340 carburetor selection advice

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Dartndude73

Dartndude73

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lithia fl
I know there is a ton of information out there. I’ve gone over many many posts, checked out all kinds of info online, talked it over with other car guys and checked with carb manufacturers and so on. So here’s the deal. I’ll try to be as detailed as possible.
I have a 73 dart sport. I’ve had the car now for almost 3 years but I am just now in a position to do some serious work on the car. I bought it from a wanna be flipper who was in over his head. The car sat for 8 years before I got it. So the usual. Bad gas, rusted tank, screwed up fuel lines etc,etc.
Up until now what work I have done on it is just to get it started so I can move it on its own power. Tons of electrical issues. I literally have removed a bucket full of screwed up wiring under the hood. I can fire it up but it won’t start after I shut it off or it stalls until it cools down. So trying to set timing and adjust the carb have been a chore. “For an example the distributor was wired reverse polarity”. It started but the timing mark was under the water pump so far I couldn’t even see it. Bad grounds, alternator wired wrong. Got that straitened out. I still have a lot of electrical work to do.

So to the point. I need a carburetor. The 600 edelbrock that’s on it doesn’t make sense to me and is trashed. The old weiand intake is going too.
Specs; engine rebuilt by original owner to stock - 1973 340 block 9 to 1 compression, stock heads, so 1.88 intake valves, stock rockers, Headers, 2 1/2 exhaust I will be replacing the stock type mufflers with some flow masters I have. MSD 6al with MSD coil and Mopar performance distributor. I replaced the pickup and lightened up the mechanical advance with different springs. I have installed a fuel cell in trunk. I have 3/8 lines, carter electric fuel pump, 5/16 return line, pressure regulator and gauge to install. I have a couple old cool cans around I may add one just because I live in FL. It has a rebuilt by original owner 727, B&M shift kit and a B&M 3500 stall converter, I did find a B&M torque converter box in the trunk. I checked the rear it has 411 sure grip. Spin the wheel 1 revolution the driveshaft turns 4 times an a little. According to the original owner it has a Lunati bracket master cam - 480/480 - 292/ 292. I picked up a brand new edelbrock performer dual plane rpm intake, super deal couldn’t pass it up. I have a phenolic spacer for under the carb and will be blocking off the crossover when I install it. The car will be mostly street with occasional trips to the track. Need to be able to beat my wife's 98 trans am running 13.1 quarters.lol - so it’s not a race car.
so let’s start with cfm’s, I’m thinking this combo “other than the heads” is a good match for a 750 vacuume secondaries. I have had “other than Chrysler” cars with similar specs that a 650 worked great. My big block cars were 750’s. I’m thinking a 650 even with removing the choke and adding a stub stack getting me a few more cfm’s will possibly be sacrificing a lot of top end HP. The 750 will cost me on the bottom end but how much? So what do you all think? I don’t have a ton of money, parts are expensive and have a lot of work to do. Want to get the carb correct the first time using what I already have to work with. Your responses will be greatly appreciated!
 
This is a no brainer. 800 cfm Thermoquad, 6000 series, which is what came on the car originally. Plenty available on Ebay that just need a clean up & overhaul kit. You could also contact Woodruff Carburetors, one of the sponsors on this forum. A mate recently bought a pair of Competition Series TQs [ rare ] from them & they were reasonably priced & arrived as described.
 
The 73 340 was nowhere near 9:1 compression "stock", so if it's truly 9:1 It AIN'T stock. So let's get that out of the way. I agree with either of the above choices. The Thermoquad or the 3310 750. Be ready to tune either and the Thermoquad has a steeper learning curve, but IMO, is superior.
 
Bewy said:
This is a no brainer. 800 cfm Thermoquad, 6000 series, which is what came on the car originally. Plenty available on Ebay that just need a clean up & overhaul kit. You could also contact Woodruff Carburetors, one of the sponsors on this forum. A mate recently bought a pair of Competition Series TQs [ rare ] from them & they were reasonably priced & arrived as described.
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Really depends on the intake manifold he chooses. Some (like my Air Gap) are only drilled for the square bore carbs.
 
Get a 4 corner idle circuit holley or quick fuel 750 mechanical secondaries . You can use the air bleeds to lean up the mixture without taking the car off. They are right under the the air cleaner in the body. Bigger is leaner and you can control High speed or idle . Primaries and secondaries. You can also square the primaries and idle off of the secondaries so you are not into the emulsion jets at idle which gives a dead spot.

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I read that you have the RPM intake employed.
I’d run with the above post by Oldmanmopar. The carb he recommends is a very good one and isn’t a hair raising experience to tune. Just start with the basics and move on from there IF even needed.

Going through your combo, I myself just don’t like the cam very much. Other than that, the 750 won’t give away low speed torque. Everything should improve. A larger carb is not an automatic penalty for power loss.
 
Bewy said:
This is a no brainer. 800 cfm Thermoquad, 6000 series, which is what came on the car originally. Plenty available on Ebay that just need a clean up & overhaul kit. You could also contact Woodruff Carburetors, one of the sponsors on this forum. A mate recently bought a pair of Competition Series TQs [ rare ] from them & they were reasonably priced & arrived as described.
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Thank you
Bewy said:
This is a no brainer. 800 cfm Thermoquad, 6000 series, which is what came on the car originally. Plenty available on Ebay that just need a clean up & overhaul kit. You could also contact Woodruff Carburetors, one of the sponsors on this forum. A mate recently bought a pair of Competition Series TQs [ rare ] from them & they were reasonably priced & arrived as described.
Click to expand...
 
Thank you all for the replies!! Right now I’m leaning towards the 750 Holley 3310. I have more experience with holley’s and I can pick one up pretty reasonable. The thermoquad I did some research on I have checked out prices and everything Bewy said is on point. Olmanmopar and rumblefish advice on the Holley/ quick fuel looks good too. I took a quick look online at pricing I will check look into them all in detail. Also the cam choice seemed a little off to me too. At this point my priority is to get the electrical strait. Put the intake and carb on it and fire it up see how it runs. If I eventually do some upgrades I want to be in the ball park with the carb.
As a side note, the guy I bought it off of really didn’t know much about the car. I was lucky and I called a phone number written on the back of the title and it was the original owners son. That is where I got most of the info on the car. So again thank you for taking the time to respond to my post.
 
The thermaquads worked good when they were all that was available. Once you put a bigger cam in its hard to get the rich lean adjusted perfect do to vacuum loss and RPM changes where torque range is.

Not saying it can't be done I've seen guys make them work . You'll be playing with it a long time. And how old are those carburetors now? In a pure stock class they must be used. Other then that they are not worth the aggravation unless you are looking for original.

This is just my opinion . Think about it and ask around. We run all types of motors here I love the a 4 corner carb on anything with a larger cam. Other wise when you drop it in gear you'll have what we call a mule trying to walk with a load. Rather then horses at a gallop. I wouldn't even consider a TQ on any performance motor with today's fuel. Listen to one of these carbs in gear on the street from a dead idle with pump gas.





 
Bewy said:
This is a no brainer. 800 cfm Thermoquad, 6000 series, which is what came on the car originally. Plenty available on Ebay that just need a clean up & overhaul kit. You could also contact Woodruff Carburetors, one of the sponsors on this forum. A mate recently bought a pair of Competition Series TQs [ rare ] from them & they were reasonably priced & arrived as described.
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Yup. Here is the perfect place for a factory 73 intake and TQ. A member here is selling some Competition TQ’s right here for a pretty tasty price.

I’d get a carb from him and find a 71-74ish intake manifold. Sometimes you can find them for free. And that’s a really good price.
 
If you are going with a Holley or Holley clone, the first thing you have to check is the emulsion stack. They usually come with 3 or 4 holes open. That’s way too much.

You’ll need to restrict the transfer slots because they are all too big.

Unless you are running the linkage 1:1, you don’t want it idling off the secondaries. And if you do do 1:1 linkage you need a power valve in the secondaries because you are going to cruise on the primary and secondary main jets.
 
I run a 2.5 to a 4.5 primary power valve depending on Vacuum at idle with a larger Cam. Vacuum at idle divided by two. No power valve in the secondaries. You can play with air bleeds. All 4 corner carburetors come with a secondary idle adjustment screw to use it for idle after you square the transfer ports on the primaries.

There were times with the secondaries closed it was idling high with the primaries square. Then you can drop the idle RPM with the primary idle adjusting screw. If its idling to low you would raise it with the secondary idle screw. You should never go past square on the primary transfer ports.

The carburetors I buy usually have a blank power valve in the secondary metering block. Probably why its there and why they sell them. I would never buy a new a standard double pumper for any car with a large cam any more. If so you usually have to drill holes in the venturi valves. That is the old school way and I see many double pumpers that it is done to.

4 corner is the new way for carburetion. The latest a Holley sniper fuel injection system .
 
The 3310 will be pig rich on the idle circuit IMO with really no way to lean it out. I would get something more modern with more adjustability.
 
Dartndude73 said:
Thank you all for the replies!! Right now I’m leaning towards the 750 Holley 3310. I have more experience with holley’s and I can pick one up pretty reasonable. The thermoquad I did some research on I have checked out prices and everything Bewy said is on point. Olmanmopar and rumblefish advice on the Holley/ quick fuel looks good too. I took a quick look online at pricing I will check look into them all in detail. Also the cam choice seemed a little off to me too. At this point my priority is to get the electrical strait. Put the intake and carb on it and fire it up see how it runs. If I eventually do some upgrades I want to be in the ball park with the carb.
As a side note, the guy I bought it off of really didn’t know much about the car. I was lucky and I called a phone number written on the back of the title and it was the original owners son. That is where I got most of the info on the car. So again thank you for taking the time to respond to my post.
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I think you're making a good choice with the 3310. The 3310 was the first Holley I ever used after tinkering with Carters for decades.
If you're familiar with Holley's like you say, stay with them, they are much more tunable than Carter's or should I say much more forgiving in transition with varying vacuum signals at low RPM.
 
A TQ will work just fine with longer duration cams. They tune the same way as other carbs. With bigger cams, as with other carbs, the IFR may need enlarging. So simple, remove the air horn, voila, there are the IFRs ready to be drilled. Jets & met rods easily changed. More bypass air maybe reqd & many TQs already have some bypass air holes in the base, which can be enlarged. With really long duration cams, I do not enlarge the BA holes because it could induce nozzle drip with the sensitive triple booster design, which gives the TQ it's great throttle response. Instead, I drill small holes in the sec blades until I get the T-slot position correct. The engine doesn't care where it gets the extra idle air from, as long as it gets it....
Do not see any benefit of 4 corner idle system, just harder to balance for no gain.
There are tuning recommendations for the TQ in the MP bulletins for both SP & DP intakes.
The TQ is ideal for what the OP wants.
Some actual numbers. I tune a 455 Le Mans that has a Mopar 850 TQ on it. Street car, 3900 lbs without driver, 3.31 axle, T400. Factory intake & hi-po exh manifolds, 236 @ 050 cam. First time drag racing for the driver & no testing done for jetting or timing, ran 11.78 @ 115.

With a bigger cam 254 @ 050, Victor, headers, it ran 11.65 @ 119 with no tuning & inexperienced driver. Idles @ 800 rpm in gear with 48* idle timing.
When leaving the dragstrip, the owner offers Holley owners gas in case they are running low...

LeMans
 
I'll ask the same question as always.... what's the idle and total timing (all in).

Cam is 230 @ .050, not big at all. Shouldn't have a problem getting a good tune on it, which it may be lacking now.

Low compression, larger cam = plenty of initial timing

An old 3310 with the old emulsions would be fine on that. My 340 with a smaller cam 214/224 and LD340 ran great with a 3310. It's all in the tune up.
 
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My 340 is similar to yours except 10:1 and cam is [email protected] I run 93 pump gas.
get a qft750 dp with 4 corner idle. In FL you don't need a choke.
I'm in FL and run one with this setup:
PJ 72 SJ 84 MAB .029
Emulsion stack 4 hole metering block .028/plug/.028/plug If using 3 hole block .028/plug/.028
PVCR .055 6.5PV
IFR .032 moved to bottom position (very important to improve cruise AFR)
IAB .067 all 4 idle screws approx 3/4 turn
both throttle plates even 1/2 turn out from fully closed.
Ignition 28* initial 34* total mechanical vacuum advance at cruise mid 40*s
With no choke the motor will run like $hit (lean) at idle until it comes up to operating temp. If motor runs without having to feather for a minute or two cold engine, the idle is to rich.
This setup works for me at sea level and FLs humid air. In the dog days of summer you can drop the jets to 71/83.
 
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Holley 750DP

I ran it on a 11.3Scr alloy-headed 367/A833/3.55 with a 292/292/108cam
Yes with holes drilled in the primary throttle valves. One in each, 6or7/64ths IIRC. 14* initial. 700/750idle. My 292 measured 248@050. After three intakes, and three carbs, I settled on the 750DP/AirGap. I always like to say; once you've run a DP, you'll never go back. I once gave some church friends a ride, the 4 of us had to be 1000 pounds. That cam with that weight, had a heckuva 1-2 punch! They giggled like school-girls.

My 3650#DD-me in it, didn't like the meager 9.44 starter gear; but 3.55s is all I wanted to run, since I live in the country about 25/30 minutes from work.
Between the too-small starter gear, the high cruise-rpm, and the atrocious fuel-economy, I had to make a decision; after just a few months, I pulled it.

In it's place, I put a 223/230/110 cam and she promptly ripped off a 106 Quarter at 12.9 on 245/60-14 street tires. My favorite combo in that car. I'd still be running it, if the lobes hadda stayed on the cam.
 
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Great replies to my post. And again thank all of you for taking the time to help me out! It’s obvious to me that the 750 is the way to go. I’m really looking hard into all your suggestions. I got a lot more solid info than I had expected. The tuning #’s you all shared will be real helpful. While I’m getting my electrical issues straitened out and installing the rest of the fuel system. I’ll be looking for a deal on a carb.
 
Ok, I found a great deal on a barely used quick fuel 750 with mechanical secondaries. It looks brand new. Not a scratch on it $375.00.
 
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