So, I've had the dart running for about two weeks now, its nothing special, 8.9 ish compression, Oregon cam 819 (.436 lift 264 duration) recurved distributer, hurricane intake w/ holley 350, and dutras.

However, I have got a flat spot right about 2500rpm. It seems to be giving way to much fuel, as the only way to get past it is to ease way out of the throttle. It will then slowly build up out of it.

Also, it isn't possible to stand on it from a stop. This results in falling flat on its face till you back off the throttle. I assume it stems from the same flat spot...

If I could get this worked out, this engine feels like it will get up pretty good!

Oh, and it don't like to (read, won't hardly) rev past 3500. Same problem? Or could that be I have too fast of an advance curve? (yellow and blue springs)

The holley is pretty stock out of the box, idle mixture set is about all we have done. 61 jets, 30cc pump shot, 31 shooter(?) orange pump cam set in #1 hole.

It's not getting any more mileage than 18 either, but that may just be the nut behind the wheel

A couple of must haves for on the fly tuning is a vacuum gauge hooked up to the port under the float bowl while driving and an O2 sensor and gauge in the cockpit, so you can relate the vacc reading to whether it is going lean or flooding out...

Long ram manifolds are a little finicky on the street unless the manifold is warmed up enough to keep the fuel from dropping out of the airstream.
Another thing to look at is the pump cam, the longer long ram manifold the hyperpak likes a longer stronger pump shot to over come the lag in signal at low rpm when tromping on the go pedal, all of my Holley 4 barrels have had to go to the pink cam in #1 to work right...also look at the cam profile not the quantity pumped, the orange cam tends to run out after 70% of the throttle plate opening while the pink cam still has lift and pumps right up to being WOT. Make sure to qualify the pump spring to pump lever under the bowl, the factory sets this a little loose and can delay the pump shot as the spring and lever takes up slack before it pumps.

At 2500 you should be in the mains, so if it's flooding then your jetting is too high... that being said make sure that your vacuum advance is hooked up to the port on the side of the metering block not below if your rear end ratio is 2.76's with an automatic you need to slow down your advance curve as well.

There's a real juggling match when fiddling with timing and the carb, it will be a give and take in adjustments between them.

Good Luck.

Makin it work = fun part! Do what Dan sez.
Question though is this a 2 or 4 barrel?
You said 350 and may be its a 390?
The AFR meter and vacuum gauge are your friends.
Carb work is like fishing, sometimes the same bait Doesnt work.
Of course spark equipment must be top notch(known good)
Those jet #s and shooters are in the ballpark (2 or 4 barrel)
I will assume float level and fuel pressure are correct.
Take ALL the slack from the squirt spring/lever arm.
Unhook vacuum advance and remove this variable for the time being.
Regardless of Initial timing make sure total timing is around 32 or so
and dont mess with it until you get the carb dialed in.
If a 4 barrel pop the c clip off the secondary and disable it.
Test drive> if good put heaviest spring(black?) in pod.
>bad test Look for throttle blade open too far(transfer slot)
If a 2 barrel > go to transfer slot ( what I am saying here is that if you have had to crank the idle screw in more than a 2 from blade being closed
you will have to address why and fix it) Also 2 bbl that was intended for
Class racing will be fat and smelly on the idle and transition circuit because generally they are used on a bigger engine>more work.
Regarding carb work it is important to describe any issue you have in
terms of throttle blade angle instead of RPM as obviously a manual trans car say in overdrive like mine is doing like 75 mph and still on the idle circuit @ cruise (18-20 inches vacuum and 1/16 pedal) or on the other end of the spectrum a car with a low (higher numerically) gear ratio and auto trans /loose converter maybe 10 inches of vacuum @ 65 and need 1/4 throttle to achieve same speed.
Doing small accelerations in the area of the issue is how you narrow it down and making adjustments that are relevant in that area ONLY .(one @ a time)
I just described what I would do in the first 10 minutes. If you get the idea it may take some fiddling and research you are on the right track.
My wild assed guess would be that Dan is right and a big manifold needs lots of fuel , Heat is good , real good, It only costs a very few HP on top if @ all and adds so much drivability Every where else. Flat is lean so add fuel. Gurgly or sounding like it is gargling is rich. Again my guess i that
you are Lean through through transition area (your 2500 rpm) and
Fat and gurgly on top. Lean will dry rev but will not rev under a load.
Wait until you get the carb 95% before you add vacuum advance or
mess with the timing it will cross you up and add alot of valuable time to the learning curve. Then apply the same 1/8>full throttle approach to your timing under a load AND @ cruise. There are excellent posts on spark timing in this Forum. Godbless

_________________
" Inventor of 24 grit wart remover"
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What has been said is on the right path. Large volume intakes require richer mixture, and or manifold heat for daily driving. Cool ambient temperatures in humid weather will cause an unheated intake to ice, and or pull fuel out of suspension onto inner surfaces of intake causing a lean condition, crappy fuel mileage, and very poor drivability.

Because a slant is a small displacement engine, and yours has a rather large carburetor attached to a voluminous cold intake manifold I’m trending in the lean condition direction as cause of drivability problem.

Flat spot most times is a sudden lean condition developed when throttle plates open too wide during low air velocity through carburetor to be able to pull enough fuel through the main jets and enrichment circuit to maintain correct air fuel mixture. As suggested above larger jets and bigger longer accelerator pump shot is needed to bridge the time needed for engine (think air pump) to increase rpm to where enough air is moving for the carburetor to do its job.

Keep in mind you are tuning four circuits: idle; transition, main, and enrichment.

I started to list out all the tuning steps, and decided it is all too much without illustrations detailed lists of various Holley tuning parts to get on to written page here. I know I will leave out something, or mislead by way of syntax or sloppy writing, so I will just recommend two books that cover Holley Tuning. Keep in mind your two barrel is just the primary front or half of 4150 (mechanical secondary) or 4160 (vacuum secondary)…

Holley Carburetor 4150 & 4160 selection, tuning, & repair; by Mike Urich. A little red book.

Super Tuning and Modifying Holley Carburetors Performance, Street, and Off-Road Applications; by Dave Emanuel.

These two publications got me through tuning my Holley 390 on a low idle vacuum engine, with the installation of an o2 sensor, and Holley TV; it’s their You Tube video help department. Watch them all.

_________________
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 everyone,

For a while I had thought it was a rich, as it had been told to me by many people 'if ya got to back out of the throttle to get it goin', it is too rich' and with true duals, I could tell the rear 3 were running pig rich (just a factor of
unheated manifold, as it turns out)

But wjajr was right, it does seem to be a lean condition instead. Holley TV diagnoses a popping thru the carb as a lean condition, and while it doesn't do this often, I've noticed it will do this every once in a while, say, when its is stood on from a roll (It will bog down, pop occasionally, and then pick back up and get going) and if it hasn't warmed all the way, starting from a stop will make it want to pop and stall.

BTW, yes this is the 2300 series, deemed a 'stock replacement' for Ford products by Holley. The 'circle track' type carb was tempting at first, but I made sure that wasn't what I bought.

I do need to get the AFR and vacuum gauges, but the price has been kindof scaring me off...
Which leads to an additional question - wideband and narrowband whats the difference? pros and cons off each?

Ya'll are a great help!

Oh, and on the manifold heat, Aussiespeed offers a water plenum heater, but I've heard that water heat takes so long to warm up that you might as well not have it. How many have made exhaust heat on a manifold that doesn't have it, and how?

I am currently using a 2300 500 cfm although I have a blo thru turbo setup.
I cannot comment on Aussie manifold heating.
Wide band only. Narrow band is 80's technology.
Innovate LC-1 is awesome and fairly cheap. EBAY
I stick with my wild assed guess see post above.
Books that were recommended are excellent and there is a chapter
on road race tuning that you should bookmark.
You will probably have to buy some small drill bits and pin vice.
Or you can buy metering plate with changeable jets. As mentioned above it uses the same Primary metering plate as 4150. ebay ,buy blank jets for PVCR and Emulsion channel , IFR (idle)
You will need the reusable bowl gasket , I like the blue one also the nylon
float bowl washers. Yes you have to remove the float bowl that many times.
Sound like work? Like i said its the fun part! But look on the bright side
after you master this carb and manipulate all of it passages to get it to do what you want youll have a skill few way beyond changing a jet.
Could you maybe get by with a couple of simple fixes? Maybe.
Fix the flat spot first. Then remove extra fuel in the above mentioned
4 circuits (although the fifth is the fuel pressure and level).Godbless

_________________
" Inventor of 24 grit wart remover"
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I wrote a lot of posts on tuning the hyperpak for street use and all of this is pertinent....The reason you are getting a lean out in a long ram is some of the fuel is vaporized at the operating temp....anything liquid at high vacuum climbs the runner walls (higher rpm and throttle plates partially closed)...when you step on it and the vacuum drops...all of that drops to the runner and plenum floor and only a little is left to make it to the cylinder creating a lean out. Sadly unless someone has done this kind of work they are shooting in the dark on carb tuning...after a few months of tuning I found the happy place for a 390 cfm 4 barrel and a 600 cfm 4 barrel for racing....and neither needed to be pin vise drilled, it is all in the jetting, secondary plate indexing, and pump cam with shooter choice. Oddly I did all of this with a vacc gauge and a narrow band lambda sensor (narrow band will get you close, but then you have to make the fine tuning on your own with some plug reading...which should be done instead of basing your adjustment 10% on the sensor readings...it an naturally aspirated carb build, it's not EFI so it can be close but doesn't have to be perfect...and in a long ram a wide band might show lean while driving, then you enter the ram tuning rpm range on the highway and wash down your cylinder walls with the excess gas that is puddling in the plenum, so remember these are tools to help but you are the ultimate decision maker in where to go).

The hyperpak liked to have the ambient temperature in the 50's...but if tuned right you could get it to fire up in the winter time....but it would quickly fail out when the choke pulled off even after the engine itself was warmed up....water heat won't affect the manifold until the engine begins to make excess heat to warm up the coolant in the jacket...that can take up to 8-10 minutes in very cold winter conditions...per my previous posts I had gone with dutra duals, and welded up a heat box that fit under the plenum to provide direct heat as soon as the engine was running...

This actually provided two advantages....

1) I used a runner to both exhaust pipes for the box, so that the alternating exhaust pulses between the two pipes would keep the box supplied and evacuated between the exhaust cycles like an "H" or "X" pipe.

2) Allowed the plenum to remain heated and kept fuel from puddling in the plenum and causing "slugging" with excess fuel when the vacuum dropped on moderate acceleration....All being said and done, I think if I had more time to explore the possibilities heated air cleaner snorkel might also have benefited as well (similar to the stock air cleaner and heat stove)....

I will also note you are on the right track I found that the rear 3 runners sit in a hot spot near the firewall and brake master cylinder that doesn't get much flow since it's removed from the fan, and any air flowing by the block goes low and ducks down near the z-bar or linkage. This phenomenon caused me to unsquare my carbs to be a little leaner for the primary and secondary near the fire wall (cylinder 4-5-6), and richer on the other side (cylinder 1-2-3) where it was cooler. This became more paramount when I split the plenum so the slant became similar to a V engine and so individual tuning of the 1-2-3 bank and 4-5-6 bank was needed for optimum performance.

Get the books, look at some of my posts on the "hpak", and go from there... Although my time is spotty at the moment, I'll look in from time to time to see if I can help...note that the hurricane manifold is slightly shorter than the hyperpak, so carb jetting and tuning will be a compromise between the shorty clifford and the hpak...also the "ram-tuning" will occur at a higher base rpm so to get benefit of any ram tuning you might only get that 7th cylinder at 4000 rpm.


-D.idiot