[Motorhead]

I just finished putting a pair of 450 vacuum secondary Holleys on my Weiand Tunnel Ram on the 289. Runs pretty well for the stock tune, but I have a few questions:

1. The vacuum secondaries seem to be a little slow, both on the opening and especially on the closing. This is a 5-speed manual trans, and when I've got it wringed out and let off the gas for a quick shift, it feels like there's a shock absorber keeping my pedal from closing quickly. Looking at how the carbs operate, I think it's the vacuum canister taking too long to bleed off, holding the secondaries open which in turn holds the primaries open due to the linkage. It's not disasterous, but it gives me a feeling like I'm not in total control of the throttle. There is a tiny orifice in the top of the vacuum canister bottom-half, that I believe is responsible for controlling the rate that the canister can breath. I think the solution is to drill out this orifice slightly, like one drill bit size at a time, until I'm happier with the feel. Does this sound right?

2. The idle doesn't seem horribly stable. I can get it down to a rich 1000rpm idle, but if I try to go any lower it stumbles, leans out, and dies. The idle air bleeds are huge on the primary side, I think I may try putting a wire in them to choke them down a little and see if that helps. I'm wondering if the cure is to back out the secondary throttle stop screws a little? The problem with that is, they are both pretty well frozen into the carb base plates. Any suggestions how to get them un-stuck?

Anyways, any recommendations on tuning a dual-quad setup in general will be welcome. As mentioned it ran pretty strong, the secondaries may be opening a tad late, but maybe my above fix will help with that without adjusting the spring. There was also one time I floored it from about 2500rpm, it leaned way out (on my wideband O2 gauge), bumbled for about a second, and then like a light switch it pulled in rich and took off. Not sure what the lean out was about, might be I need more pump shot, but that's easy enough to avoid by not just mashing the pedal.

Thanks!

 

[DanH]

strong return sping . once the pri. are closed, the sec. are also. that's with no bent or . messed up links
a swap to the dual carb vacuum tops will help with even opening . can still buy them from some carb parts suppliers. A vacuum hose connects then together

overcome a lean , by not stomping the pedal ,,what fun is that ? fix it so you can

 

[Motorhead]

strong return sping . once the pri. are closed, the sec. are also. that's with no bent or . messed up links
a swap to the dual carb vacuum tops will help with even opening . can still buy them from some carb parts suppliers. A vacuum hose connects then together

overcome a lean , by not stomping the pedal ,,what fun is that ? fix it so you can

I currently have the spring in the throttle cable plus a return spring on the second carb (in case the linkage fails). The pedal already feels really heavy... Maybe its just been too long since I drove a non-EFI rig, but it feels like too much spring, don't really want to add much more.

I saw someone with the vac hose connecting the two. I don't think that would guarantee synch though, depends on If the springs and diaphram are perfectly matched. I think a better fix is to connect the secondary throttles mechanically with linkage, force the vac canisters to work in unison. Sure, they will fight a little, one will probably lead the other, but the net result is they still open in unison. Maybe there's something wrong with this plan, but I think it's a good idea...

Yes, the long term plan is definitely to fix the lean spot so I can flog it, but for now its close enough to go drag racing this weekend.

 

[Motorhead]

Ok, think I figured out the secondary closing thing, at least part of it. Took the canisters off, when I fully compressed them and let go, one was about twice as fast to extend as the other. Took the lid off, found the right size drill bit for the hole, and poked some crud out of the one on the second carb. While I had it apart, I did enlarge it one drill size, just to help a little more. Need to drive it again to get a feel for it now, but I think that problem is solved. Still appreciate any help on anything else like un-freezing the secondary throttle stop screws (or just drill and tap larger?) or any other wisdom you guys that have dual-quad experience can bestow on me.

Here's a couple pics. I bought the carbs off eBay, and the intake off Craigslist. They were all well seasoned, I cleaned them up, sandblasted and powdercoated the intake Silver + high gloss clear and the exterior of the fuel bowls and main body Dark Ford Blue, and brushed/sanded the edges of the metering blocks to make them shine.

Still need to make an air box (nothing I can buy will clear the firewall, and I don't want to cut it). Planning on a shaker kind of setup, but that will likely be a winter project.

 

[turbo2256b]

I would in your case send the carbs here Nickerson Performance Competition Carburetors, Marine, Automotive, Motorcycle and Personal Watercraft
One because they are used and dont know what has been done to them by the previous owner. Two because 2 carbs need to be made identical twins not faternal twins. No 2 of the same carb flow/meter the same without them being matched up.
I purchase the quick change secondary caps and install a tube for a hose between the 2 to equillize the vacuum between them. There are caps for this but not quick change. I also install allen head machine screws in the secondary idle stops i use them to adjust the idle once I have the primary transfer slot relation best as possible (can be tuff with duals and not alwas per the book). Idle will most often end up rich for them to react good off the line.

 

[KULTULZ]

I saw someone with the vac hose connecting the two. I don't think that would guarantee synch though, depends on If the springs and diaphram are perfectly matched.

I think a better fix is to connect the secondary throttles mechanically with linkage, force the vac canisters to work in unison. Sure, they will fight a little, one will probably lead the other, but the net result is they still open in unison. Maybe there's something wrong with this plan, but I think it's a good idea...

You cannot have both secondary opening by vacuum and mechanical linkage. The mechanical system will over ride and negate the vacuum feature. With mechanical secondary's, you would need to go to double pumper to prevent a/any momentary lag as the fuel catches up the to air flow (although mechanical can be done with a kit(s).

Holley Performance Products Pro Series Secondary Linkage 20-122

It is best (IMO), to tune the secondary's to open simultaneously by balancing the vacuum servos for a street engine. You would use mechanical throttle linkage to either have progressive primary opening or simultaneous opening of the primary's.

Of course, your interpretation and mileage may differ...

 

[Motorhead]

You cannot have both secondary opening by vacuum and mechanical linkage. The mechanical system will over ride and negate the vacuum feature. With mechanical secondary's, you would need to go to double pumper to prevent a/any momentary lag as the fuel catches up the to air flow (although mechanical can be done with a kit(s).

Holley Performance Products Pro Series Secondary Linkage*20-122

It is best (IMO), to tune the secondary's to open simultaneously by balancing the vacuum servos for a street engine. You would use mechanical throttle linkage to either have progressive primary opening or simultaneous opening of the primary's.

Of course, your interpretation and mileage may differ...

No sorry, I didn't mean mechanically link them to the primary, I mean mechanically link them to eachother. Vacuum canister is still the only thing pulling them open, just force the two carbs vacuum canisters to work together. Right now they are as close matched as possible (identical springs and orifices) without using a flow bench and bending your own springs, but I'll bet they still aren't perfectly synched, and never would be unless you link them together.

turbo2256b: While I'm not a professional, I'm not new to tuning Holley carbs. My last 650 double pumper I put a 750 main body on, tapped all the air bleeds and replaced them with brass set screws so I could adjust them, and learned quite a bit through that process. These carbs are from two different sources, but they are both 4548 list number, both have the same metering block number, and both looked as stock as could be. I checked all metering orifices to verify they are both identical. The only difference I found was one had a size larger secondary metering plate, but I matched them up by drilling out the smaller one (since it's tough to make them smaller). I think they are as close as humanely possible, at least close enough matched for my purposes.

 

[blkfrd]

Yes on #1...you can open that hole up quite a bit more. Weaker return spring too.

What are ya workin on? I saw the pics and am curious

 

[fordman460]

Cover-Diaphragm Housing

PART #: 20-73

Allows You To Change The Secondary Diaphragm Spring Without Disturbing The Diaphragm
Has Balance Tube For 2X4 bbl. Application

 

[Motorhead]

blkfrd: How much is "quite a bit more"? I don't want to go too much, I could see one end up with weird oscillations if you went too big (primary airflow picks up, sucks secondaries open, primary airflow decreases, secondaries close, repeat).

It's an '85 Ranger shortbed, I transplanted the 289 and T-5 into it about 10 years ago, and it's been my part-time project rig ever since.

fordman460: Thanks for looking that up! That would definitely simplify spring changes, and help with the balancing.

 

[blkfrd]

blkfrd: How much is "quite a bit more"? I don't want to go too much, I could see one end up with weird oscillations if you went too big (primary airflow picks up, sucks secondaries open, primary airflow decreases, secondaries close, repeat).

It's an '85 Ranger shortbed, I transplanted the 289 and T-5 into it about 10 years ago, and it's been my part-time project rig ever since.

fordman460: Thanks for looking that up! That would definitely simplify spring changes, and help with the balancing.

Im going from memory so dont quote me, but i'm thinking 1/16 to 5/64

By the way, did you lower the engine? The tunnel ram looks like you could get away with a moderate hood scoop. Looks darn good! :tup:

 

[Motorhead]

Im going from memory so dont quote me, but i'm thinking 1/16 to 5/64

By the way, did you lower the engine? The tunnel ram looks like you could get away with a moderate hood scoop. Looks darn good! :tup:

1/16th WOULD be quite a bit more... the stock size was about .028", and I bumped it up to .031" (about 1/32nd). I think I'll leave it there for now, see how it feels. I'm sure the crud I cleaned out of one was delaying the secondaries from coming in on that carb, so it will be interesting to see how the power feels now.

The Rangers didn't come with V8s, so I guess you could say I lowered it, into the engine bay with the cherry picker. It's actually not as low as it could be... I used James Duff V8 conversion motor mounts, which use the standard SBF motor mounts and plates that bolt to the crossmember. The plates push the engine up about 1" higher than it really needs to be to clear everything, but they work and 1" would not be enough for me to clear the hood, so I didn't bother trying to lower it. As-is, the front fuel bowl on the front carb will be just barely peeking out from the hole in the hood (once I put it back on).

I'm building a shaker style air box, will connect it via 4" hose to my air filter box that's down in the battery location. I didn't want to do ram air, or leave the carbs hanging out in the breeze, didn't like the idea of them getting bugs splattered on them. We'll see how it turns out, this is the best/easiest solution I could come up with given it's too close to the firewall for any typical filter setup, and I didn't want to do body work (a hole in the hood is the extent of my body experience).

 

[Motorhead]

So I've had some time to do a little tuning and order some parts, like jets and a pair of vacuum secondary spring kits. Going in 3rd or 4th gear at 2000-3000rpm, if I lay in to full throttle it leans way out and bumbles/stumbles up until about 4500-5000rpm, where it finally richens up and pulls hard. If I'm already up over 4000RPM and stomp on it no problem. I THINK the problem is the secondaries are starting to open too early, the engine doesn't want them until it's up to about 4500RPM. The weird thing is I have the 2nd heaviest spring in (the tall brown one)! Does this sound right? Seems like with 900CFM on a 289, it shouldn't even be using the secondaries much. I'm pretty sure the secondaries are pretty much wide open at 7000RPM, because of the delay/slow closing I mentioned earlier (that wouldn't happen if the secondaries were mostly shut). Comparing the stiffest spring (black) to the one I have now, they are pretty similar tension, I think the brown one actually has more initial pressure, just not as much fully-compressed pressure. So my fear is that the short black/stiffest spring will start opening even earlier, and will just open slower... but ultimately they are so similar I don't think it will make enough of a difference. The Holley instructions for the spring kit claims with the brown spring that the secondaries go full open at like 8500RPM on a 350 Chevy, that must be a 1500CFM carb they tested with, because my dual 450s are going wide open on my little 289 at less than 7000RPM!

I'm thinking that if I make the linkage to synchronize the secondaries between the two carbs, it would be really easy to hook a little extra spring on the bar, and add/remove additional spring tension really quick and easy, and with infinite adjustability. My only other possible explanation is that the secondaries are opening too slow, and their main circuits aren't able to get going until 4500RPM, which means they are just letting in raw air up until that point... but that should not happen if the secondary circuits are calibrated right, and I haven't messed with them at all.

Other than that I've got no good ideas. Does this sound like they are opening too quickly or not quickly enough? Has anyone ever seen a setup that required the stiffest spring? Does this seem like it would be one of them?

 

[DanH]

carb tuning ..... accel pump/cams , power valves , shooters . just double the fun getting it set upbalance the secondary by vacuum , will be easier. get the tops for shared vacuum

 

[Motorhead]

carb tuning ..... accel pump/cams , power valves , shooters . just double the fun getting it set upbalance the secondary by vacuum , will be easier. get the tops for shared vacuum

Yes, I definitely want to synch the secondaries, eliminate one more variable. However I don't think the quick change tops with the vacuum hose link is the best method, I still think a mechanical link between the two is the most precise way to synch them.

I'm pretty sure the power valve is good, because cruising in overdrive I can lay into the throttle a little and see it stage in rich, right around 13:1. Overall I think the primaries are pretty well dialed in.

Also, don't think its the accel pump, although I have considered swapping for a cam that has more shot in the 1/2 to full throttle range. I'm sure that would help cover up the problem some, but it lasts many seconds, which seems too long for an accel pump problem. Also I'm basically mashing the throttle from a light cruise so it should get a strong pump shot. It seems entirely RPM dependent, always cleans up at around 4500 RPM regardless of how long it took to get there.

 

[turbo2256b]

Go with the largest volume pump cam. Then work with squiter size. You have an intake that has very poor low RPM even into mid range driveabilty charicteristics (lazy air flow). Big heads make things worse. Small heads and the intake is way to large. The large volume pump will squirt longer the smaller the squiter is.
Maybe you think Holley went with the vacuum hose between the caps for the fun of it. It wont garinte sinking the opening but its a definite help.
If you dont want to spend bucks for new caps. The boss for the tube is on the caps. I drill them and JB Weld small tubes in them.

Two of the same Holley carbs can differ as much as 25% in metering due to production tollerances. Possibly the 450s might be a bit large and staging the secondars in one of the carbs to come in later might improve drivability.

 

[PSIG]

If it helps, Ive run several tunnel-ram setups on the street (one was my DD for years), and although they take twice the tweaking, they generally fall in line without issues. I would tune each section in stages. Most of mine are from years back with no WBO2, so it was old race-tune techniques.

First, I'd balance the primary and secondary blade stops by measurement to be sure they were even. For idle, I'd use the vac gauge to get it close with even needle turns. Then a contact thermometer to check each header tube for fuel distribution. I'd wire the secondaries shut and tune the primaries completely (big carbs), or to the rpm point the WOT vac went more than about 3" vac (small carbs). This also tells me where I need the secondaries to come-in. <---

Note, the secondary blade stops will influence your idle adjustments. They need to be open a hair (as factory) but you may have to adjust them to 1/2 hair. This will give you more adjustability with your primaries as all the idle air won't be coming through the other 4 holes.

A secondary balance rod shouldn't really be necessary, but it both ensures even opening (and closing) always, and as a failsafe to keep distribution correct if you clog a vac releif or something on one carb. Not necessary, but nice to have. You can balance the secondaries with a small linkage rod and Heims between the arms the vac canister rods are attached to (there's room down on that side). A small added tab on each, facing down and 45° forward does it. I added the tab and a tack weld for security, then drill for the small machine screw to mount the Heim joint.

Un-wire the secondaries and make runs watching the vac gauge. I started with strong springs and went weaker until the vac drop started to go away. This would give a smooth transition and maintained best torque. Then I would tune the secondary fuel. It should be about done at that point.

David

 

[Motorhead]

Go with the largest volume pump cam. Then work with squiter size. You have an intake that has very poor low RPM even into mid range driveabilty charicteristics (lazy air flow). Big heads make things worse. Small heads and the intake is way to large. The large volume pump will squirt longer the smaller the squiter is.
Maybe you think Holley went with the vacuum hose between the caps for the fun of it. It wont garinte sinking the opening but its a definite help.
If you dont want to spend bucks for new caps. The boss for the tube is on the caps. I drill them and JB Weld small tubes in them.

Two of the same Holley carbs can differ as much as 25% in metering due to production tollerances. Possibly the 450s might be a bit large and staging the secondars in one of the carbs to come in later might improve drivability.

The driveability is actually very good, every bit as good as the low-rise single plane I had before. The only issue is when I stomp the pedal to the floor at anything below 4500RPM. The fact that I can floor it above 4500 without a stumble tells me the pump shot is not too far off. A bigger pump shot would cover up the issue, but could also cause a rich bog when I floor it at higher RPM. Looking at my data, the AFR does spike rich before it swings lean, both at low and high RPM, so I think you're right in that I should try smaller shooters. As a possible alternative, I may replace the pump arm springs with lighter springs, should have a similar affect as smaller shooters, and it's something I can do right now without waiting for parts. Also I am thinking about trying the pink pump cam, it has a little bit bigger overall shot, but the main reason is the shot is spread across the whole throttle range, it doesn't blow the whole shot in the first 1/2 throttle movement like most of the cams. Normal driving, the pump shot seems a little excessive (going by the WBO2 gauge), seems since I don't have a secondary pump shot, so I think having some pump in the top half of the throttle range would be beneficial.

I don't know why Holley offers only the vacuum synch and not a linkage kit, maybe because there are too many combinations of seconary linkage attachment and positioning of carbs; are the carbs side or front facing, is it a cross ram or a tunnel ram, distance between carbs... the vacuum link is a single kit that can be applied to all dual-carb geometries, a mechanical link not so much. Other than being universal, I don't see any way that the vacuum link would be better than a mechanical link, maybe you do?

And yes it's nice to save money, but I'm planning on having this setup for a long time, so spending $50 is not the problem. I think there are many benefits to the mechanical linkage, and once they are mechanically linked the vacuum synch doesn't really matter. One added benefit of the mechanical link is I can stick light springs in the canisters, and then use springs to the link bar to adjust the amount of spring with very fine granularity (adjust initial pressure and spring rate), much more than just the 7 springs the kit comes with (which have fixed rate and initial pressure), without taking apart the canisters ever again. Also I don't have to ditch my nice powder coated caps for plastic caps that may crack or leak eventually.

25% difference in metering sounds excessive, I would say that's more than just manufacturing tolerance, that's manufacturing error. I do understand manufacturing tolerance, I am an engineer and deal with it all the time. I have checked all the metering orifices, they are all exactly the same, or at least as exact as can be measured, so I'd say that's easily within 5%. There are undoubtedly other factors that can affect the metering, but ultimately I can't justify sending the carbs off to someone and spending probably $500+ hoping to get that last 2% of the tune, especially when there may be absolutely nothing to gain, I have other places to put my money.

 

[Motorhead]

Thanks PSIG, the Holley rebuilt kit instructions said I think 1/4 turn from fully closed on the secondary blades, and that's where I have them. With them at this point, and with the primaries matched, I get a good idle speed with about .020-.030" of the transfer slot exposed, and the distributor (ported) vacuum port just barely fully covered, so I think the blades are pretty close to right.

On the idle circuit though, I will note some things I think are odd. For the life of me I can't find an idle feed restrictor in the primary metering block. The only place it can be is in the idle well, where you'd have to remove the plug on top to get at it (which I'm not about to do). I think I'm OK without having to tweak it, but it does like to idle with all four screws at 1/2-3/4 turn open, which about half what you usually expect. My guess is that the idle circuit is purely vacuum driven (not airflow), and since I have two carbs, I have twice as many primary/secondary idle circuits feeding fuel, so it's richer than it would be with a single carb, thus the primary idle screws only need half as much opening (roughly). This may make the even cylinders idle leaner than the odd cylinders if the secondary idle circuit is feeding it's full amount, but I don't think I care enough to mess with it, since it idles good, light cruise mixture is good, and I don't see fluttering on the AFR gauge that can indicate distribution problems (I have a bar-graph gauge which is very responsive, and the laptop gives me slower response but more precise AFR when I am logging).

I've considered wiring the secondaries shut just to confirm that's where the problem is, would probably be worth the time to just do it, and that will also let me confirm the primary jetting is right where it needs to be.

What you've described for the secondary linkage is pretty much exactly what I have planned, except without welding. I plan to make a metal plate that will stack on top of the existing plate, will have two holes, one for the screw and the other to slip over the vacuum rod post for positive location, but be thin enough to not interfere with the vacuum rod. Then as you said, the link arm hanging down at 45 degrees forward so it swings over center, and probably about 1" long should be enough to minimize slop. It'll be close to the tunnel ram plenum, I'll probably have to bend it outward some for the screw/post/nut/whatever to clear. Maybe just welding a tab onto the existing piece would be quicker/easier, I just try to avoid permanent modifications to parts that are not easy to find replacements.

 

[PSIG]

What you've described is pretty much exactly what I have planned, except without welding. I plan to make a metal tab that will stack on top of the existing tab, will have two holes one for the screw and the other to slip over the vacuum arm post for positive location. Then as you said, the link arm hanging down at 45 degrees forward so it swings over center, and probably about 1" long should hopefully minimize slop. It'll be close to the tunnel ram plenum, I'll probably have to bend it outward some for the screw/post/nut/whatever to clear. Maybe just welding a tab onto the existing piece would be quicker/easier, I just try to avoid permanent modifications to parts that are not easy to find replacements.

The welding was just a tack, to effectively stake it from moving. Any movement negates the purpose, and a tack is simple and quick to cut away to change later if wanted. A 3/32 or 1/8 hole through the tab and arm with a short roll pin to positively locate would do the same. Whatever works for you. Your second spring off the secondary arm (probably front 2ndary shaft arm towards rear) is exactly the same method I've used to tweak external turbo wastegate actuators. Same mechanism. Use a light spring and add external to adjust. To fine-tune the spring, you can use a coupler nut like a turnbuckle off your anchor, an anchor tab with multiple holes, or for cheap 'n quick tuning experiments, I'd gather some coils together under a zip-tie. The tighter you zip it, the stronger the spring tension.
:tup:
David