So I've been driving my newly built slant for a few thousand miles now, and it's time to get the carb dialed in. It ran 18.2 at mason dixon, and is getting sub-15mpg, leaving me to believe I'm leaving some on the table. This is my daily driver and I make a lot of 500mi round trip, 75+mph trips on the interstate, so I've tried to set it up for such.

Symptoms: Bog when quickly opening the throttle, and during normal driving from ~1500-~1900 rpm, noticeable when hot but enough to almost stall the car when cold. Too much pump shot maybe?

Pulled apart the carb to check the setup, got it secondhand from another forum member but haven't dialed it in for my car yet:
Holley 8007 vac secondary
Primary Jets stamped 512
#28 pump nozzle, cam on 2 notch
stock metering plate
4.5" PV

Engine/car setup:
High 9s static CR (.100 off the head, .170 in the hole, pings like crazy without premium)
Stock head valves & ports
MP .460" purple cam, makes 11-13" idling in gear (depending on idle speed setting)
6-1 headers, clifford intake
Stock converter, 904
2.76 open rear, 27" tires (highway screamer)


Anyway I have a secondary spring set and a secondary metering block on order. The other threads I've been able to find have advice for lumpier cams, higher rear ratios, etc., so that's why I've created yet another holley 390 topic. Apologies in advance if there's a thread covering this elsewhere.

Any tips/thoughts/comments on my setup? Going to try and start with a green spring and 52 jets in the secondaries, go up to a 6.5"PV, and back off the squirter to a #25 or so.

Thanks in advance!

What distributor are you running?
What is the initial timing set at?
How much mechanical?
How much vacuum advance?

Pretty tall tires.....I thought I was bad....

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Distributor from a '77, recurved with bigslantsixfan springs to come in starting at 1400 and be all in by 2800. IIRC the mech advance slots were .380" long.

Initial timing is 16*, any less and the idle quality is pretty crappy.

Vac advance pod is a VC239 can, set about midway through the adjustment.

Unfortunately my specialty tool source (Lou) left his timing light in vegas so I haven't been able to get any better info about my timing setup just yet. Have one on order though.

And I like my tall tires! Cruising around 2500 RPM at 70 mph and I can pull strong uphill past anything slow without dropping down into second who needs an OD?

Red79, a few little things to try:

First get two books: Super Tuning and Modifying Holley Carburetors, by Dave Emanuel; and Holley Carburetor Handbook 4150 & 4160 Selection, Tuning & Repair, by Mike Urich.

If possible install an o2 sensor in concert with an Air/Fuel ration meter. I have been struggling to dial in my 8007 for a number of years, and until I hooked up the [url=http://www.bob2000.com/carb.htm]02 sensor[/url] I was driving blind. I had tried every conceivable combination of power valves, jets, springs, pump shot and cam and still couldn’t get it right… I feel your pain. LOL

Once A/F ratio could be monitored while driving I was able to come close to a good tune. I have a big lumpy cam, that pulls 3-6â€￾ Hg at 700 rpm in D, and 11â€￾ hg at 1150 rpm in park, Clifford headers & intake, 2600 rpm stall converter, 3.55 Suregrip, 24 ½â€￾ tall tires that makes for 3000 rpm at 60 mph. All this now yields 18 ½ mpg, and a slant that runs a ¼ mile about 16 seconds flat calculated, and the eighth mile in 10.3 sec @ 68 mph.

The 512 jet, 25 squitter, 6.5 power valve, and secondary metering block is #134-34 (I think about equal to a 52 jet) is stock settings from factory. I found that 512 jet (51jet) was a bit lean, and now have 53 jet installed, but plan on a 52 when I next order from Summit. When I use a PV below 6.5 I would get a flat spot. 95% of my driving takes place under 500 feet in elevation. Elevation is one of the variables effecting jet selection.

What is your cruise vacuum reading?

One question: does your Clifford intake have heat, or provisions for heat from heater core coolant loop?

Remove the carb from manifold, drain its fuel, tip it upside down, and set throttle plates so the long transfer slots are just covered by them in both primary and secondary bores, but make sure throttle plates are not tight to the bore walls. Gently screw in both idle mixture screws until they just seat, and back out 1 ½ turns. Keep 512 jets & 4.5 power valve in place for now. Hold off installing new secondary metering block as well, we only want to tune the primary side first. Use Vaseline to lubricate all O rings you encounter to make reassembly easy, and not damage O rings each time carb is opened up.
Tip: I use a large coffee can as a carb stand, it works great, and holds fuel dumped from bowls as well.

Install black secondary diaphragm spring which will cause the secondary throttles to stay closed all the time, and check that secondary diaphragm is not ripped. (a dab of Vaseline where screws pass will prevent future rips)… I hope you also purchased the quick change spring cover kit with the spring kit. Reinstall the carb, hook up vacuum gage to center front vacuum tap at carb’s base, sure PCV and other vacuum hoses are attached, start engine making letting her warm up and come off choke. Adjust float levels in both primary and secondary fuel bowls so fuel just dribbles down side of carb while engine is idling.
Tip: I use a $1 clear plastic bottle from Walmart like one of those red catsup squeeze things to prim the primary fuel bowl via the air vent before trying to start engine. With some fuel in front bowl the engine will start right up, with no prolonged cranking.

Adjust both idle mixture screws equally for highest vacuum & highest idle speed. Don’t adjust the idle speed screw or the relationship of transfer slot and throttle plates will be lost. If engine is idling too fast, or not fast enough adjust timing until it is correct. Adjust accelerator pump so it squirts as soon as throttle is moved.

Go for a ride, record how, and at what speed & rpm the carb reacts such as bog, flat spot, surging at steady idle etc. If it runs fine at slow speed, and there is no off idle bog or flat spot you have successfully tuned idle circuit.

If bog, or flat spot happens at higher speed when main jets are running, you may be lean and need to go up three jet sizes to 54. If there is a flat spot at still higher rpm when booting it try a 6.5 power valve.

The books will explain all this, and much more. Now you are close to a good tune, and basically have a two barrel with the black spring installed. Run this way for a tank or two checking fuel millage while waiting for books, quick change spring cover, and a reusable Mr. Gasket #4255G to arrive.

More on secondary tuning later once the primary is dialed in.

Ted will help as well, he sets up his cars for millage and torque. I found Holley tech line to be less help than Summit tech line. Holley has several tuning youtubes on their web site that were very helpful.

Bill

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks for all the tips, you've provided me with just what I was looking for, a good baseline to begin the tuning process. I'll try and answer as many questions you asked as I can:

First, I'll try and fix the wideband sensor+driver I have. It's very old, and was working for a while, but right now it only reads properly for about 30sec at a time before spiking at 25.0 and staying there. I think the sensor is dying and needs to be swapped out.

I live at around 2000ft elevation, and that's where I daily drive, but I do take a lot of trips ending up below 500ft. Maybe I'll need to end up tuning a little rich at altitude.

I don't have a good cruise vacuum number, the gauge is all over the map depending on where I have the throttle. What's a good representative road speed that I should use for cruise?

The clifford intake is unheated, and that's definitely contributing to my poor drivability right now. The car ran much better cold when it was 60 degrees out in the morning--but recently it's 36 degrees in the morning, and the roughness is playing a big role in motivating me to get all this tuned better. I saw a picture of the water heating provision you built for your clifford intake in another thread, I feel like I would benefit greatly from a similar setup during the winter.

I'll keep the carb the way you recommended, butterflies just covering the transfer slots (no slot visible below the plate), 512 primaries, 4.5 PV. I'll plug the sec diaphragm port until the springs get here, that should keep them closed, right? I'll also swap to a #25 squirter and put the cam back on the 1 setting to try and calm down the massive shot it's pushing now and start tuning with something closer to the stock carb setup.

It also seems like it's a good time to fix my speedo haha.

Thanks for all the help! I'll update with my progress and any new info.

I don’t recall, and can’t find the change in elevation that requires a jet change. I think if you tune to 2000’ you will be fine to sea level, and a little rich at 4000’. Remember air is less dense at higher elevations then at sea level, so a smaller jet would be needed as you go up the hill.

I don't have a good cruise vacuum number, the gauge is all over the map depending on where I have the throttle. What's a good representative road speed that I should use for cruise?

Find a good stretch of flat road, drive it at a various steady speeds with as little throttle movement possable to lessen vacuum gage movement; record the number & rpm. A little mathematical manipulation and you can get MPH.
36 degrees and high humidity equals carburetor icing, crappy fuel millage, poor drivability, and fuel dropping out of suspension causing puddleing in manifold. This causes accelerated engine wear, and a lean condition. You need to address this deficiency, or the car won’t run right until next summer.
That will work if you block off passage between diaphragm housing and carburetor body.
Yup, that would help calculating fuel millage, and collecting data.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Is hooking up some kind of custom water circuit (like yours) the only real option for me? I suppose I could rig up a heat pipe from one of the primary tubes.

Also, a few different sources including clifford's website say that there's a water jacket on their 4bbl slant manifolds, but for the life of me I can't see where I'd connect to it. Is the description wrong?

Yes, they do on their later manifolds. If they would show a picture of the bottom that would make it easy to see.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Ahh, understood. I must have an older model. I guess I'll look into fabbing up a water block like wjajr.

On that note, since my intake is mounted on the head, does anyone have measurements I can use to make a setup like this?

I have never seen a new water heated Clifford manifold in the flesh, just a photo of one on their web site after I had modified my unit.

There were four bolt holes on the bottom side of my old stile manifold, using their dimensions & layout as a starting point. Using two half inch chunks of aluminum plate one made into a square doughnut, the other a cover with two brass fitting found at hardware store. Then I made some gaskets to build a water tight sandwich with a hollowed out center.

It ain’t pretty, rattle can paint job is deceptive, but it works. Several years ago when we moved 90 miles closer to the Mall I had to move both old cars to the new digs during January. It was 15 degrees that day, the engine started right up, ran flawlessly all the way, and made plenty of heat to stay warm in a drafty ragtop.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks, it'll probably be a little while before I attempt it, but that'll get me started!

I'm contemplating switching my fixed blade fan for a clutch or electric unit as well. I've noticed that the front of the intake manifold stays quite cold, and the front fuel bowl as well long after the rear of the manifold is warm. So maybe the fixed fan is hindering the even warmup of my manifold in this cold weather.

Progress! Slapped the carb back together, bolted it back on and let it warm up. Didn't do any idle tuning yet, but drove it up and down the block, and the car seems noticeably peppier. When stalled up, it even had enough oomph to overcome the rear drums and give me a peg leg burnout haha--could never break them free before. Plenty of tuning still to go, but it's nice to see such a difference right off the bat.

Ahhh, the old redneck dynamometer used again… I have one of those at the end of my street as well.

Progress; good.

How does the exhaust smell after this adjustment?

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Still smells rich at idle, so I'll see what some tuning does. Also, got a deal on a shiny new wideband from a friend, so the guesswork will be over in a few days.

Nice, get that thing hooked up, and report back. In the meantime adjust or fine tune those idle mixture screws. Keep in mind that the emulsified fuel mixture ratio (fuel and air bubbles) dribbling out of idle hole into air stream under throttle is fixed, and by turning idle mixture screws in or out is actually controlling volume of said fuel mixture delivered. Idle circuit will be controlled by volume of air added to emulsified fuel stream to make an ideal mixture.

So we shall wait for new metering to be installed before any changes are offered up. Are you using an A/F gage, or digital volt meter to read air/fuel mixture from driver’s seat?

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I went all out and got a lightly used Innovate kit with a sensor, driver, and wideband gauge--should serve me well for tuning, and I can move it to the other cars when necesasry.