Thermo-Quad metering rod measures

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Mecki

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I have a Thermoquad that I have never used because it's missing the metering rods. Probably that's the reason why it ended up to me. It's in pretty good condition and not too worn. The number stamped on the base plate is 9097S (1976 lean burn 400cid A/T) but that's not necessarily true for the rest of the carburetor since I have no knowledge of the history and it has been apart, blasted and rebuilt before. The cover has casting # 6-2146 which according to some information should be the last non smogger version and used on 73-74 400/440 and some 75-77 trucks. Apparently some export car versions could have had this cover after 74, maybe also this 9097S from 1976 if it comes from an export model.

Anyway the metering rods are missing and seems to be impossible to find. QuadrajetParts.com had 75-1966 rods up for sale but that store is no longer working since the owner has passed and that was the only place I found.

I was thinking that this can't be rocket science and to fix some other rods to fit must be possible. The problem is that I don't have a rod to take some measures from. The measures what I need is:

Material thickness.
Distance from the tip to step 1.
Distance from the tip to step 2.
Distance from the tip to step 3.
Distance from the tip to the top of the rod measured to the inside top of the eye.

The measures of the thickness of the different steps are found in the tables and is the start point to find some rods that could be fitted to a Thermo-Quad.

Maybe some one already has this info or a rod to measure. Or maybe even some spare rods to sell?

Any help would be appreciated. I don't want to scrap this carburetor just for missing rods.
Thanks
Mecki

Edit:
Does anyone know if all the Carter rods with # 75-xxxx are interchangeable. Some YF and YFA 3-step rods are available.
 
Last edited:
IIRC the 67 FSM has metering rod ODs for Carter carbs, maybe your year FSM does as well
 
DionR said:
@Vaanth
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Thanks DionR. That Vaanths guide is really good and has most of the information you can hope for.

But it doesn't have manufacturing drawings of individual parts. Since I don,t have a metering rod to start with I don't know the length of the rod and the positions of the steps. To try to find something that could be fitted I first need to know what I'm looking for. That's hard without a sample rod or length measures.
 
Mecki said:
Thanks DionR. That Vaanths guide is really good and has most of the information you can hope for.

But it doesn't have manufacturing drawings of individual parts. Since I don,t have a metering rod to start with I don't know the length of the rod and the positions of the steps. To try to find something that could be fitted I first need to know what I'm looking for. That's hard without a sample rod or length measures.
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If Vaanth doesn't have any info, I can measure up a rod for you. I have loose ones, shouldn't be hard to get the info in a bit.
 
1729280036313.png

I found these on ebay:

CARTER YFA / YF 0.075"x0.057"x0.047" Metering Rod​

Could be possible to fit in a TQ if the lenght is enough.
 
I have some TQ rods, but what you want to know is what combination to use with the jets you have. Do you know what jets are in your carb?
 
Just get a new Street Demon and be done with it. It's a modern Thermoquad.
 
Here's a 75-1966 rod. I would have to go digging to see if I have any other loose one, or take one apart.

Did my best with my HF calipers, I suspect there are better ways and more accurate tools. I didn't match the economy step either.

Not sure how the midrange step works since there are only 2 parallel sections. Maybe the long taper midpoint is the midrange step?

75-1966.png
 
I would have to measure some others to see if the steps are at consistent distances and only the diameters change. So not enough info to be able to replicate them.
 
DionR said:
Here's a 75-1966 rod. I would have to go digging to see if I have any other loose one, or take one apart.

Did my best with my HF calipers, I suspect there are better ways and more accurate tools. I didn't match the economy step either.

Not sure how the midrange step works since there are only 2 parallel sections. Maybe the long taper midpoint is the midrange step?

View attachment 1716317165
Click to expand...
It would make sense .655 is idle. The taper is transition and the .0455 is the richest. I see no reason why a two step rod like in the Edelbrocks or Street Demons couldn't work if they are the right length. I have some of each if yall want a comparison.
 
RustyRatRod said:
It would make sense .655 is idle. The taper is transition and the .0455 is the richest. I see no reason why a two step rod like in the Edelbrocks or Street Demons couldn't work if they are the right length. I have some of each if yall want a comparison.
Click to expand...

I grabbed a rod out of an AFB strip kit to measure when I dug out the TQ rod. Took longer to do the TQ rod than I expected so I didn't do much with the AFB rod except an overall length and base diameter. The ABF rod seems to match the material used, but is about 3.125" long overall. And the steps are pretty different.

I could see someone with a lathe being able to to shorten and step an AFB rod to match the TQ rod, but I wouldn't expect taking the AFB rod and cutting it off and bending a new leg in it being very successful.

20241018_151500.jpg
 
And this is what I think of when I imagine someone using the AFB rod in a TQ without modifying it.

main-qimg-391a3114283d231d3b8011453476e3ca-lq


:rofl:
 
DionR said:
I grabbed a rod out of an AFB strip kit to measure when I dug out the TQ rod. Took longer to do the TQ rod than I expected so I didn't do much with the AFB rod except an overall length and base diameter. The ABF rod seems to match the material used, but is about 3.125" long overall. And the steps are pretty different.

I could see someone with a lathe being able to to shorten and step an AFB rod to match the TQ rod, but I wouldn't expect taking the AFB rod and cutting it off and bending a new leg in it being very successful.

View attachment 1716317202
Click to expand...
Boy, that would have to be some intricate lathe.
 
RustyRatRod said:
Boy, that would have to be some intricate lathe.
Click to expand...

No argument.

I'm no machinist, but I would bet it would have to be a small lathe and the rod would need to be supported at both ends until it was cut to length and the cuts small and gently.

But I'm just guessing. And I didn't stay at a Holiday Inn Express last night either.

I would guess they did it with a lathe or something similar originally. They had to have a way to build them some how.
 
66fs said:
I have some TQ rods, but what you want to know is what combination to use with the jets you have. Do you know what jets are in your carb?
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The jets I have are the (stock?) 120-4098 = .098" .I'm planning to put this TQ on a 440 and I found in the -73 FSM (first year TQ on a 440) that all 440 had 75-1966 rods. So that's what I'm trying to achieve. Finding a pair of 75-1966 or something close would of course be the best solution. Primary jets should be available if needed.
 
Mecki said:
The jets I have are the (stock?) 120-4098 = .098" .I'm planning to put this TQ on a 440 and I found in the -73 FSM (first year TQ on a 440) that all 440 had 75-1966 rods. So that's what I'm trying to achieve. Finding a pair of 75-1966 or something close would of course be the best solution. Primary jets should be available if needed.
Click to expand...

That 1966 rod is what I measured and posted dimensions of above. :D

PM if you are interested in them.
 
DionR said:
Here's a 75-1966 rod. I would have to go digging to see if I have any other loose one, or take one apart.

Did my best with my HF calipers, I suspect there are better ways and more accurate tools. I didn't match the economy step either.

Not sure how the midrange step works since there are only 2 parallel sections. Maybe the long taper midpoint is the midrange step?

View attachment 1716317165
Click to expand...
Good drawing. Thanks for your effort. If the rod was 10x bigger I would already be on my turning machine. This could probably be done whit a small grinder fixed instead of a cutting bit and turning the supported rod with low rpm. The bending would be the last step hoping it doesn't break.
 
Remember the relationship of rod to jet will dictate AFR. If you use a bigger jet then you need a bigger rod to maintain the same AFR as the restriction has to be the same to meter the same amount of fuel.

Try this guy:

THE CARBURETOR SHOP

At one time he would make rods and kits for sale, not sure if he still does.
 
Hysteric said:
Remember the relationship of rod to jet will dictate AFR. If you use a bigger jet then you need a bigger rod to maintain the same AFR as the restriction has to be the same to meter the same amount of fuel.

Try this guy:

THE CARBURETOR SHOP

At one time he would make rods and kits for sale, not sure if he still does.
Click to expand...
Thanks for the info. As the rods are nearly impossible to find I just have to go with what I can find and then match the jets to the rods.

I have visited that site. Interesting place and could be that they have what I need. They don't have anything listed online and the communication appears to be complicated. It took some time to find out that they even have email and an address where to send. It would probably be an interesting experience to visit the shop.
 
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