Thermoquad jetting help?

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abqphilbert

abqphilbert

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Albuquerque, NM
I'm hoping somebody out there can make a recommendation on what size primary jets, metering rods, and secondary jets I should try (start with). I have a 9022 S Thermoquad that I want to rebuild for my 318 four-speed Dart. This carb was originally on a 1974 360 truck engine with automatic transmission. I haven't been able to find anyone local that knows much about these carbs, so I'm looking for somebody that knows more about these carbs than I've been able to learn from my own research so far.

I live at 5,500 ft. elevation, and have found the other carbs I've used had to be jetted a little leaner here than they would at or nearer to sea level. I'm guessing this carb is jetted too rich for my engine even if I was at sea level - but I don't really know that to be correct. I haven't rebuilt it yet or tried to run it as it's currently jetted. I figured I'd do a bit more research first, and hopefully same some time and work later.

This car is a daily driver. My engine is a 1973 stock displacement 318, original heads with 1.88 intake valves, standard-sized exhaust valves, ported & polished, 9.8 compression, solid-lifter COMP cam with .468 lift on both intake & exhaust, Doug's headers, Edelbrock Performer intake, and electronic ignition. The car has an A-833 overdrive and an 8.75 axle with 3.23 and sure-grip.

I understand that whatever jets I start with may turn out to be less-than-perfect, and may require more adjustment later, but I'd really like some input from anyone out there willing to offer it, so I can start with something that has worked well for somebody else.

Hope to hear from some other members.
Thanks .
 
Oh hell, a upgraded 318?!?!
run the carb as is. I think you'll be a bit rich, but not to far off.
 
I agree with rumble, your primary should be around 98 with around 128 or so secondary. These carbs were jetted back in the day for 100% fuel ... not 10% ethanol so you might be close or a bit rich. Plop it on with fresh plugs and see where it's at, there are a lot of other tuning that can be done before changing jet size like sec air door, removing the choke will lean it a bit. If your still rich you should be able to find jets for it.
 
I don't disagree with what's been said, BUT, I would try it like I is first. At least that way you'll have a base line, plus Thermoquads are a little different than other carbs. It might be that it's about right. Never know till you try.
 
Thanks for the info folks. The primary jets in it now are 4095 (0.095s), which I'm thinking may be ok. I know there are a lot of different metering rods. This one currently has 75-1966 rods in it, which may also be ok. I'm willing to try it. The secondary jets in this carb are 5143s. Not knowing any better, I would have looked for something like some 5125 to 5135 secondaries. Sounding like I should bolt it on as it is and see how it goes. Good idea on starting with fresh plugs.
 
abqphilbert said:
Thanks for the info folks. The primary jets in it now are 4095 (0.095s), which I'm thinking may be ok. I know there are a lot of different metering rods. This one currently has 75-1966 rods in it, which may also be ok. I'm willing to try it. The secondary jets in this carb are 5143s. Not knowing any better, I would have looked for something like some 5125 to 5135 secondaries. Sounding like I should bolt it on as it is and see how it goes. Good idea on starting with fresh plugs.
Click to expand...

Just tossing this out there, I ran one from a 440 on my teen, and it ran great. Only problem I had was getting rid of the off idle stumble, but when I went WOT or just cruising, it worked great.
 
The 1966 rods are very good rods for performance. Make sure the choke pull off is good so you don't get the dreaded off line bog. If you need to jet up I can drill out the jets on a precision lathe.
 
Does your TQ have the can hanging on the front? thats an altitude compensator. No idea what it does but thats what its called. lowering the tree is akin to a global leaning. Raise it for global richening (global is an EFI term that means shifting the A/F across the board, on a carb thats with a mechanical change).
 
pishta said:
Does your TQ have the can hanging on the front? thats an altitude compensator. No idea what it does but thats what its called. lowering the tree is akin to a global leaning. Raise it for global richening (global is an EFI term that means shifting the A/F across the board, on a carb thats with a mechanical change).
Click to expand...

That compensator is exactly for that reason it opens to create a controled vacuum leak leaning out the mixture.
 
pishta said:
Does your TQ have the can hanging on the front? thats an altitude compensator. No idea what it does but thats what its called. lowering the tree is akin to a global leaning. Raise it for global richening (global is an EFI term that means shifting the A/F across the board, on a carb thats with a mechanical change).
Click to expand...

I wouldn't call it global. It simply leans the primary side.
 
Global for the primary side, yep, that'll do.
 
Thanks again to all. It will be at least a few weeks before I get this TQ built and on the car, but will update the post with results then.
 
when jetting a Carter AFB, AVS, TQ. they all call out jet size, and metering rod by diameter. you need to remember changing a jet from .060 to .061 is less change then a .090 to .091. and you can NOT guess what your change is if you change both the jet AND rod. its best to change the jets first then work on the rod. BUT remember a little is a LOT. as little as .003" can be felt. the eledlbrock copys of AFBs, AVSs, have rods that have bigger step change that stock chrysler rods. so if your eldelbrock is is not running right try rods more like the chrysler rods in size. i do have a program to calculate the actual change in surface area. even changing both jet and rod at the same time. if i find it i will post it. found it. *http://clarkehackworth.com/files/JetsAndRods.html ........i just tried it seamed to not do the calculation. ill get my son on it hope the URL doesnt change. i found out the rod size needs to have number higher than .000. so if you want to calculate the jet change only just put a rod size the same in the cruse step and the power as the same number. in both the #1 jet and #2 jet. that will calculate the jet only change. i hope i said this right.
 
Thanks Moe. I appreciate it. I understand what you're saying. I just bought a box of spare TQ parts (for $12) that included some smaller secondary jets, as well as two different sizes of metering rods, so I have a lot to work with. I'll see what I come up with using the formula, but regardless, I have several different sizes to work with now on primary and secondary.
The Edelbrock I'm using performs ok, but it tends to percolate after shutting off a hot engine. After reading about the TQ, with the benefits of lower fuel temperature and the secondary air flap, I just decided I want to go this route, rather than continue to try to fine-tune the Edelbrock. Especially living in the mountains, I think the TQ will be a good workable solution. I'll see.
Thanks again.
 
Make sure you install a "THICK" carb to intake gasket. The stock gasket is an excellent part.

You can bend the AFB rods 3/4 of an inch shorter, clip the ends off to use in place of the stock rods. They will be two step instead of three. If you "NEED" to get bigger primary jets, make sure that they are precision drilled.
 
i think the computer pro gram may have a major error. so iam trying to get in touch with my son to work out the trouble.
 
Thanks Rumble. Good point. I just got the carb kit I had ordered and it came with good base gaskets, plus a nice 1/4" spacer. I don't have a spacer under the Edelbrock I'm using now, but I'm thinking I'll use this one in the kit when I put the TQ on.
 
That 1/4 inch spacer is the gasket for the carb to intake.
 
even thou my carb program is not working right now. still follow the guide line of change ONLY the jet OR rod at one time. and size change of .001" on the rod is less than on the jet.
 
my carb jet / rod program had an error in it. my son has fixed it now. i checked it out. and it is fine. if you want to check jet to jet only, enter .000 for the rods. and with rods and jet change, it will calculate changing jets and rods at the same time. you cant guess a change of both at the same time. http://clarkehackworth.com/files/JetsAndRods.html
 
Thanks Moe. I just checked it out and see how it works. Thank your son for me as well. It'll probably be the weekend before I have time to go through the process, but I can use the program to calculate the various percentage of increase and decrease with the different combinations of jets and rods I can come up with. It should save a lot of time if I need to re-jet once I get the carb ready to run. Unless I get lucky enough to hit the right combination the first try. Hey, stranger things have happened. Ha Ha.
 
iam glad you like it. i came up with it cause one can not guess what the change is when changing both the jet and rod. i have other AFB hints. ill try to find them and post when i can.
 
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