Finally Fed up- Opinions on a New Carb Please!!

[bandt]

Hey Guys,

I know we've been down the carb road a thousand times but before I spend almost 500 on a carb can I get some opinions please.
I have a tired, leaky, out of tune 650 double pumper, no choke. I can 't stand it any more.

The biggest question is I have heard that the 340 benefits from a bigger carb say 750 dp or the old school tune of of putting a 800CFM TQ on. I have also read that bigger carbs are better for top end not so much bottem end. I am more interested in bottem than top.

What I was thinking is getting the new Proform Aluminum street series  http://www.jegs.com/i/Proform/778/67257/10002/-1?parentProductId=1273573

What I need to know is do I get the 650 or 750 DP.
Its a 72 -340 20 over with 70 replacement pistons (higher compression), Air Gap intake, headers, 284/484 cam, auto slap stick-manual valve body, 4:10 rear end.
Would like to stick to mech. secondaries but would like to hear opinions. Any help would be greatly appreciated, gotta pull the trigger in a couple days my inlaws are going to bring it back for me on there way back from Florida.

Thanks Brian

[MEK-Dangerfield]

You will love the Proform.   

I hesitate to recommend the 750 since you are more concerned with bottom end... But you don't have a stock set up either.   

[bandt]

Heard lots of good things about Proform.

I tend to agree I'm leaning towards the 650.

[Cooter]

Whatcha gonna do with that old Holley 650 DP? If you concerned with leaking, then I reccomend against the TQ....

[bandt]

TQ notorious for leaking? I didn't realize that.

Where is everybody? Noticed the site has been kinda dead lately. Not getting many responses and I'm outta time. 


Brian

[Cooter]

TQ's are like the GM counterpart, the Qjet carb's..If you get a good one, then you better hang onto it...That PLASTIC center section gives ALOT of problems..Between warping, cracking, and generally just simply leaking at the little "wells" in the bottom, other than this they are great carbs..BTW, a TQ is a vaccum secondary carb..Yes, I know the butterflies are mechanical, but that big 'ol air flap on top isn't controlled by linkage, it's controlled by the engine's load..

Alot of people don't like a Holley and usually it stems from not knowing anything about how to "trick" a holley...By this I mean, how to make them stop leaking, perform on the street with good manners, etc...People nowadays like instant grtification and want this damn thing to run Perfectly right out the box for 50 plus years.Sorry, this isn't the case with anything...Even Fuel injection..

Personally, I'd go with either carb as they will both work, but the lower CFM rating will be better out the hole than the larger 750..You gotta remember, your only dealing with a 340 cubic inch engine...750 CFM is ALOT of air to be moving with such a small engine with little to no mods. (IE: Racing cam, high compression, race ported heads, etc)..

[brads70]

I would say with the 4.10 rear gears and to choose between 650 or 750 cfm.....I'd go 750? Look at what they had stock from the factory?

[bandt]

I've read through a lot of info and I'm fairly intimidated about tuning this carb. I've read some horror stories and they sound just like what I will be dealing with.

Longer duration cam, way out of range for idle mixture. Throttle plates are into the transfer slot, guys are drilling holes in the butterflies. The other issue is the power valve will probley be out of spec for manifold vacuum causing it to leak at idle loading the carb making it even harder to tune. AHHHHHH

This carb has adjustable air bleeds, so hopefully no hole drilling.

[MEK-Dangerfield]

No, the carb will come with the standard 6.5 power valve. No chance of it leaking at idle and loading up the carb. With the carb I bought, I only adjusted the idle and the float settings. The jets were spot on by looking at the spark plugs. I know this can get frustrating, but we can help you along. Are you going with an electric choke? That was another thing I had to back off.

[bandt]

That's great info MEK-Dangerfield

What cam are you running in your car? Do you have the 650 or 750? I already had a 650 DP on the car it was horrible. Don't have the carb yet so as soon as its running I will get a vacuum reading and see where I am. What sort of vacuum reading are you getting with your set up?

Yes it does have the electric choke.

Thanks for the offer to help out, I think I'll need it. Nothing has ever been straight forward with this car.

Brian

[MEK-Dangerfield]

That's great info MEK-Dangerfield

What cam are you running in your car? Do you have the 650 or 750? I already had a 650 DP on the car it was horrible. Don't have the carb yet so as soon as its running I will get a vacuum reading and see where I am. What sort of vacuum reading are you getting with your set up?

Yes it does have the electric choke.

Thanks for the offer to help out, I think I'll need it. Nothing has ever been straight forward with this car.

Brian

I really don't know the specs on my cam, but it's a Lunati and it's fairly lopey. I run an 850 carb simply because that is as big as I could go and still have a choke(440 engine). I have an electic choke. That beats the heck out of the manual one I used to have...The cable was always sticking.     My vacuum reading is like my gas mileage on the hiway...Barely into double digits.   

[bandt]

I've read a lot of talk about mechanical vs vacuum secondaries. It sounds to me like you need a fairly stout motor, light weight car, and low rear gear to run one with a A/T. I may have been better off going with vacuum secondaries as I don't have the full list of requirements.


My 340 isn't that stout- factory heads 1.88 intake valves, air gap, headers, 70 replacement pistons, 284 dur/ 484 lift Mopar cam.  Not sure what this combo is good for hp wise.
Its a stock A/T 72 Challenger, I'm guessing 33-3400 lbs, not light.
It does have a low rear gear - 4:10.

I'm getting the Proform 650, should have it next week. So second guessing my choice at this point won't do any good.

What do you guys think?

[MEK-Dangerfield]

Actually I'm glad you decided to play it safe and go with the 650. As for going with the vacuum secondaries...You will get better gas mileage for sure.     I probably should have gone with vacuum secondaries too, but oh man does my car like mechanical secondaries.   

[bandt]

Actually I'm glad you decided to play it safe and go with the 650. As for going with the vacuum secondaries...You will get better gas mileage for sure.     I probably should have gone with vacuum secondaries too, but oh man does my car like mechanical secondaries.   

I'm not to concerned about gas mileage, I really just want to get the car to run right. Like I said it had a Holley 650 on it already. It was a dog off idle, that may be a combination of things. I know the cam isn't optimal but I hope the carb isn't a contributing factor. This is my first carbureted car and I have no experience to draw from as far as getting it set up.
I bought the car with the engine work done. As far as I know maybe the previous owner never got it set up right with this combination of parts.
It will really suck to go the through the aggravation, time and expense to end up with the same result he did.

Brian