ThermoQuad Secondaries Not Opening All The Way

Dibbons · Monday at 1:47 PM

Getting ready to rebuild the 6139S ThermoQuad I plan to use on the '72 Satellite Sebring Plus 340/305 project (see thread: "Project Odyssey"). Well, took the carb out of the box it was shipped in and first thing I did was open the throttle. I found the secondaries would only open part way. Oh no!

After some looking around, I found some kind of wasp mud nest had been built into one of the secondary throttle bores. It was no problem to knock it out with a simple screwdriver. (I will be following the article on FABO that RustyRatRod posted on how to rebuild a ThermoQuad).

GTX JOHN · Monday at 9:18 PM

Mine are always only open 86 to 88 degree as
I have found that best for performance.

I believe why it might be is air flow over
Secondary emulsion tube is disturbed over
that amount which hurts power.

My .02 = For free!

Go ahead everyone feel free call me an idiot again.

Ceedawg · Monday at 9:34 PM

GTX JOHN said:
Mine are always only open 86 to 88 degree as
I have found that best for performance.

I believe why it might be is air flow over
Secondary emulsion tube is disturbed over
that amount which hurts power.

My .02 = For free!

Go ahead everyone feel free call me an idiot again.

John, it might also be for better distribution to front barrels, those’d being much smaller and secondary more to the back of intake. I wonder how the TQ would work if it was turned around backward?

GTX5877 · Monday at 10:21 PM

Q-Jets seem like 87 degree is the magic number...

Dibbons · Tuesday at 12:41 AM

GTX JOHN said:
Mine are always only open 86 to 88 degree as
I have found that best for performance.

That's the correct factory opening as manufactured. My problem as you can see was the wasp nest was only permitting the secondary system to open half-way.

Geoff 2 · Tuesday at 2:08 AM

There also looks like mud in the front air vent. The MP bulletins recommended [ for WOT ] the sec blades at 88* for a single plane intake & 81* for a dual plane. It is not always about total airflow, but distribution also...
Congrats on using a great carb.

Dibbons · Tuesday at 8:22 AM

Geoff 2 said:
There also looks like mud in the front air vent

Thanks, good eye, the same or another insect tried to plug that area also.

RJRENTON · 2025-04-23T17:50:43-0500

GTX JOHN said:
Mine are always only open 86 to 88 degree as
I have found that best for performance.

I believe why it might be is air flow over
Secondary emulsion tube is disturbed over
that amount which hurts power.

My .02 = For free!

Go ahead everyone feel free call me an idiot again.

The factory 's attempt to limit air flow to a maximum as determined by the vehicle manufacturer to be able to use one basic carb design on several different engines. GM's QUADRAJET did the same time be used in different engines...like the PONTIAC's OHC 6. Usually fixable by bending the secondary stop bracket to allow for full open secondary throttle plates although the gain in air flow is a negligible increase.......
BOB RENTON

GTX JOHN · 2025-04-24T00:09:49-0500

When I open the secondaries to 90 degrees,
even with changing the jets and Air Door openings
numerous times I lost significant observable HP.

However, of course I do not expect anyone to believe me.

Geoff 2 · 2025-04-24T00:48:28-0500

John,
I believe you. It is not always about total airflow, as many think....

ThermoQuad Secondaries Not Opening All The Way

Dibbons

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GTX JOHN

FBBO Gold Member

Ceedawg

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GTX5877

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Dibbons

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Geoff 2

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Dibbons

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RJRENTON

FBBO Gold Member

GTX JOHN

FBBO Gold Member

Geoff 2

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