TAC Tech > Mechanical

The Choke Thread

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DeVilliers:
Since this is the choke thread.........

Where is the choke handle located under the dash? I'm busy putting mine back, but it now looks like the cable is to short, which it can't be.
My location is then wrong.

Thanks

roadking77:
I dont know motors but am pretty sure there is no manual choke knob at least on the later second gen trans ams. One may have been added by a previous owner though. I know a guy that put one on a 79 formula.

5th T/A:
I am almost positive that there was never a manual choke on any Firebird from the factory, so you will have to find a suitable place under the dash to mount yours. Or convert it to an automatic choke.

Wallington:
No manual chokes on US-based Quadrajets.

nUcLeArEnVoY:
I'm pretty well-knowledged on how the choke works at this point after two years of ownership, but I'm facing a bit of a dilemma with mine that I'm hoping somebody can chime in on...

My car is a 1979 400/4-speed, though most earlier years work generally the same: the hot air automatic choke, the intake manifold exhaust crossover, and the EFE/Heat Riser valve all work together to provide the best possible warmup in cold climates and minimize the amount of time necessary to appropriately vaporize intake manifold fuel charge for best cold-weather running. The exhaust crossover serves as a passage in the center of the intake manifold that runs under the carburetor - this passage interfaces on either side with ports on the cylinder heads that are open to the exhaust chamber, and exchanges exhaust gases between both cylinder heads and is the basis for which the stock hot air choke works. The EFE/heat riser valve, meanwhile, is a valve flapper located in the driver side exhaust manifold just where it meets the exhaust pipe, and the valve, at least for my model year, is vacuum-actuated and regulated by a thermal vacuum switch in the intake. From 0-140 degrees coolant temp, the heat riser valve receives a vacuum signal which *CLOSES* it, cutting off driver side cylinder bank exhaust from leaving the driver side manifold and instead forcing it across the intake crossover to escape the passenger side manifold and exhaust. This extra exhaust being forced across the crossover provides extra heat to warm up the intake, as well as further assist in transferring additional heat to the hot air choke tube that reaches into the passenger side cylinder head crossover. Once the coolant temp exceeds the calibrated temp, the vacuum signal is then cut off to the EFE/Heat riser valve, which OPENS it and allows the exhaust from the driver side cylinder bank to escape through the driver side manifold as normal. All three of these things work together.

Here's my issue: I'm doing an exhaust manifold gasket change on my driver side due to a massive leak I've been tolerating for 2 years. Covers my 1 and 3 plugs and temp sensor in soot, it's loud as heck... I'm sick of it. Anyway, I pulled the original heat riser valve and come to find out some idiot in the past actually welded the darn thing CLOSED. Yes, you heard that right. CLOSED. So my car has been driving with an exhaust restriction for Lord knows how long. Not a complete restriction - some exhaust makes it past the closed valve, plus the huge exhaust leak, and plus the exhaust was still able to at least go across the crossover and out the passenger side. It's a good thing I granny drive the car, I very rarely exceed 3200 RPM since no matter how tempted I am, I can't ever feel 100% confident with an engine so old.

Anyway, needless to say I'm gonna ditch the stupid heat riser valve and just gut the innards to turn it into a spacer. My current exhaust setup is stock manifolds mated to a true dual without cat(s), so if I had to have this restriction, at least all the other components were ideal to prevent catastrophe lol.

So since I'll be deleting the heat riser valve, my concern is, if it will delay the hot air choke from opening up. I *LOVE* how good my hot air choke is. I live in South Florida, so it's not like I need it anyway, but my car will start up after 3-4 seconds of cranking with just one pump of the pedal even after sitting for a week, and just after 3 or 4 minutes of fast idle, I can blip the throttle and be off the choke. I went through a lot to restore function to my hot air choke, the entire time not knowing that my heat riser valve was stuck closed and supplying excess heat and exhaust in the crossover even when the car was already at operating temp. I DON'T want to switch back to electric.

Does ANYBODY still use the factory hot air choke but deleted their heat riser valve? Like maybe you use the hot air choke but have headers installed? I just want to know if the loss of the heat riser valve will make that much of a difference with how quickly the hot air choke opens. I'll still have an open crossover, it's just I'll be depending on exhaust gases to exchange across it via normal turbulence rather than being forced by the closed heat riser valve. Again, I DON'T want to go back to an electric choke.

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