QuestionI am not satisfied with how my sixer in my 67 runs. When the engine is cold it runs at slightly high rpms, which is fine since they cease once the engine warms up, but them once it's warmed up the idle becomes horrible. The engine does not sound 'constant' and makes a kind of "put-put" sound and vibrates the car whenever it makes the "put". Another explanation would be, it feels like whenever it fires i feel the engine torque the car, its very annoying and will stop when i put the car in park or neutral. Or if I hold the brake and give it a little gas, to match the "cold engine's" RPMs the shaking stops. Putting my hand to the exhaust you can clearly see and feel the put-put nature of this engine when a puff of exhaust comes out it forces my hand backwards in such a way that it makes it look like you can differentiate every piston firing. Any ideas as to what i can adjust or fix?
And also my brake lights don't light up unless i push VERY hard on the brake, how do i adjust this?
Thank you SO much for your consideration!
AnswerThe higher speed when cold is correct, that is the way it is designed to run, as the automatic choke on the carburetor richens the mixture and increases the idle speed to help the engine run until it reaches normal operating temperature.
The rough idle when the engine is warm is a common symptom of an engine which has one or more burned exhaust valves. There is no adjustment to make, the engine will have to be taken apart and fixed.
To determine that this is indeed the cause, have a mechanic perform a "compression test" on the engine, and if that shows that one or more cylinders are below specification, have him perform a "leakdown" test to determine where the compression leak is. I'm betting it will be at least one bad exhaust valve.
The cure for this is to remove the head and send it off to an automotive machine shop for repair. This will cost somewhere around $500, unless other problems are discovered during the operation, which may well happen, depending on how many miles the engine has been driven since the last rebuild, and also depending on how the car has been driven.
It is remotely possible that your compression test will show all cylinders in the normal range - if this is the case, your problem may be cured by having a simple tune-up done on the engine, with special attention to the carburetor idle mixture settings.
If you would rather not deal with this problem now, you can ask any mechanic to adjust your "hot curb idle" speed to a higher RPM - that will mask the problem for a time, although you will then have to deal with the car straining to move when you stop it in gear. This "fix" should be done free, as a courtesy.
Your brake light problem is caused by the brake light switch, which is in one of two places, depending on which brake system is on your car.
If you have a hydraulic brake light switch, it is mounted on one of the fluid lines under the master cylinder, it will have two wires connected to it. This type are cheap and easy to replace, and that is what you need to do, however it does take a special tool, so you may need to take it to a mechanic for that also.
If you have a mechanical brake light switch, it is under the dashboard, and is operated by a part of the brake pedal linkage pressing on a spring loaded push button. If you slither under the dash with a good flashlight and observe the action of the various moving parts as a helper presses on the brake pedal, you will spot the switch. You will find that it is mounted in an adjustable bracket; you can move the bracket so that the switch is activated earlier in the pedal motion travel, that should cure the problem.
Dick
