Brand new to Thermoquads- a few questions I need help with

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hudskit

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Good Evening, All,

I have recieved a nice rebuildable core Carb- series 9103 - a 77 400 HP application that I'd like to use on a set of 302 heads I'll be installing soon on a 273 .

I have been doing my research and I have noticed my target carb- a 1973 340 AT unit has the same Primary jet- 4098/ .098- but has a smaller secondary jet -5143/.143 existing compared to the desired 340 jet- 5137/.137 - and smaller metering rods -existing 2211- compared to the desired 340 AT metering rod 1966- so is this , if I can find the parts , a good idea ? and if so , a reasonably do-able one? What else will I need to be on the lookout for as I try to make this swap to this late model carb? I've already ordered a set of the brass floats and a shop manual , along with a rebuild kit.

does anyone know what the second set of numbers below the model number mean ? Mine has 103 S below the 1903 S on the base plate..

Thanks and Happy Holidays to All!
 
You can decrease the size of the rods, they are only soft brass alloy. IIRC Edelbrock rods can be adapted. a smaller diameter rod is richer than a fatter rod as it is less of a restriction in the jet ID. You can also enlarge the jets. There were over 10,000 Carter carb OEM applications, each one was unique in metering. Your 273 is gonna need a lot less fuel than a 340 so youll probably have to fatten up the rod or reduce the jet. an A/F meter will greatly help.
 
If I'm not mistaken, the 9103 is a lean burn TQ. It does not have the nipple on the base for the ported vacuum for the distributor vacuum advance. You can add a nipple if you are careful and get it in the right place.
 
A TQ with 1 3/8 primaries will respond better on a smaller engine then 1 1/2.
I've been using a 6138 (72 340) TQ on my 318 with a whiplash cam for a few weeks, I originally had it on an Air gap intake with square bore to spread bore adapter after getting it adjusting the Air door and setting it to the longer stroke setting on the Accel pump it was running good. I have now went backwards and am running the same TQ on the 318 with a stock cast iron 340 intake manifold. Lost alot of low end power.
The main thing with running the TQ on a smaller engine is air flow, mine seemed to run better and had good low end power on the air gap manifold.

If your set on running a TQ on your 273 I would try getting one that was on a 318 and stay away from lean burn models and other emission component models.
 
At some point the lean burn TQ's came without an idle speed screw. So, you might want to make sure you have an idle speed screw, first.
You might want to look for a Carter "Strip Kit". They came with an assortment of rods and jets. Yeah, I agree, the smaller TQ(smaller primaries) might be the way to go.
 
In the case of carbs, bigger IS not always better. As posted, the smaller primary TQ would probably serve your application much better with the proper build of internal parts & pieces.
 
The Carb Shop has some TQ parts.
Find a different TQ, a small primary unit with idle screw and vacuum port for a distributor.
Edelbrock rods need to be bent shorter @ 3/4 of an inch. The rods themselves are much thicker and require some work to fit. Ether turned down in lathe or design a new tree to fit them on. BTDT

Rods and nets have always been a PIA for these carbs. I have over the years bought junk carbs just for there rod and jets to make my own kit.
 
Strip kits for TQ’s are out there but are pricey and desirable TQ’s are getting pricey as well.
 
Agree with comments above.

TQ is a great carb. But I would look for an earlier 6XXX series carb, with small pri bores [ 1 3/8" ]. This is a much better starting point. Get a gasket/overhaul kit & it will bolt on & run with minimal tuning reqd.
 
I'm to the point in life where I really don't wanna piss with old carburetors anymore. The new little Street Demon carburetors from Holley are a modern TQ born all over again. I have one on my Ford truck and it's one of the best running carburetors I've ever owned. They are so close to a TQ, they may as well have named it that.
 
I bent and clipped the rods and made my own tree top to hang the rods in. Not pretty, but it worked. Sorry, no pictures of this old trick of mine.
 
Good Evening, All,

I have recieved a nice rebuildable core Carb- series 9103 - a 77 400 HP application that I'd like to use on a set of 302 heads I'll be installing soon on a 273 .

I have been doing my research and I have noticed my target carb- a 1973 340 AT unit has the same Primary jet- 4098/ .098- but has a smaller secondary jet -5143/.143 existing compared to the desired 340 jet- 5137/.137 - and smaller metering rods -existing 2211- compared to the desired 340 AT metering rod 1966- so is this , if I can find the parts , a good idea ? and if so , a reasonably do-able one? What else will I need to be on the lookout for as I try to make this swap to this late model carb? I've already ordered a set of the brass floats and a shop manual , along with a rebuild kit.

does anyone know what the second set of numbers below the model number mean ? Mine has 103 S below the 1903 S on the base plate..

Thanks and Happy Holidays to All!
OK the 103 is the 103rd day of the year it was built. Means nothing for parts.

I love the ignorance about thermoquads. I have 2 of them for my 340.
You can find the correct parts if you look hard enough on ebay and online.

Here is a pdf for the manual to rebuild and tune
https://www.carburetor-parts.com › ...PDF carter-tq-manual.pdf - Mike's Carburetor Parts
You also need to reglue the transfer wells for the primaries with JB Weld Marine, there are tutorials on how to do this
I would not try to manually modify any parts since they will never be precise look for original parts.
Here is the online Bible for id's A Carter Thermo-Quad Guide

I would start small on jetting, primaries are available. .090 and 0.127 for secondaries. Leave the rods. And only change 1 thing at a time for tuning. Go up 2 steps on primaries always 1for secondaries
Adjust rods for drivablity.
The dash pot is essential for the secondaries. It needs to pull the door tight with vacuum, the door should be 1 1/2 turns after making contact with boss in back.
Look for the secondary tool using 2 screw drivers sucks.
Use only x rings for primary seals.
The tree should be 1 /2 turns from the bottom.
They need a lot of choke to start.
Mixture screws should be 21/32 to 24/32 from base to top of screw as baseline.
Honestly i would look for something starting with a 6xxx since these are pre lean burn and are a little easier to tune. You can use parts of the one you have.
 
Good Evening, All,

I have recieved a nice rebuildable core Carb- series 9103 - a 77 400 HP application that I'd like to use on a set of 302 heads I'll be installing soon on a 273 .

I have been doing my research and I have noticed my target carb- a 1973 340 AT unit has the same Primary jet- 4098/ .098- but has a smaller secondary jet -5143/.143 existing compared to the desired 340 jet- 5137/.137 - and smaller metering rods -existing 2211- compared to the desired 340 AT metering rod 1966- so is this , if I can find the parts , a good idea ? and if so , a reasonably do-able one? What else will I need to be on the lookout for as I try to make this swap to this late model carb? I've already ordered a set of the brass floats and a shop manual , along with a rebuild kit.

does anyone know what the second set of numbers below the model number mean ? Mine has 103 S below the 1903 S on the base plate..

Thanks and Happy Holidays to All!

Try it as is before making any changes. If running that carb make sure you have a working choke. Set your distributor to run without vacuum advance. You will need to adjust the secondary air valve. I second getting the right tool. It is easier to drill jets than to make or modify rods, plus it is reversible. The best TQ's to run are early car and later trucks with ported vacuum for the distributor. I have run a box stock 71-73 340 TQ on a 273 and it was perfect.
 
I saw some instructions a while back where you could drill and add a ported vacuum for advance
Here is the youtube

In my humble opinion, I would find one with a vacuum for vacuum advance before attempting this. There are plenty of good ones with advance already set up.
 
OK the 103 is the 103rd day of the year it was built. Means nothing for parts.

I love the ignorance about thermoquads. I have 2 of them for my 340.
You can find the correct parts if you look hard enough on ebay and online.

Here is a pdf for the manual to rebuild and tune
https://www.carburetor-parts.com › ...PDF carter-tq-manual.pdf - Mike's Carburetor Parts
You also need to reglue the transfer wells for the primaries with JB Weld Marine, there are tutorials on how to do this
I would not try to manually modify any parts since they will never be precise look for original parts.
Here is the online Bible for id's A Carter Thermo-Quad Guide

I would start small on jetting, primaries are available. .090 and 0.127 for secondaries. Leave the rods. And only change 1 thing at a time for tuning. Go up 2 steps on primaries always 1for secondaries
Adjust rods for drivablity.
The dash pot is essential for the secondaries. It needs to pull the door tight with vacuum, the door should be 1 1/2 turns after making contact with boss in back.
Look for the secondary tool using 2 screw drivers sucks.
Use only x rings for primary seals.
The tree should be 1 /2 turns from the bottom.
They need a lot of choke to start.
Mixture screws should be 21/32 to 24/32 from base to top of screw as baseline.
Honestly i would look for something starting with a 6xxx since these are pre lean burn and are a little easier to tune. You can use parts of the one you have.
 
Thank you much for the input - this is a truly useful post. I have indeed found a 6139 carb to use instead of my 9103 so I'm listening to the chorus of "I've bought the wrong carb to work with"- which is how I usually start off on these things.....:). Do you have a preference for rebuild kits that will have the x shaped gasket?
 
Over the years,, I've probably bought a hundred TQ kits from all kinds of brands, and only one didn't have the "X" type constant feed o-rings(if that is what you are referring to).
 
You do NOT need the X type o rings. Just use fuel resistant std o rings, 3/8" OD, 1/16" wall thickness. This is all that I have used since the 70s, never had one leak.
The X type are a very flimsy design.
 
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