73-87 Chevy _ GMC Trucks > Fuel Systems and Drivability

Dies after driving

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86LG4T5:
1974 C30 454 carbureted.  What seems to happen is it starts and runs fine and drives fine.  After driving long enough for the motor to warm up if I let it idle too long the rpms drop and it dies.  Then it's really sensitive to any gas when I restart.  Like if I even touch the pedal it's not going to start for a good 10 minutes.  If I don't touch the pedal sometimes it starts right back up.  I'm wondering if the idle mixture is too rich.  Also I need to make sure the choke is turning off on its own. The idle kickdown works fine. 

My main question right now is, does anyone know how to set the idle mixture?  Maybe screw in the mixture screws to the stops and the back off a specific number of half turns?  It's a big rochester carb.  Thanks!!

bd:
How long do you need to crank the engine before it starts when cold after sitting overnight?

With the engine idling at operating temperature and the air cleaner removed peer down the carburetor throat with a bright flashlight.  Make sure that fuel is not dribbling from the main nozzles onto the top of the throttle plates.  If that checks okay, shut the engine off and count the number of turns to lightly seat each idle mixture screw.  Record the results to establish a recoverable reference point.  Back each screw out exactly three turns and start the engine to check the idle quality.  Adjust both screws the exact same number of turns as needed to achieve a good quality and stable idle. 

Post the results.

86LG4T5:
>>How long do you need to crank the engine before it starts when cold after sitting overnight?
Sometimes it fires right up.  This morning I had to give it two pumps of the pedal and then it caught pretty quick.

I may have just had a clue.  Testing it in the driveway where I could watch the choke I couldn't get it to die.  Until I pushed the brake pedal.  I have hydroboost and the seller said the power steering pump was recently replaced.  Pushing in the brake pedal drags down the idle.  If that's normal then maybe my base idle is just set too low.  The kickdown seems to have 3 idle levels.  First starting it's very fast, then after a minute I can pump the gas and it goes to a normal high idle, then when it really gets warmed up another pump drops it down to a low idle.  But it's strong, until I push in that brake pedal.  Also it's a manual if that makes a difference.

bd:
Does it have an idle solenoid and is it working?  Adjust the idle speed according to the specs printed on the VECI label under the hood.

86LG4T5:
>>Does it have an idle solenoid and is it working?
Yes it has one and is moving so I think it's working.

Reading different things I'm finding that if the powersteering/hydroboost isn't bled correctly it can cause this issue.  Looks like it's a long process to bleed it correctly.

How to Bleed   - Hydro Boost Systems Only

  1  Do not start the engine until the system is fully bled.
  2  Raise the front wheels off the ground.
  3  Turn steering wheel fully to the left.
 4   Fill fluid reservoir to “full cold” level. Leave cap off.
  5  With an assistant checking the fluid level and condition, turn the steering wheel slowly and smoothly lock to lock until fluid level drops in pump reservoir. If fluid level has not dropped, no fluid has moved through the system. This normally indicates a large bubble in the reservoir or pump. Until this bubble passes, no fluid will circulate through the system.
    — Do not turn the steering wheel fast as this will cause the fluid to overflow the reservoir. Trapped air may cause fluid to overflow. Thoroughly clean any spilled fluid to allow for leak check.​
    Check fluid constantly to ensure proper level and that no bubbles exist.
    — If you see any signs of bubbles, recheck all connections then repeat the steps above.
    — Fluid level should be steady (Rock Ram’s level will vary slightly).​
 6    Discharge the Hydro Boost brake unit by performing three full presses on the brake pedal.
    — Watch power steering reservoir for any bubbling, foaming or burping.
 7    Once foam clears, crank engine until it just catches and shut off.
 8    Discharge Hydro Boost unit with three full presses of the brake pedal.
 9    Repeat these steps until no air or foam is seen in the reservoir.
    — If brake pedal feels soft, spongy or funny, system is not fully bled.

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