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I have brand new Chev 454 with just 1500 miles on it, I am experiencing extensive after-running (deiseling) on shut down SOME OF THE TIME! My local Chevy dealer (not the dealer that installed the engine, they are 800 miles away) says fixing it is not covered by my 36,000 mile warranty. What could cause this worrysome problem? Seems like I paid enough for the engine and shouldn't have to pay to get it working right.
What is your curb idle set at? Allso What is your engine temp. ? What kind of gas are myou using?To me it sounds like the engine is running to hot.Or the curb idle is set to high.I've worked for GM for 15 years,If they installed this motor and its been doing it sence take it back and demand they fix it right.
Look on the side of the carburetor where the throttle linkage attaches. You should find a solenoid there with a plunger that extends when the key is on and the throttle is opened slightly. The end of the plunger is hex shaped so you can turn it with a wrench. That is how you set the hot idle speed. The other large screw on the linkage is to set the idle shut-off speed, really it's there to prevent the throttle butterflys from seizing in the throttle bores. The purpose of all this IS to prevent run-on. To check just what/how the dealer's shop that installed the engine set the adjustments,warm up the engine, remove the air cleaner, plugging any open vacuum lines, and start the engine, holding the throttle slightly open.. Next, remove the wire from the solenoid, the throttle return spring should push the plunger back into the solenoid, the idle shut-off screw should contact its stop, the engine speed should drop way off, possibly even stall. That's how its supposed to work, anything else and you're going to have run-on.
Thank you Jim. Any leakage of air into the intake system will also cause run-on. Look for leaky gaskets, vacuum hoses, and if everything looks OK, check for wear in the bores for the primary throttle shaft where it goes through the sides of the carb. The shaft bores can be bushed with jewelers bushings if need be. Those old 4 bbl carbs are getting pricey when you can find them.
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