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1976 Chevy Truck Idling Too Fast
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TravisH
User
Jun 15, 2016, 9:00 PM
Post #1 of 2
(1431 views)
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1976 Chevy Truck Idling Too Fast
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I have a 1976 Chevrolet 1/2 ton truck and I have a question. It had a 350 V8 with automatic transmission. I just recently installed a re manufactured 2 BBL Rochester carburator it started out fine running good but now it idles too fast and it also the transmission shifts hard from park to reverse or drive. Put a vacuum gauge it checked out put a tack on it read 1800 RPMs. Studied my manuals but thought better ask someone first before going any further.
Thankyou
TravisH
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 16, 2016, 1:19 AM
Post #2 of 2
(1419 views)
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Re: 1976 Chevy Truck Idling Too Fast
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Quote you">>I just recently installed a re manufactured 2 BBL Rochester carburetor it started out fine running good but now it idles too fast and it also the transmission shifts hard from park to reverse or drive.<<"
OK - A replacement carb in this case "rebuilt" you set the idle when you install these things. They can't know out of a box where it should be, just close enough.
It's up to you to know EVERYTHING else is NOT an issue. In good tune, no vacuum leaks and everything hooked up properly.
Out of box they are dry so you've run it so need to let it warm up till choke plate is off or straight up. If it wont that's a problem to fix. There should be power (12v) was common to use an electric choke heater OR may use exhaust heat to shut if off. If no power and is electric find out why is next.
Once warmed up then set the idle speed. Out of the box there's no way it's known where it should be so you do that. Go for about 700RPM warm and force it, engine off, hold throttle open a bit an push choke shut then let go of throttle - cable or if someone pushed gas pedal.
Now that's the cold fast idle which should hover around 1,800RPM but only cold and only till you tap the gas pedal it comes down once right away then to base idle when choke is straight up or off. How long when cold it will stay at a higher idle depends on how cold it began from but always first tap of gas pedal lowers idle enough to drive away even stone cold.
The transmission with just a high idle would slam into gear - no surprise there. There's also a cable for it at carb you should NOT have to adjust if just changing carb to the same one just rebuilt.
In short it should have said to set your own idle - #s I just said are about right.
Important: Do not touch the idle mixture screws! It's about the vintage they were capped off so you couldn't but rebuilt may not have caps and were set when rebuilt. No need to touch those and if you did say so and let's put those back where they belong - leave those alone except for cleaning not now as it's just redone.
Again - all other operating issues of the engine must be right and known first or fuss back and forth if fixing vacuum leaks or anything till if behaves as intended.
DO NOT USE CARB TO COVER ANOTHER ISSUE WITH HOW THE ENGINE RUNS. Just the idle setting once should be enough and only touch that again when you've changed something on purpose or fixed something that had altered its setting,
T
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