Holley Carb Tuning Help

[JLeather]

Who on here is good with Holley carbs? Need some help diagnosing what may be one or two unrelated issues on my '67 D200. It's got a stock 318 with closed-chamber heads at ~9:1 compression, an Edelbrock LD4B intake, and I'm running an aftermarket small-cap vac-advance distributor firing an HEI and a 570 Holley "Street Avenger" although the issue I'm running into is pretty typical of any 4160-based carb I think. I'm fighting a hesitation off-idle when you punch it which is something I've worked through before with accelerator pump changes. If you roll into the throttle the truck is completely fine, but if you punch it (either from a dead stop or even while cruising 60mph+) it coughs and hesitates bad before taking off. The hesitation is worse when it's cold, so my inclination is not enough accelerator pump shot, but but before I go that route I wanted to make sure it isn't tied to my other problem.

The truck is a stick-shift, so I've got it tuned to idle about 750 rpm. 10° initial advance, about another 12° at idle from the vacuum can since it's hooked up to manifold vacuum. I think the carb is on the edge of being too big because I had to completely close the rear idle screws and it's only got the fronts open ~3/4 turn (when I tried to adjust it as a 4-corner idle all the screws were open less than 1/2 turn all around). The truck has an aftermarket p/s setup which provides some significant drag at idle when maneuvering into a parking space for instance and it'll drop the idle by about 200 rpms, even more on a surface like hot sticky asphalt. I would liken this to the same issue you'd have going from park to drive except I can't tell since the truck is a stick. Is it possible my idle rpm drop and my stumble off idle are actually the same issue? I don't want to go chasing the squirter tuning only to find out later that it was some other issue causing both problems? I've never tuned a carb with p/s before and it's messing with my head since it's not a consistent load. Some reading has suggested that I'm relying too much on the vac advance for idle and that's why it's dropping out under the p/s load, but since I'm not giving it any throttle the vacuum stays about the same when the idle drops. Nonetheless is this an application where ported-vacuum would be better? I suspect both my idle stability issue, my hesitation, and the fact that my idle screws are so far in might all be related somehow? PS the primary transfer ports are not excessively open and the secondaries are completely closed at idle; no secondary transfer showing at all.

[dbolterII]

Howdy, I'm no Holley expert so don't listen to me... I would start with a vacuum gauge and hope to see 17~20 "inches of vacuume".

The four corner idle circuits are then adjusted for max vaccume and highest idle RPM.

your vaccume @ idle dictates your power valve size... vaccume number divided by 2 is what size power valve you should have I.E.

20 vaccume = #10 power valve 15 vaccume = 7.5 power valve and so forth or the closest PV size available

also as you mentioned experiment with bumping up your accelerator pump discharge nozzle size

and lastly experiment with your accelerator pump cam easily interchangeable....

A lot of good Holley info on their website and you tube ....

best of luck ~d

[Wildergarten]

I've never seen a vacuum secondary Holley with dual metering blocks and four idle mix screws. Does the secondary block have a power valve too? I just don't see why they'd need an idle circuit in that side at all.

I had a 650 square bore double pumper on a 318 that I had modified to take a vacuum secondary diaphragm chamber (blew off the seconday accelerator pump). I'd call 650 a touch big for that motor, but with enough spring on the secondaries to keep the velocity up, my old D270 Dart Wagon with the A833 into a 2.93 8-3/4 was just a killer (a 911SC was my favorite prey, especially with the GF in the car). How that car didn't get me killed I'll never know. I did use the dual stage power valve on the primary side and that did help once I'd played with jetting for months. Effectively, without a vacuum gauge it's hard to know which circuit in the carb is starving the motor. I had one in the dash.

What I can say about that carb is that clean fuel was an absolute must. The slightest piece of grit in the metering block would produce exactly the kind of behavior you are describing when the emulsion tubes weren't working just right. Cleaning the block even in perchloroethylene was of dubious value; usually it took a new one to fix the problem.

[martincom]

I encountered near the same symptoms with the D100 I acquired this spring. It is a 1971, 318, automatic. A previous owner had installed an Edelbrock Performer (spread bore capable) intake an a Carter AVS from a '71 non- high performance 440. It had a pronounced hesitation from idle, rich smelling exhaust, and the the idle mixture screws would have to be three to four turns open for best idle, but even at that, would hesitate. My first reaction was it was too much carb (600cfm) and it couldn't create enough vacuum at the idle ports due to normal air bypass around the perimeter of the throttle plates. Thus, why the idle mixture screws had to be open excessively. I was reluctant to shell out $600 for a new carb, the correct size, and would have preferred to return to the stock 2 bbl Carter Ball & Ball, but I had nothing on-hand and sourcing all the parts would have exceeded the $600 for a new carb.

So out of denial, I did put a kit in the Carter AVS. I did find one of the primary air bleeds was plugged. While the idle improved, the hesitation was still there. While I knew I was spinning my wheels and in more self denial about having to replace the carb, I did experiment with different accelerator pump settings---all to no avail. I had also done the preliminary vacuum measurements and check for vacuum leaks: PCV valve, brake booster, carb base, etc

So I finally ponied up an order a replacement carb. I went with a 4160 Holley, the smallest I could find, 390 cfm. I gave some consideration to the Street Demon, as the smaller primaries would have good throttle response, but I felt the secondaries would just drown a 318.

I was very pleased with the outcome. The hesitation is gone. Throttle response is excellent. No stinky rich idle exhaust fumes. I did some basic sparkplug read road tests (shutting down the engine at a number of speeds) and the out-of-the-box configuration appeared ideal. I haven't ponied up for an oxygen meter, which would provide a more accurate indication, but I'm comfortable with the out-of-box configuration.

In addition to the carb, the installation required Holley's throttle lever addition for Mopar applications and I did order a 340 throttle cable/kickdown linkage bracket to provide the correct cable/linkage geometry. I don't think the 2 barrel bracket would even work with the Holley and would definitely not yield a full opening of the throttle plates.

I do utilize ported vacuum to the distributor. You're probably overly advanced utilizing manifold vacuum. My basic timing is also 10 degrees.

[Wildergarten]

So I finally ponied up an order a replacement carb. I went with a 4160 Holley, the smallest I could find, 390 cfm. I gave some consideration to the Street Demon, as the smaller primaries would have good throttle response, but I felt the secondaries would just drown a 318.

With a spring kit for control of the vacuum secondaries, this simply isn't possible.

[martincom]

Yes, I suppose I should have elaborated. I doubt a 318, especially in a truck, is going to create any large amounts of cfm. So if the secondaries begin to open, it won't be much. As there are only feed tubes in the secondaries and no booster venturies, the fuel is just going to "glop" out of the feed tubes with little and poor atomization. The drowning I was referring to.

[Wildergarten]

Yes, I suppose I should have elaborated. I doubt a 318, especially in a truck, is going to create any large amounts of cfm. So if the secondaries begin to open, it won't be much. As there are only feed tubes in the secondaries and no booster venturies, the fuel is just going to "glop" out of the feed tubes with little and poor atomization. The drowning I was referring to.

This simply doesn't resemble what the 600cfm Holley on my old 3-speed Dart would do to a Porsche 911 (unless it was a Turbo Carerra). Ild slow to 45mph just to wait for them to appear in the rear view mirror. It would do 105 in 3rd gear. I never did top it out in 4th. The car usually got 15-19mpg depending :-) Towing its full weight it would blow over Sepulveda Pass or over the Grapevine with no effort at all. But I did spend a year tuning it, with extra power valves in back, a vacuum gauge in the dash, and a kit that allowed me to change main jets with the engine running. It was a lot of fun dialing that carb in, and modifying the double pumper for vacuum secondaries was even better.

[JLeather]

I've never seen a vacuum secondary Holley with dual metering blocks and four idle mix screws. Does the secondary block have a power valve too? I just don't see why they'd need an idle circuit in that side at all.

I had a 650 square bore double pumper on a 318 that I had modified to take a vacuum secondary diaphragm chamber (blew off the seconday accelerator pump). I'd call 650 a touch big for that motor, but with enough spring on the secondaries to keep the velocity up, my old D270 Dart Wagon with the A833 into a 2.93 8-3/4 was just a killer (a 911SC was my favorite prey, especially with the GF in the car). How that car didn't get me killed I'll never know. I did use the dual stage power valve on the primary side and that did help once I'd played with jetting for months. Effectively, without a vacuum gauge it's hard to know which circuit in the carb is starving the motor. I had one in the dash.

What I can say about that carb is that clean fuel was an absolute must. The slightest piece of grit in the metering block would produce exactly the kind of behavior you are describing when the emulsion tubes weren't working just right. Cleaning the block even in perchloroethylene was of dubious value; usually it took a new one to fix the problem.

Here's the specs on the carb:

https://www.holley.com/products/fuel_sy ... ts/0-80570

Only a PV in the primary side, but idle screws and discharge ports in all 4 barrels. I think I'm onto something with my PCV setup. The aftermarket PCV has way too much idle air bypass. I'm dropping almost 250 rpms when I plug the PCV. I've plumbed in a stock 318 PCV instead at least temporarily and retuned the idle and it seems much better. Haven't been able to test drive it because I stripped out of the ports on the rear axle brake splitter and it turns out Dodge is super weird (what the hell is a 7/16"-20 fitting?). Test drive coming sometime this week for sure. Might not have fixed my off-idle driving stumble but my static-steering performance is much better.

[Wildergarten]

https://www.holley.com/products/fuel_sy ... ts/0-80570
Only a PV in the primary side, but idle screws and discharge ports in all 4 barrels.

I was thinking, "That's just weird, simply because the linkage would need another idle screw for air which makes balancing it much more complicated." But now that I can see it, what they did was to set up the idle linkage so that it tips both sets of plates. I'd bet it's more uniform for smog and efficiency purposes. I like the gold anodize coating better than the bright finish. The former requires more process control, but the bolt threads last longer and don't gall as much with repeated use.

Haven't been able to test drive it because I stripped out of the ports on the rear axle brake splitter and it turns out Dodge is super weird (what the hell is a 7/16"-20 fitting?).

Yup, it's a bolt thread. In fact, when sandblasting, I put a bolt in that hole instead of the breather and left it there for the duration until the truck is done. I may just go get a 7/16 UNF bolt, tack a nut on it, and then drill and turn a barb on it for a hose.

I think I'm onto something with my PCV setup. The aftermarket PCV has way too much idle air bypass. I'm dropping almost 250 rpms when I plug the PCV. I've plumbed in a stock 318 PCV instead at least temporarily and retuned the idle and it seems much better. Test drive coming sometime this week for sure. Might not have fixed my off-idle driving stumble but my static-steering performance is much better.

Agreed, I think you've got the bulk of it.

[martincom]

This simply doesn't resemble what the 600cfm Holley on my old 3-speed Dart would do to a Porsche 911 (unless it was a Turbo Carerra).

Your Dart was a 318? I had a '69 Dart convertible with a 383. It was fast, all motor and little car. It was rather miserable to work on. Just changing spark plugs was a real chore.

Holleys have booster venturies in their secondaries. The Carter AVS, Thermoquad, Rochester Quadrajet, and others do not--just brass feed tubes. So the fuel atomization is far superior with a Holley, in my opinion. Carters were much less money than Holleys and why Chrysler utilized them. Dollar and cents on the bottom line. Chrysler switched to Holleys in 1969---not because they were less money or they had a marketable performance improvement. Carter had a labor strike and was unable to supply carburetors.

Holleys typically have idle mixture screws for the secondaries. Albeit, often not readily accessible and often require removal of the carburetor to do so. The 4160 I just installed falls into that category. I have several cars with 440 6-packs. The outboard carburetors also have idle mixture screw in the front of the throttle body. So you have to remove the rear carb to access them. It is a trial and error process and even an 1/8 of a turn makes a significant difference. Throttle plates never close air tight---there is always some leakage. Have an idle circuit allows that leakage to be a fuel/air mix---rather than just air. Which, in my opinion, yields a smoother idle and better off-idle throttle response.

[Wildergarten]

Your Dart was a 318? I had a '69 Dart convertible with a 383. It was fast, all motor and little car. It was rather miserable to work on. Just changing spark plugs was a real chore.

Yup, a '64 with a junkyard motor.

So the fuel atomization is far superior with a Holley, in my opinion.

Agreed. I also like the defined stages of jets and power valves that make using a vacuum gauge more profitable. Tweaking needles (basically oriface pins) in Carters or Edelbrocks is just too imprecise and unrepeatable, nor do they center in the jets with stability. They are easier to clean out than the emulsion tubes in the Holley metering block and therefore are much cheaper to tweak.

Holleys typically have idle mixture screws for the secondaries.

Mine never did.

The 4160 I just installed falls into that category. I have several cars with 440 6-packs.

You have my envy. Awesome induction systems, but they do take time. Too rich for my blood when I was a kid.

Always wanted a 340/6 Pack and to take that '64 hood and raise it to take the high pressure air off the glass. I started a second car I never finished. Both '64s had flared fenders and air dams. The treatment got rid of that goo-goo eyed look the original design had. With the stainless air deflectors for the back window of the wagon body, it was a handsome car. It had the 11" disc brakes and the last set of Velvetouch linings in LA; all aircraft grade stainless brakelines. A 1-1/4" sway with adjustable links on the front, with a 1" sway in the rear too. It had the top A-arms modified to give it more negative camber with the adjustable Moog ball joints. I made an A-frame for the 8-3/4 rear axle with a spherical joint at the bottom as a lateral location and anti-wind up device (polyurethane bushings and all). I also got rid of that stupid gas tank inlet by putting it atop the rear quarter above the tail light, complete with a drain and vent line, all electroless nickel plated. 8-speaker sound system too, most of them Altec. The 340 I had for it was ripped off while I was living in LA. Never finished the car.

When I moved back home to the Bay Area where I am now, with an international engineering career, building a house and dropping two kids, the car body and suspension just sat under a tarp. My beautiful blue metallic paintjob got rust blisters from the inside. It was so far from street legal it was too much of a liability to sell. So I pancaked the whole thing having too much to lose.

Sigh.

The outboard carburetors also have idle mixture screw in the front of the throttle body. So you have to remove the rear carb to access them. It is a trial and error process and even an 1/8 of a turn makes a significant difference. Throttle plates never close air tight---there is always some leakage. Have an idle circuit allows that leakage to be a fuel/air mix---rather than just air. Which, in my opinion, yields a smoother idle and better off-idle throttle response.

Touchy idle mixtures are a Holley trademark all right, and you're right about its importance in taking that initial vacuum drop without a bog. I never was seriously into drag performance though. I was after a station wagon blowing away the sports cars on a winding open freeway. To me that was more fun. On the east side of San Francisco Bay we have Highway 24, which winds its way through the hills with turns that were a challenge through traffic at over 100. When slowing down so that the vanquished could catch up, there was always one phrase discernable from their lips, "What's IN that thing???" I was a danger to the public, never a tailgater and very smooth about it, but definitely a source of general freakout. I get my thrills these days climbing trees with a chainsaw (including redwoods). Some things never change.

[PwrWgnDrvr]

....On the east side of San Francisco Bay we have Highway 24, which winds its way through the hills with turns that were a challenge through traffic at over 100.....but definitely a source of general freakout.....

24 is a mile from my house. Drive it almost daily for the last 50 yrs.
105 mph in THIS is a huge freakout!:

[Hobcobble]

....On the east side of San Francisco Bay we have Highway 24, which winds its way through the hills with turns that were a challenge through traffic at over 100.....but definitely a source of general freakout.....

24 is a mile from my house. Drive it almost daily for the last 50 yrs.
105 mph in THIS is a huge freakout!:
truck.jpg

That W300 would've worked great in the 1971 movie, Duel.

John

[Wildergarten]

105 mph in THIS is a huge freakout!:

When all is said and done, I'd have rather had a W300 cuz I think they look cool, but for the fact that I started with a flatbed made for a W200 I am NOT going to restructure for the difference in frame spacing. Sure would have liked to have had duals in the back for dumping loads.

Got a photo of the Green Truck today with a moderate load, and the frame is sagging. That's why I stiffened the frame for the new W200 truck with rear overloads and added the stiffer front axle.

[Hobcobble]

I've always liked that green W200. I saw it years ago at Terry's.

John

[Wildergarten]

I've always liked that green W200. I saw it years ago at Terry's.

John

Pine Green is a great color on that truck. I've had an ongoing debate in my head whether I want to do the new one with white grille, wheels, cab, and underbody boxes, or the black accent military look. Black is a lot easier from a project management perspective but I also DON'T want a white cab with an expanded metal rack over the top, as that would collect leaf trash that would drip tannins onto white paint in a grid pattern of algae I can just see on my new truck cab. Not good. Algae on Pine Green, not so bad until I can get to washing it off... Note to self: Work truck, work truck, work truck... but, but, but... I wanted a nice work truck, for once. It's maddening being me

That particular truck of Terry's had a lot of obvious problems from having sat so long in salt-spray Pacifica. The gas tanks in the bed need to be boiled out so I put one back in the cab and left the rest. The body has metasticizing skin cancer on one side. The tailgate is on its last legs (have an aftermarket one that needs paint). I've added a diamond tread rear bumper and a 10K# frame hitch. The carb had seen a fair bit of water. The brake and clutch hydraulics were shot. There was a quarter inch of oil impregnated with dust all over the bottom (no telling yet where that came from). The exhaust system had to be totally replaced. Replaced the distributor. There was no oil pressure switch on the electric fuel pump. Windshield gasket leaked like a seive (I've got one). Locks don't work...

Since getting it running, it's been a process of "discovery." The carb still has issues (could be low float level). I suspect the cam is trashed (from the lack of ZDDP in the oil). From what I heard today, I think the bed is coming loose somewhere. Headlight switch has gremlins. The starter occasionally refuses to engage the solenoid (relay's fine for now... worked today anyway). Fuel gauge died. The driver's side exhaust pipe broke it's hangars on one side (second time, because of our crappy county roads). Dirveline's OK so far, so that's the good news. Gotta keep the rats out of it though. Trapped two so far.

So it's an ongoing and going on and on sort of thing while I'm busy trying to work on else. This truck is for work that HAS to be done. It loaded out the last cord of firewood today from a job taking 16 trees out of the draw to the left in the photo. So at least it's doing its job despite the occasional fits, but it's not particularly reliable yet. Hopefully, with another year or so I'll have it mostly sorted out so that I can sell it in good conscience when the new truck is up and running... How come they don't have an emoji for prayer?

[Hobcobble]

That particular truck of Terry's had a lot of obvious problems from having sat so long in salt-spray Pacifica. The gas tanks in the bed need to be boiled out so I put one back in the cab and left the rest. The body has metasticizing skin cancer on one side. The tailgate is on its last legs (have an aftermarket one that needs paint). I've added a diamond tread rear bumper and a 10K# frame hitch. The carb had seen a fair bit of water. The brake and clutch hydraulics were shot. There was a quarter inch of oil impregnated with dust all over the bottom (no telling yet where that came from). The exhaust system had to be totally replaced. Replaced the distributor. There was no oil pressure switch on the electric fuel pump. Windshield gasket leaked like a seive (I've got one). Locks don't work...

So, in other words, the truck was in average shape. You did well
on this truck.

You wouldn't want to know what us guys in the N.E. rust belt have
to deal with. I could show you graphic pictures of decay.... but I
don't think you could handle it.

John

[Hobcobble]

Forgot to mention.....

Let me know when you're ready to sell it
in good conscience.

John

[nutz]

just a thought
had a 69 dart 273 the exhaust cross over on intake was clogged. it had a horrible hesitation until i cleared it out
some didn't put the block off plate in the cross over on your intake ??

[Wildergarten]

So, in other words, the truck was in average shape. You did well on this truck.

Did a lot better on the D200. At only $1200, I'll actually cover my costs in parting it out.

You wouldn't want to know what us guys in the N.E. rust belt have to deal with. I could show you graphic pictures of decay.... but I don't think you could handle it.

You haven't lived until you've worked in a bilge on a crappy old wooden fishing boat with leaking hydraulics in a space so tight you have to exhale to move. I did fully restore a 32-foot Sheldon cruiser that had been sold for $600 after it was floated off the bottom. That only took eight years. So you're right that I don't have time for one of those Rust-Beltin' lovelies, but I've been East-thither many times (in rural Illinois only a week ago). Frankly, the rusted vehicle scape looked better back there than it did during the '70s and '80s. But West Cost salt spray is not to be discounted. That Green Truck has an open gap down the side two feet long, the cowling is rotted, the trim is falling off, and the hood... well, let's just say I switched that out in the name of safety. Didn't want it catching too much air. Might have spoiled the view.