engine problems

[1970mavinator]

1970 200 I6. Ok engine still runs and gets me everywhere I need to go, BUT, when my foot is not on the gas, the RPM's are bouncing like a jack hammer!! I have already played with the air and gas screws on the carb. Helps some but goes back to doing the same thing. My dad messed with the dizzy a little but I dont know if he advanced or retarded the timing. I do have an exhaust leak but I doubt that would be a contributing factor seeing as though There has been a leak long before this problem. Not very experienced at all in mechanics but learning, so thorough explantaion would be helpful thanx, Derek.

 

[64.5 TX Stang]

Manual or automatic, it could be a transmission/clutch problem as well.

 

[BIGREDRASA]

Has the carb been rebuilt? Could be the power valve, or dirt. Could be a leaking float, letting the fuel level rise too high, or a damaged needle valve doing the same. These carbs are easy enough to rebuild, and the kits aren't that expensive. Good luck.

 

[Anonymous]

the RPM's are bouncing like a jack hammer!!

First I would sugest checking the spark plugs. How old are your plug wires. Check for vacume leaks. Check inside the distributor cap for shorts & cracks. Oh, and all of the above. If you are going to check the timing, you need to disconect and plug the vacume advance, try 8 to 10 degrees advance.

 

[1970mavinator]

The carb was bought newly rebuilt from advance auto about one year ago. The plugs and wires are probably about the same age. Thanx for the help I will try the above mentioned ideas. Oh the car is automatic.

 

[BIGREDRASA]

Try wiggling all the vacuum lines, and listen for a change in speed. Better yet, get a vacuum gauge and connect it to the PCV vacuum line, and see what it's doing. Also, check the little hose that connects to the vacuum modulator at the right rear of the transmission. Need to do this from under the car.
I'm still suspicious of a bad carb float or needle valve. With the air claner off, look for excess fuel surging into the carb throat.