QuestionQUESTION: my motor runs great when it is cold but as it gets warm it starts to run poorly when it idles but good at higher rpm's the is significant carbon build up in the exhaust but no smoke like oil burning
ANSWER: What year is your car and what make? I presume it is a General Motors but the year and make will make a difference as to what emissions equipment the car has and will make a difference in the answer. Let me know.
Brad
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QUESTION: the motor is in my boat but it is a 1976 oldsmobile and it does not have any type smog equipment on it
ANSWER: Is that because it has been removed? If the engine is stock there should be an EGR exhaust gas recirculating valve) on the intake manifold. This device was a constant source of idle problems when that car was in it's early years on the road. It runs well when cold because it is on the choke but when warm the fast idle kicks down and allows the effects of a stuck in the open position to show it's effects. The valve and the carburetor are designed to run with the valve in the open position when the engine is turning above an idle.
Let me know if the engine is stock and we will go from there.
Brad
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QUESTION: There is a fitting for a valve but no egr on the manifold. the motor is stock with the exception of 30 over pistons. it also has a holley 650 carb, i just finished resetting the timing and it runs better but still idles rough
AnswerSo we have some modifications to deal with. The first place that I would look would be for a vacuum leak. It could be from the intake manifold or gaskets, a vacuum line, or the carburetor base. I check for vacuum leaks using a spray can of carburetor cleaner. With the engine warm and at idle spray the carb cleaner around all of the places that could be a vacuum leak. When the cleaner hits a vacuum leak the engine will change speed and probably smooth out. If there are no leaks re adjust the carburetor idle mixture screws. This is done by working with one of the two screws at a time. Start by turning the screw out (counterclockwise) until the engine looses speed. then slowly turn the screw in (clockwise) until the engine picks up speed and then drops speed again. Turn the screw slowly out until the engine reaches peak speed and stop and repeat the process on the other screw. Then re adjust the idle speed.
