Question about TQ secondary operation

Bewy said
I am a TQ fan, have used them since the 70s. Have a couple of Comp Series 850s & lots of production models. TQs were used on Aussie Ford 302 & 351 engines in the late 70s, all are 9000 series.
The question I have is about the sec discharge tubes, which are the same shape/size on the Ford carbs & Mopar TQs; bullet shaped tip with a small hole & various holes of different sizes along the length of the tubes. Size, position & number of holes can vary with carb model.
The question below I have asked on a few forums but have never got a credible answer.

[1] What is the significance of the hole position?
[2] Does the position mean that, as an example, the upper holes deliver fuel before the lower ones? Or the other way round?
[3] What determines the hole size?
[4] There is a large variation in sec jet size, with the same air bleed size, on Mopar carbs from 0.125 - 0.143". Blade opening & AV fully open is the same, so that does not explain it. Odd.
[5] The Aussie Ford TQs had a 0.029" sec high speed bleed, compared to 0.039-0.040" for Mopar carbs that I have measured. Some Ford TQs came with 098 sec jets, smaller than the 101 primaries!! Go figure. No wonder they got dumped for Holleys! The AV shape & WOT position & sec WOT blade position is the same on Ford & Mopar carbs, so that doesn't explain the very small jet size. The smaller HSAB might have some impact, but the area of of 143 is more than twice that of 098, so seems a big leap.

Hey Bewy! I'm not sure I can answer all the questions. But first I have to ask what "AV" stands for? Air Valve? And why are there lines through most of your text? My eye's are having trouble! Weird! Anyway, here we go...

~~[1] What is the significance of the hole position~~

A different hole position willallow the air and fuel with in the tube to mix longer or shorter as well as discharge in a different location, which may or may not have an effect on spreadingthe fuel in a better spot. Sorry, thats the best I can think off, so, the second half of the answer m ay have no merit.

And holy ****! I look up and now my text has a line through it! WTF? Hummmmmm

~~[2] Does the position mean that, as an example, the upper holes deliver fuel before the lower ones? Or the other way round?~~

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I think the lower holes discharge the fuel first, but at the speed of which the fuel is pulled out of the tubes under vacuum, or actually due to theair velocity rushing past the tubes drawing it out, I don't think this is anarea to split hairs on tuning though it is an interesting idea to get a high speed cam to see what and where and when the fuel comes out of the discharge tubes. As to see what is exactly going on and when.

[3] What determines the hole size?

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I think the carb and or engine engineers decided that one.

~~[4] There is a large variation in sec jet size, with the same air bleed size, on Mopar carbs from 0.125 - 0.143". Blade opening & AV fully open is the same, so that does not explain it. Odd.~~

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Thats true. The jet size is determined by the tuners of the engine and what ever emmisions standard there under, or not.

[5] The Aussie Ford TQs had a 0.029" sec high speed bleed, compared to 0.039-0.040" for Mopar carbs that I have measured. Some Ford TQs came with 098 sec jets, smaller than the 101 primaries!! Go figure. No wonder they got dumped for Holleys! The AV shape & WOT position & sec WOT blade position is the same on Ford & Mopar carbs, so that doesn't explain the very small jet size. The smaller HSAB might have some impact, but the area of of 143 is more than twice that of 098, so seems a big leap.

Click to expand...

The air bleed size is part of the tune. Americans of the time may have been under stricter levels than else where in the world. Also note that our trucks didn't need to pass the same test as the cars. So that is one thing. Also size of the engine, make, year, model of the car or truck can play a roll.

The jetting size difference mkaes sense because the primary needs to be bigger due to the rod dipping down into the primary jet to lean out the mixture. Under heavy acceleration, the lack of vacuum allows the rods to be pulled up en-ruchening the mixture. The secondary side is without any rods, so it just gets jetted accordingly. Nothing to figure! Just gotta know the carb and how it works and why.

Dumping the TQ for a Holley? What year? This may have been a surply issue since in america, there was no problems until the near end of the Carter Corp. when Chrysler started to use the Rochester carb until fuel injection was standard.