I have spent several days now trying to get the carb on my Bronco adjusted correctly. '68 with a stock 289.
Using a timing light with tach and a vacuum gauge, I have set the timing correctly, adjusted the idle mixture screws until I have the highest steady vacuum, and used the regular idle screw to set what is supposed to be 700 or so RPM. All of this has been done with the engine at normal operating temperature.
At highway speeds, the Bronco pops wheelies. Accelerating onto the freeway has plenty of power. Idling on my driveway the vacuum is not perfectly steady but has a small needle sweep between 15 and 16 pounds.
If I have the idle set around 700 RPM (according to the tach there is a 40-50 RPM fluctuation as the engine is idling) and then rev the engine or go for a drive, when the engine returns to idle speed, the idle is now at 550. If I adjust the idle speed screw so the RPMs are back up to 700 then again rev the engine for a bit or go for a drive, the RPMs are then at 950-1,000 when the engine returns to idle speed. Then I have to set the idle speed screw back down and this whole thing starts all over.
Driving around town, half the time the Bronco idles decently, other times it wants to die. If I bump the RPMs with the screw and keep driving, sometimes the idle is OK, other times it's way too fast. This is just driving around town, not shutting off the engine, just stopping for lights and stop signs.
What on earth would cause the idle to fluctuate after driving here and there and/or revving the engine for a bit on the driveway? I can't seem to get it to idle smoothly but freeway driving is great.
Am I fighting a tiny vacuum leak?
Using a timing light with tach and a vacuum gauge, I have set the timing correctly, adjusted the idle mixture screws until I have the highest steady vacuum, and used the regular idle screw to set what is supposed to be 700 or so RPM. All of this has been done with the engine at normal operating temperature.
At highway speeds, the Bronco pops wheelies. Accelerating onto the freeway has plenty of power. Idling on my driveway the vacuum is not perfectly steady but has a small needle sweep between 15 and 16 pounds.
If I have the idle set around 700 RPM (according to the tach there is a 40-50 RPM fluctuation as the engine is idling) and then rev the engine or go for a drive, when the engine returns to idle speed, the idle is now at 550. If I adjust the idle speed screw so the RPMs are back up to 700 then again rev the engine for a bit or go for a drive, the RPMs are then at 950-1,000 when the engine returns to idle speed. Then I have to set the idle speed screw back down and this whole thing starts all over.
Driving around town, half the time the Bronco idles decently, other times it wants to die. If I bump the RPMs with the screw and keep driving, sometimes the idle is OK, other times it's way too fast. This is just driving around town, not shutting off the engine, just stopping for lights and stop signs.
What on earth would cause the idle to fluctuate after driving here and there and/or revving the engine for a bit on the driveway? I can't seem to get it to idle smoothly but freeway driving is great.
Am I fighting a tiny vacuum leak?
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