smaller restrictions.

I think I can get cruise leaner now by going larger on the idle air bleeds and without having to go smaller on the IFR's. The 'quality' of this idle is the best so far.

Accelerator pump tuning is the lowest priority right now.

I'll attach some photos of my modifications to the Power Valve Restriction Channels and the Idle Feed Restrictions.

Bear


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## BearGFR (Aug 25, 2008)

Just got back from another test drive after making some more SMALL changes. I think it's very close, maybe even "close enough"!


That is, except for the stumble when I stomp on it, but all things considered - where this thing is going to be running 99% of the time it's pretty darn good right now

Current calibration:

Idle Air Bleeds: .073 (up from .071 - this seems to have contributed to a leaner steady state cruise which is just what I was hoping for)
Main jets: 78/84 (no change)
Idle Feed Restrictions: .033 (no change)
Power Valve Channel Restrictions: .043 (down from .059 - was hoping to lean out WOT and this seems to have worked)
High Speed Air Bleeds: .031
Pump Nozzles: .042
Pump cam: Blue

Results:

Idle mixture in neutral: 12's
Idle mixture in gear: 13's
40 mph cruise mixture: 12's-13's <== Improvement
60 mph cruise mixture: 13's-14's <== Improvement
Half throttle acceleration: 13.5-14 
WOT: 12.2-12.3 <== Improvement!

I'd like to get the steady state cruise numbers just a little leaner, but if this is as good as it gets, I can live with this. Last item of business is to get rid of the stumble. I can go bigger still on the pump nozzles and there's one more pump cam "above" this one that's more aggressive. I found out earlier that the 50 cc pump, which is what this thing has on the secondary side, uses completely different cams from the primary side and I've not yet found out if there's a selection of cams for that pump or not.

(whew)

Bear


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## 1968gto421 (Mar 28, 2014)

Wow, Bear, you're getting into the skill area that Q-jet guys like Cliff Ruggles and Sean Murphy are in. Am glad Tom Vaught has been helpful to you, he does know his stuff.

Hope you can get this carb where it is totally where you want it. I am finding your write-ups to be a tutorial on working with Holleys. I have the Vizard book and others but your write-ups really cover how-to-do-it in the real world where you don't have a dyno and engineers helping you.

Thank you for posting all this and for your updates and the great photos.


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## PontiacJim (Dec 29, 2012)

You might want to take a look at your timing at this point. With the adjustments on the carb, it's possible you might need to dial in the distributor to match - which may get rid of that slight stumble. Tune Your Vacuum Advance for Better Drivability


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## BearGFR (Aug 25, 2008)

Timing is dead on - and vacuum advance is functional, connected to manifold vacuum (because this carb does not have a ported source) so it's active even at idle. Since the stumble only happens when I hammer it into the secondaries, I'm suspecting that I need a more aggressive cam on that side. That side is a 50cc pump so selection is limited - Holley only has 3 different 50cc pump cams. Right now it has the 'mildest' of the 3, so I have at least 2 more options to try. I might also try a larger nozzle on the secondary pump.

It's good everywhere else now, so this last item of business isn't a high priority.

Bear


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## geeteeohguy (Feb 2, 2008)

Great information, Rob. Thanks for posting it. Not easy getting a precise dial-in AFR wise and getting it as clean as that with all that camshaft. I've certainly never gone that sophisticated/refined on any of my old builds! Well done!


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## BearGFR (Aug 25, 2008)

I finally decided to tackle the last hurdle, which was getting the accelerator pump circuit dialed in so that there's no hesitation and throttle response is instant, no matter how much I "Flintstone" the loud pedal.

I could tell that it needed 'more' pump shot by watching my A/F meter, seeing that it was going extremely lean momentarily whenever I stepped on it "with exuberance". 

This was with the 'blue' pump cam on a 30 cc pump on the primaries, 50 cc pump with the brown cam on the secondaries, and 0.042 pump nozzles. 

I could have continued making small incremental changes and trying to "sneak up" on the proper calibration, but I decided to try a different approach: throw the kitchen sink at it and see it that's "too much", then work smaller/lesser from there.

So, I swapped out the front pump for the larger 50cc pump, went up to 0.046 pump nozzles, and also yellow pump cams on both ends. The yellow cams are the most aggressive ones available as far as I know. These cams come with only 1 hole for the mounting screw instead of the usual 2. I installed the bigger pump kit on the front along with the cam, but when I went to adjust the pump arm I could tell that in that orientation with my idle settings, the pump arm would already be part way up the cam ramp. That meant that I wouldn't get the full pump shot on that end. So, I made some marks and drilled another mounting hole in the front pump cam so that with the primary throttle at idle, the pump arm sits on the 'flat' part of the cam and also allows me to adjust the linkage so that as soon as the throttle moves any at all, it starts pumping fuel.

I took it out for a test drive.

Bingo! I can stomp on it from an idle and throttle response is instant. It lights the tires, immediately up-shifts to second, and keeps on spinning them all the way through second gear until it up-shifts to 3rd. Watching the A/F meter when I do that, it dips into 10's for a brief instant when the pump shot first hits but immediately goes back to the mid 12's at WOT while all the other excitement is going on.

I'm declaring a victory. :thumbsup:

Bear


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## My65goat (Jul 26, 2017)

I really enjoyed following this thread Bear. Congrats on your build and your super fine tuning!


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## 1968gto421 (Mar 28, 2014)

Congrats, Bear, you did it. I'll be saving your thread as THE Holley tutorial. Thanks for posting it all.


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## BearGFR (Aug 25, 2008)

More in the continuing saga...

The carb was a lot better, but still not what I wanted. The problem was cruise A/F ratio. It was staying pretty much in the mid 10's which is super rich, when what I wanted was upper 12's, 13's, maybe even low 14's. I got really discouraged about the whole thing (which is why I haven't written in a long time) and in fact haven't been working on the car or driving it any.
I got semi-motivated, and decided to try adding some transfer slot restrictors since they are what feeds most of the fuel during the time period when it's off-idle but not yet fully running on the main jets, main metering circuits. So I tapped the 4 holed in the carb main body and made some restrictors for those holes using some brass hex socket set screws. The locations for the restrictors you can see in this diagram.







Seemed like a reasonable approach, but in reality it made the car run like crap - everywhere. :crying::frown3: --- so I took them out, putting it back to where it was before at least.

Then I got to thinking, I know that the Idle Feed Restrictors control fuel flow to both the idle circuit (where the idle adjustment screws are) and the transfer circuit. For reference, the carb originally came with IFR's located here, but a Holley expert over on PY (Tom Vaught) I'd been getting help from told me that Holley had relocated them in the past in an effort to improve emissions, but it hadn't actually worked very well. He recommended moving them back to the original location. Here are a couple photos that show how the carb came, and how I relocated the IFR's on his advice.















It doesn't look like much of a change, but the significance is that with the IFR's in the "high" location, they're actually metering a mixture of air and fuel. However in the "low" location, they're submerged in liquid fuel and therefore do a much better, i.e. more accurate, job of controlling flow. You can see from the first diagram I posted that air doesn't get introduced into this flow until "after" the fuel has been metered whenever the IFR's have been relocated. 

Anyway, back to the saga. I figured I could restrict fuel flow to the transfer circuit by using smaller IFR's, but also figured that would require me to open up the idle circuit screws more than the recommended "1 to 1.5 turns" that most Holley experts recommend so I resisted that idea - for weeks. Then I had an epiphany: What does it really matter how far the screws have to be out, as long as I can get a decent idle mixture? Doh! :surprise::|
So I did. I made smaller IFR's that were down to "about" 0.025 from the 0.033 they had been. I say "about" because I just found out that I apparently neglected to record the actual new size in my spreadsheet I've been using to track all these changes (doh! again) so at some point I'll have to open it back up and measure.

Viola. Cruise A/F mixtures in the high 12's and occasionally low 13's without impacting things "anywhere else". Well, "almost". I've run out of adjustment on the idle mixture screws but the idle will still go too lean with this cam if RPM falls below about 950 rpm, but that I can live with a lot easier than I can a cruise that's so rich that I have to worry about raw fuel washing all the oil off the cylinder walls. I might try going just a teensy bit smaller on the idle air bleeds to see if that helps, but I won't keep those if it also impacts my cruise mixtures - which it very well might.

One thing I've learned from all this: People who talk about "how easy a Holley is to tune" must never have actually tried to get one "right" on a moderately hot street engine. It's very hard to get one of these operating with optimum A/F ratios in all modes of operation at the same time: idle, off-idle hard acceleration (bog-less), cruise, main jets, power valve enrichement, and WOT. Either they've not done it on an engine with a cam like this one (or even more radical), have never measure what their A/F ratios are in all the different modes, or maybe just tolerate it being badly "off" somewhere. QJets have a big advantage over these things due to their "on demand" CFM capabilities and the metering rod mechanisms that do a great job of adjusting fuel metering based on engine load. 

I'm really wishing that I could still use mine, but I convinced myself that I needed more CFM and also didn't really like the manifold I was having to use with it. I just hope I wasn't wrong... :surprise::frown3:

I'm still a little bit mystified as to why going with smaller IFR's has worked when adding the transfer slot restrictors was such a bust. About the only idea I've had on that one is that the t-slot restrictors, because of where they go, are having to try to meter a mixture of both air and fuel whereas the IFR's in their present location only have to deal with fuel.

Bear


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