Racing Fuel Systems

First question is about production 6xxx & 9xxx TQs.

At some point in the production, the air horn got an additional 'hump' for an enlarged horizontal hole/passage that connected the air spacer above the float bowl area to the rear of the carb. What is very odd is that the angled hole that this passage intersects is....1/4".......on both models. Why create a new casting [ $$$$ ] & enlarge one passage, but not enlarge the passage it connects too. Does not make sense. Anybody have any thoughts???

Second question on the Comp Series 850 cfm.
I have two, one has screw in jets, one has push in jets. The air horn has other differences besides the jet type. While the two rear float bowl vents are slightly different, both are only about 1/2" above the air cleaner surface. Production TQs have two 1.5" tall tubes for venting.
I am wondering with the CSTQ short vents if fuel could slosh out on a hard launch. Thinking about blocking them off & just relying on the single, front vent which is quite large in diameter. Thoughts?

I don't have much experience with Thermoquads but you got me interested. So I had one in the garage and opened it up. Also I looked at some pictures I took of one I did for a customer in the spring. I did see differences.

In your first question are you referring to where the arrows point in these pictures

Yes,
Those are the passages. The upper arrow points to the angled hole, which is 1/4" on both models.

The lower arrow points to the passage that intersects the 1/4" hole. On earlier TQs, the top of the air horn was smooth & this hole was drilled through this section, to intersect the 1/4" hole.

At some point in the evolution of the TQ a 'hump' [ for want of a better term ] was added to the afore mentioned smooth section. This hole is slightly larger than that in the smooth top [ early ] version.

This necessitated a new casting.

What doesn't make sense to me is that in both versions, the hole that intersects the 1/4" hole is considerably larger in OD than 1/4", so what would be the reason for this change?

If you are not familiar with the 'hump' version you can probably find one on E bay to look at.

This is a picture of the top side 9127s . The second picture of the last post flipped over. This is the larger hump you are speaking of ?
In the two pictures above you can see they are different castings looking at the area the lower arrows point to.

For the second question you could extend them.

Interesting that the 9188s carb I redid in the spring had one rear vent screwed on.

Yes, that is the infamous hump. The hole diam is bigger than the ones that do not have the hump. Go figure.....
Single rear vent. Why would that be any better/different than the dual vent plus more $$$$ for a new casting?

RG & others,
The 9188 carb pictured. Note it has the screw-on rear vent. Either side are two casting projections.
On the Comp Series TQ, the rear vents are where the 9188 casting projections are....& have no tubes inserted in them, so they only stick up about 1/2" above the air cleaner pad. Note that the area under the top of a TQ is all connected between the primary & secondary areas, all one space.
Thoughts on this:
[1] I would be worried on a hard launch that fuel could spill out of the rear vents.
[2] The single front vent on the CS model is part of the a/horn casting, quite large, a 7/16" drill easily fits.
[3] Thinking of blocking off the rear vents to stop fuel slosh. In view of the large front vent, cannot see any problems? The AVS carbs have a vent midway between the pri & sec, so do not see any reason to specifically have a vent front & rear, as long as the air space is connected [ which it is ].

Just FYI, the CSTQ takes idle fuel direct rom the float bowl, NOT after it has passed the m/jet. Very carbs I have seen have this, Weber DCOE & IDA & some Dellorto models. It might explain the smaller [ comparatively ] sec main jet size of the CSTQ.