Rebuild or Replace 850 TQ for a Mild 340?

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Mattwood440

Mattwood440

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A previous owner put a 9009S Thermoquad on my 72 Duster 340. It has sat for years and has not run since I bought. I discovered yesterday that it has the "850" cfm TQ carb, date coded 1975. My question is this; should I rebuild/reuse this carb or get a reman smaller one, like how it came originally? It is a #s matching car that I'm restoring to mostly stock appearing. I'm going to reuse the RV2 ac compressor and it is an automatic w/ power brakes. The engine is going to have 10:1, machined J heads w/ 2.02 valves, a mild cam, and long tube headers. I'm only looking for 300+ hp and the car is going to be used for cruising in traffic. Thanks in advance.
 
Personally, I’d give a rebuild a try. Kits are cheap.
I would not use a smaller TQ or another carb under 750cfm.
I’d also look for an earlier year TQ.
 
Rebuild the one you have or



If you're wanting smooth running and any help with gas mileage, get a TQ

that has ported vacuum for the distributor
IIRC, lean burn and others do not have ported vacuum.
To install one is not the big of a deal

Be sure to make sure the throttle shaft bushings are tight, TQ's
Are known to wear the out prematurely
 
Last edited:
Brooks James said:
Rebuild the one you have or



If you're wanting smooth running and any help with gas mileage, get a TQ

that has ported vacuum for the distributor
IIRC, lean burn and others do not have ported vacuum.
To install one is not the big of a deal

Be sure to make sure the throttle shaft bushings are tight, TQ's
Are known to wear the out prematurely
Click to expand...
I didn't know that. Good info.

@rumblefish360 I'll order the rebuild kit. Any brand better than others?
 
Beware of generic TQ rebuilders.
They crossbred parts often.
There are at least 9 different Phenolics
that I recall and only the matched one from
the factory will give optimal performance
 
Use the TQ you have with a new kit.

I have found veeeeery little difference in performance/actual operation of the 800 & 850 TQs. Secondaries are the same, only difference is 1/8" between the primary bores.
 
rumblefish360 said:
Prematurely? Prematurely!!!!

If a 48 year old carb! LMAO!
Click to expand...
Ok, I'll bite
Rephrased: in the 45 yrs plus that I have been working on Mopar TQ's, l have only seen a few throttle plates that had zero play (not including new)

I'm not going to engage in any more verbal scraps with you, it's impossible to tell a "know it all" anything
 
Last edited:
Brooks James said:
Ok, I'll bite
Rephrased: in the 45 yrs plus that I have been working on Mopar TQ's, l have only seen a few throttle plates that had zero play (not including new)
Click to expand...
Oh my Lord, relax!!!! In the 40 years I’ve been playing with MoPars, or anything even outside of cars, items that are man made and move around wear out. How can they not? Below, is a quote by you;

Be sure to make sure the throttle shaft bushings are tight, TQ's
Are known to wear the out prematurely
Click to expand...
So I jokingly (or at least tried!) to have a laugh at the carb being old and wearing out. Being the carb is a moving part, it wears out. You said “prematurely” which I thought was funny. But let’s dive into that one a second here.

Just what is premature wear on a 40+ year old moving part?

And you got upset with this? Duuuuuuuuuuude, really?
Well, OK then.

I'm not going to engage in any more verbal scraps with you, it's impossible to tell a "know it all" anything
Click to expand...
LMAO! OK then. Why don’t you PM me for an adult conversation and point out to me where I’m wrong and you were right.
I certainly don’t know everything! I have a host of threads asking for help here. But perhaps your extensive knowledge base can straighten me out? I’m all up for learning something.

At the same time, expect the same back. Looking forward to working with you.
 
I have only bought a few new carbs in my life. Almost all rebuilt carbs ran very well without tight throttle shaft bushings. If set up right and adjustments made the throttle shafts would have to be very loose to make a difference. All my cars run 50 year old original Carter HP carbs.
 
On our race cars, a loose throttle shaft does not seem to make
any performance difference unless it is so loose it binds up. Probably
gives you a few more CFM (Joke?).

Now on a streetcar where it has to run in different throttle/vacuum positions, it
could possible cause a tuning/drivability problem.
 
:thankyou:

Thank you, my friends! I ordered a kit with all the bells and whistles from Mike's Carburetor Parts. This should be fun! For years I was a dealership tech well AFTER carbs were phased out so I've never rebuilt one. Unless you count the motorcycle carb I tried to rebuild 20 years ago, which never did run, so we won't speak about that...
 
I agree with buying a kit and rebuilding the carb. Lots of good stuff on YouTube. I do have one question, though. In your original post you said that you had a Mild 340 and an 850 CFM Carb. Different people have different ideas of what a mild 340 is. I was just wondering if 850 CFM is a bit much for a mild 340. I have what I would call a moderately modified 340. It is at 375 HP. A 750 CFM Edelbrock works great on it. It is JUST a question. I don't know enough that much about matching carb CFM to engine size and HP level.
 
That is the beauty of an air valve type carb [ Edel, Carter, QJ, ] or a Holley vac sec. The engine determines the air it wants, not the right foot. So even if the carb is slightly oversized in CFM, it will work correctly.
 
Mattwood440 said:
:thankyou:

Thank you, my friends! I ordered a kit with all the bells and whistles from Mike's Carburetor Parts. This should be fun! For years I was a dealership tech well AFTER carbs were phased out so I've never rebuilt one. Unless you count the motorcycle carb I tried to rebuild 20 years ago, which never did run, so we won't speak about that...
Click to expand...
Take pics during disassembly of the carb for reference
 
Brooks James said:
Take pics during disassembly of the carb for reference
Click to expand...
Always a good move for anything.

The Car Tech (?) book “Carter Carburetors” has a step by step process for all 4 of the Carter carbs. New additions of the books included the Edelbrock carbs. The pictures and instructions are very good.

The OP will find the carb very simple but putting it back together again can be a trial if it’s done out of order.
 
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