okay. i have a 68 special with a 350-2 in it. the engine is in need of a thorough tune-up at the least, and a rebuild eventually. so this question may become a moot point once one or both of the above are taken care of. but... on cold mornings (which aren't THAT cold here in south alabama, we're talking low 40's at night, mid-50's in the morning), my car idles very rough, will stall in about 15 seconds if i don't lightly push the gas pedal. this problem persists for about the first 5-10 minutes of driving, just until the engine warms up... some additional info: i have a (badly) cracked exhaust manifold on the passenger side, and not knowing how long it's been cracked, i don't know what kind of havoc that has wreaked on my valves. ou: my theories, ordered from best to worst case: 1) carburetor needs idle and/or mixture adjusted; 2) cracked exhaust manifold is the culprit; warped/bent/burned valve(s)... any thoughts? thanks, :blast: scott
Check the choke unloader diaphram on the side of the carb. When you set the choke with a cold engine the choke plate closes completely. When the engine starts, the vacuum diaphram should open the choke a small amount so the engine will run without loading up. If it doesn't work, you will get a rough idle until the thermostatic coil opens the choke fully. Hope that helps.
Scott, This is a picture of a 72 rochester 2 bbl. This diaphram should be "pulled in" with the engine running. Make sure it opens the choke when you start the motor cold. Another possibility is carburetor icing. At 40* or so and high humidity, ice can actually form in the carburetor until the motor warms up. Exhaust crossovers and thermostatic air cleaners lessen this tendency. Do you have the stock air cleaner and is it operational?? Good Luck.
I'd venture to say that it's definatley a bad choke. I just changed mine, it was like a $14 part to fix. Not a big deal. I also changed the choke thermostat coil, I figured why not take care of both.
my new to do list... thanks for the input and the pics...i hadn't thought about the choke but it does upon reflection seem the likely cause...i'll check it this weekend (or sooner if i can) and let you know how it goes... i do have the stock air cleaner, but whether it's heat/cool system works is an unknown... o No: :blast: scott
Scott, It is easy to check the air cleaner. There is a door in the snorkel that operates on engine vacuum. There is also a temperature sensor in the air cleaner base. One end of the sensor should be hooked to manifold vacuum, the other side goes to the vacuum motor on top of the snorkel. When you start the engine cold the door in the snorkel should snap closed drawing hot air from the stove on the exhaust manifold. When the motor is fully warmed up the door should open some to mix hot and cold air, and keep the temp in the air cleaner constant. You may need to use a mirror to see the door with the air cleaner installed. Hope that helps.
