Author Topic: Choke Engaged - High Idle Speed  (Read 208 times)

cyber104

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Choke Engaged - High Idle Speed
« on: November 12, 2019, 05:58:50 PM »
For those of you that have stock (or properly operating Qjets) - what is a reasonable high idle speed.

I'm finally getting my choke working so I don't have to feather the throttle until it's warmed up in cold weather (between 35-45 degrees F)

I don't know what a reasonable high idle speed is because I've never had one.

1700 RPM - 2000 RPM?

Can't find a spec even in the factory manual.

Thanks,
Chris
1978 TA 4-Speed W72

Wallington

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Re: Choke Engaged - High Idle Speed
« Reply #1 on: November 12, 2019, 06:08:15 PM »
Do you have the emissions decal on the radiator support? All the info is on it for your engine.

oldskool

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Re: Choke Engaged - High Idle Speed
« Reply #2 on: November 12, 2019, 08:08:20 PM »
Guessing that would be best set, at the cold temp. Otherwise, it will just be a guess.

Some folks, like my wife, are not gonna wait for an engine to warm up. If you're that way, you don't want the engine running at 2000 rpm, when you put the trans in gear. But, if you're gonna let the vehicle sit 'til the engine warms up, something like 1500-1800 should be plenty. Then make sure it comes back to a reasonable idle, after the choke is no longer needed.   

I'd thought about riggin up an electronic fast idle solenoid, with a toggle switch, to hold the idle speed up, when needed. I think the original purpose of those was to keep the idle speed up, while the AC compressor was kicked in.
« Last Edit: November 12, 2019, 08:20:39 PM by oldskool »

737driver

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Re: Choke Engaged - High Idle Speed
« Reply #3 on: November 13, 2019, 02:48:50 AM »
The best working mechanical choke I ever had was on my 72 LeMans with a stock 350. The high idle was about 12-1300 rpm. As it warmed up , the idle would decrease to normal idle (700 rpm or so). Worked great as advertised. I believe the service manuals do have specifications for cold choke idle and how to adjust them.
Jim
1979 Trans Am- Heritage Brown -W72 (Pontiac 400) -4Speed-WS6
1972 LeMans Convertible
1977 Trans Am
1972 Firebird
1971 Firebird
1970 Firebird
1977 MGB  Roadster Convertible

cyber104

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Re: Choke Engaged - High Idle Speed
« Reply #4 on: November 13, 2019, 05:56:50 AM »
No decals on the radiator support - so no help there.

I know how to adjust it but I'll be darned if I can find an actual RPM recommendation in the manual - I have an original factory manual - perhaps I'm just not looking in the right place.

I'm gonna take and average between 737driver and Oldskool and shoot for around 1400.

It's 24 in NC this morning and about 45 in the garage - I'll pull the car out later and set it back - right now I'm around 1600.

Thx guys,
Chris
1978 TA 4-Speed W72

Re: Choke Engaged - High Idle Speed
« Reply #4 on: November 13, 2019, 05:56:50 AM »

81Blackbird

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Re: Choke Engaged - High Idle Speed
« Reply #5 on: November 13, 2019, 06:13:07 AM »
Even though I'm running a Quick Fuel the electric choke is set and the high idle is around 1200-1300.  I'm with Old School and 737Driver.  With cold oil and you don't want to be close to 2000.

cyber104

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Re: Choke Engaged - High Idle Speed
« Reply #6 on: November 13, 2019, 06:30:35 AM »
Agreed - 2000 seems way to high to me also - 1400 seems reasonable.

Wish I could find the actual recommendation from GM in the manual

I just remember how great the choke system worked on my '70 Catalina - surely I should be able to get the TA to behave in the same manner
1978 TA 4-Speed W72

cyber104

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Re: Choke Engaged - High Idle Speed
« Reply #7 on: November 15, 2019, 07:17:22 AM »
I went ahead and set the high-idle to 1500 RPM.  I got that recommendation from my Mercruiser Shop Manual lol.  My boat also had a 4 bbl Qjet on it.

Much as I tried I couldn't find any information in the GM Factory manual.

Chris
1978 TA 4-Speed W72

Steve B

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Re: Choke Engaged - High Idle Speed
« Reply #8 on: November 15, 2019, 07:48:37 AM »
Do you have the emissions decal on the radiator support? All the info is on it for your engine.

This may sound stupid, but Classic Industries carries reproduction emission decals.  I would imagine they're accurate, but I don't know for sure.  It says the fast idle screw for a '78 400 with automatic transmission(RY) should be set at 1800.  I might be way off base here...

https://www.classicindustries.com/shop/1978/pontiac/firebird/parts/emblems-decals/restoration-decals-tags/
Steve
1980 Trans Am, 400, TH400 auto

cyber104

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Re: Choke Engaged - High Idle Speed
« Reply #9 on: November 15, 2019, 07:54:52 AM »
Hey Steve - thx for the info - I'm guessing the setting for a 4-speed car (like mine) might be a bit lower since there isn't as much transmission "drag" when you put it in gear.

That said - I'm gonna give 1500 a try for now - I can always bump it up later if necessary.

Thx again
Chris
1978 TA 4-Speed W72

Maryland Bandit

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Re: Choke Engaged - High Idle Speed
« Reply #10 on: November 18, 2019, 07:27:26 PM »
900 at idle, 750 in drive. Choke fully open and warm. Did enough of them to remember the 403 emissions decal.

cyber104

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Re: Choke Engaged - High Idle Speed
« Reply #11 on: November 19, 2019, 07:12:29 AM »
900 at idle, 750 in drive. Choke fully open and warm. Did enough of them to remember the 403 emissions decal.

That's fine but you are talking about base idle.

This entire discussion was about the high-idle speed when the choke is on (closed) and the engine is stone cold - so I'm not sure why you are quoting idle speeds when the choke is open and the engine is warm
« Last Edit: November 19, 2019, 07:14:32 AM by cyber104 »
1978 TA 4-Speed W72

Re: Choke Engaged - High Idle Speed
« Reply #11 on: November 19, 2019, 07:12:29 AM »
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