Mystery
 

29 Ford, rebuilt engine, all four plugs firing BUT it's got a skip almost like one of the plugs isn't.
Any suggestions appreciated.


Paul in CT

Re: Mystery
 

Vacuum leak on one cylinder, low compression on one cylinder, bad plug that looks OK out of engine put is not under compression. Bad distributor housing.

Use clear plastic cap to see if there is one cylinder not consistently firing. Try all new plugs. Switch plugs around to see if miss follows plug. Search for vacuum leak using starter fluid or hose to ear. Try to find bad cylinder by shorting out one plug at a time. Take compression readings. Try new condensor. Try new wire from coil to distributor. Try new distributor housing. Clean and adjust points.

Could be carburetor. Try different carburetor.

Re: Mystery
 

Does the "skip" occur at idle, under load or.....?
If under load, I'd look at the distributor top for the infamous #3/4 cross fire, condenser or even a bad plug.
This has the potential to go in a hundred different directions.

Re: Mystery
 

Change your plugs!!

Re: Mystery
 

How fresh is the rebuild? Did the skip all of a sudden just appear or did it start doing it gradually over time? If it’s a recent rebuild, it’s less likely that it’s a valve problem but it’s worth checking. You can do a quick check by holding a piece of paper in front of the tailpipe at idle. The paper will flutter a bit normally but if you see it get sucked back against the pipe you might have an exhaust valve hanging open too long from sticking or lash adjustment.

Re: Mystery
 

Check the point gap. if the points close up, the points arm can short to the cam intermittently. Reset them to .020. After, check that the rub/follower block is not too worn leaving the arm too close to the cam.

Re: Mystery
 

New cap, points, plugs, connectors. ALL plugs fire.
The "skip" is consistent.


Paul in CT

Re: Mystery
 

Can you isolate the "skip" to one cylinder?

Re: Mystery
 

If you tested the plugs by laying them on the head then one or more could still be bad under compression. Compressed air makes it harder for the spark to jump the gap.

Did you install a new distributor housing?