Thermoquad mods that work.

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Bewy

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A few comments first on the earlier thread on the forum by Brook James:
- there is no need for additional atmospheric vents on a TQ. It has 3 already. A 1050 Dominator gets by with two 5/16" vent tubes.
- enlarging n/seats. Going too large [ or just larger ] does 2 things: it raises the fuel level & also makes it more difficult to maintain a steady fuel level. The TQ has HUGE f/bowl capacity, which is probably why Carter used the small 093 n/seats....to maintain good fuel control. 101 n/seats would cover just about any situation that uses pump fuel [ as against E85/Methanol ]. If using the larger 101 n/seats, the float level setting needs to be changed from stock. If using Nit floats & stock setting is 29/32", then change to 1" [ 3/32" lower ]; this is with 6 psi fuel pressure.

- I think there is little to be gained by removing the choke housing. Very few engines will use the 800+ cfm that the TQ can flow, despite the wishful thinking of some. Removing the choke blade, linkages & the shaft across the air valve blade is worth doing because they interfere with the air flow.
- holes in the t/blades. These have nothing to do with idle air bleeds. They are there to add bypass air [ BA ] so that the t/blades are in the correct position for that engine & it's component parts. At some point in the TQ series, Carter used the front two body screws as a means of providing BA. The holes in the bowl & gasket are slightly enlarged to allow for this airflow. Be careful swapping bowls/gaskets etc. If these holes are not already enlarged, it is easy to do it. These carbs are easily recognised; there are two holes inside the choke tower, in line with the screws. The actual metering of the air is done by the sizing of the holes in the carb base. The reason Carter did this is because the sensitivity of the booster design could induce nozzle drip from air being drawn past the boosters. Hence bypassing the boosters to supply the reqd air.
- if more BA is needed, say for a big cam, it is better to drill the sec blades, NOT the primaries for reasons above.
 
The mod shown in the pic below I have done countless times over the years & in EVERY case it provided a veeeerry noticeable increase in performance.
The bullet ends of the discharge tubes [ DT ] are cut off just where the bullet shape ends. I got this idea from the comp Series TQs. I use a Dremel with a 1" cut off wheel to do this.
Next, you need to solder closed ALL the small holes in the DT. Use emery to clean the surface. Then use an electric sol iron [ about 80 watt ] & resin cored solder. Do NOT use a gas flame, it will oxidise the brass & the solder will not bond. After soldering, run a drill up the DS to clean out any solder that may have got in.
I always remove the choke linkage; doing this exposes a small T shaped hole in the air valve [ AV ]. I braze a small piece of steel over this hole because in the original configuration that hole was blocked by the choke linkage. I have not tried this without blocking that hole. If you do not have access to brazing/welding gear, you can pop rivet a small plate over the hole.

- Set AV spring to 1.5 turns.
- Start with 137-143 sec jets. Drill out smaller jets.
- Sec high speed air bleed. You can see it in the pic, the long brass tube that sits inside the fuel jet. I have only found 3 sizes that Carter used, but we have limited numbers of TQs in this country, so there may be others. I have found 027, 029 & 039-040 air bleed sizes. You want 039-040. If smaller, drill them out. You drill the pinched section of the tube where it protrudes into the air horn. Use a 039-040 drill. It is better to do this in two stages, as removing 010 in one step may break the drill bit. Use a 033-035 drill first & then finish with the 039 bit.
Adjust the WOT position of the AV for a dimension of 0.800-0.850" from the dimple to the black body. This can be varied if needed or experimenting.
One final tip. With the AV dashpot held in with vacuum, you want about 0.100" of free play between AV & the AV stop on the airhorn.

The front portion of the AV has a bend in it; the AV on the Comp Series does not have this, it is straight. have not tries bending it straight to see the effect.

DSCN0253[1].JPG
 
Just so you know, there are more things to consider than just cfm or increasing cfm when modifying any carburetor. Increasing flow efficiency.
Reducing turbulence.
Increasing signal strength.
Reducing pressure drop over the top of carb.
Just to name a few.
 
Quite agree. That is what the above mods addressed: reducing flow restriction & turbulence. A by product might be an increase of a few cfm, but more cfm was not the primary aim.

The butt-meter will feel an immediate improvement with the above mod.
 
Bewy said:
Quite agree. That is what the above mods addressed: reducing flow restriction & turbulence. A by product might be an increase of a few cfm, but more cfm was not the primary aim.

The butt-meter will feel an immediate improvement with the above mod.
Click to expand...
I believe removing the choke horn and smoothing the entry in that area will help contribute to improving the things I mentioned in my first post.

I’m not saying the mods you did do not work and are duly noted to things I will try.
 
Bewy said:
The mod shown in the pic below I have done countless times over the years & in EVERY case it provided a veeeerry noticeable increase in performance.
The bullet ends of the discharge tubes [ DT ] are cut off just where the bullet shape ends. I got this idea from the comp Series TQs. I use a Dremel with a 1" cut off wheel to do this.
Next, you need to solder closed ALL the small holes in the DT. Use emery to clean the surface. Then use an electric sol iron [ about 80 watt ] & resin cored solder. Do NOT use a gas flame, it will oxidise the brass & the solder will not bond. After soldering, run a drill up the DS to clean out any solder that may have got in.
I always remove the choke linkage; doing this exposes a small T shaped hole in the air valve [ AV ]. I braze a small piece of steel over this hole because in the original configuration that hole was blocked by the choke linkage. I have not tried this without blocking that hole. If you do not have access to brazing/welding gear, you can pop rivet a small plate over the hole.

- Set AV spring to 1.5 turns.
- Start with 137-143 sec jets. Drill out smaller jets.
- Sec high speed air bleed. You can see it in the pic, the long brass tube that sits inside the fuel jet. I have only found 3 sizes that Carter used, but we have limited numbers of TQs in this country, so there may be others. I have found 027, 029 & 039-040 air bleed sizes. You want 039-040. If smaller, drill them out. You drill the pinched section of the tube where it protrudes into the air horn. Use a 039-040 drill. It is better to do this in two stages, as removing 010 in one step may break the drill bit. Use a 033-035 drill first & then finish with the 039 bit.
Adjust the WOT position of the AV for a dimension of 0.800-0.850" from the dimple to the black body. This can be varied if needed or experimenting.
One final tip. With the AV dashpot held in with vacuum, you want about 0.100" of free play between AV & the AV stop on the airhorn.

The front portion of the AV has a bend in it; the AV on the Comp Series does not have this, it is straight. have not tries bending it straight to see the effect.

View attachment 1716149195
Click to expand...
Wow, just what I've been looking for !!!
Specific info in detail.
Thanks Bewy
 
@Bewy Good show!

The race TQ’s have the straightened secondary door. I have not run mine yet. At the rates 1,000 cfm, a mill to take advantage of it doesn’t yet exist in my stable.
 
Rumble.
Yeah the differences in the air door [AD ] of the Comp Series & production carbs was what I was referring to. The shape of both carbs in that area look similar, so why the change, I do not know.
Only thing I can think of: as the AD starts to open, more air gets past the AD on the CS series on the initial opening; secondaries activate sooner?

I have a couple of CS 850 carbs. After doing the above mods to a production carb, butt-meter could not tell the difference between the two models.
 
@Bewy I have a few TQ’s I have cut up and ground on in an effort to seek information on not published as well as to find limitations on grinding away at various parts of the air horn. Experimentation came to a stop at a point. Other more pressing things in life take precedence of course. I’m looking forward to my garage being built for many automotive reasons. The process is painfully slow when you want it done yesterday.

Have you taken to drilling out the fuel passages in the air horn (top section) from where the fuel enters from the fuel line to the needle and seats?
(Picture below for reference)

I was asked about this a few times. I haven’t add it there yet. I don’t know what the inner diameter is and how far it can be enlarged. Once I knock out the plugged ends, I can figure it out. I also figure a set screw would work in place of the pressed in plugs.

I myself haven’t approached a limitation on the carb, so, this mod may not be of any actual benefit since the needle and west control the fuel afterwards. But a generous amount of fuel available there would insure a good continued supply to the needle and seat. It would take a good deal of consumption IMO to need a larger supply to the needle and seat. Probably out stripping the actual feeding capabilities of the needle and seat to need a larger fuel supply.

image.jpg
 
Rumble.
No, have not enlarged those fuel supply passages. I see no flow restriction. For a couple of reasons. The passages are already much larger than the biggest n/seat you can fit [ 0.120" ].
The entry passage is huge & the branches to the left & right fuel bowls are at least 9/32" [ 0.280" ]. This fuel is delivered by pump pressure, not gravity, so I see no need to enlarge the passages.
 
Bewy said:
Rumble.
No, have not enlarged those fuel supply passages. I see no flow restriction. For a couple of reasons. The passages are already much larger than the biggest n/seat you can fit [ 0.120" ].
The entry passage is huge & the branches to the left & right fuel bowls are at least 9/32" [ 0.280" ]. This fuel is delivered by pump pressure, not gravity, so I see no need to enlarge the passages.
Click to expand...

Thanks. I can’t say I have had a particularly power mill under a TQ yet. Moving a 3700 E body Cúda into the 12’s is a nice street engine but I did t feel the TQ was taxed on top of the 360 ether.

.280 inside diameter is healthy enough I guess. IDK personally. But I was interested to know. Just haven’t cut one up for it yet. Like you said, the needle and seat is the smallest restriction in the path way. While off hand I don’t know what the needle and seat are capable of flow wise, so long as there’s adequate fuel supply and pressure there it’ll be fine. That’s what I think my questioner was worried about. The mention of more fuel at the needle and west was mentioned.

That’s where I had to throw in the towel and said, I, myself never had a problem there nor did I know of anyone that did. Even with 90* turn passage ways, it’s always been fine. Though, again, I feel that I haven’t taxed the system yet. With a 3/8 fuel line to the carb, it’s a lot fuel available. A 3/8 line can provide enough fuel for a pretty darn powerful engine.
 
Yeah, sorry, I know tried to empty it. Had my son in law try to do it, a computer whiz kid, & he couldn't figure it out.
 
Here is one change I have made in preparation for continuation of dyno testing. Air door adjustments by bending the metal flap is not a good approach IMO. So I made an adjustable screw using a cut #4 screw nut coupler, a #4 set screw and a jam nut. I used solder to attach it to the existing metal tab. I tried marine tex epoxy but it would not adhere well enough.

20231126_150537.jpg


20231126_150622.jpg
 
Bewy said:
Yeah, sorry, I know tried to empty it. Had my son in law try to do it, a computer whiz kid, & he couldn't figure it out.
Click to expand...
Bewy, I left a reply that got wacked.
 
Rumble,
I thought I had deleted the 15 PMs. Obviously not. I got the 15 conversations on the screen but have had no luck deleting them.
 
Bewy,
I understand all the mods except the one about just cutting off the bullet ends of the discharge tubes, not sure which ones are the discharge tubes, the ones just oustside the secondary flap housing, east and west, ,with the bullet shaped ends ??
 
Yes, those. Each sec bore has a long 1/4" brass tube sticking out of the air horn. Cut off the bullet ends, at the angle shown.
 
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