I have been helping a friend with his T he has only driven it one or two times each summer, the problem is it has a slight skip kind of runs rough when I ground out the plugs one through three you really notice but on four you can barley notice the difference, the spark is great, I pulled the side valve cover off and noticed on the number four cylinder that the exhaust valve when in the closed position there is no Clarence between the valve and lifter it seems to go up and down fine but it must be holding it open a small amount he said that it used to run good so I know at one time the valve clearance was there could the lifter be sticking?
It could be the valve or seat is burned or just plain worn. You will have to remove the head, remove the valve, inspect the valve and seat, then correct the defect as necessary. If it were mine I would do a full valve job. You can do all this in the car easily, if you have the right tools.
Do a Compression check first. That will tell you if there is an issue with the valves or cylinder. What spark plugs are being used? Install a clean set. Most issues I see when checking someones engine for running bad are due to spark plugs. Coils and carb mixture adjustments are right behind that.
Most people don't understand spark plugs and the flow of electricity. A spark plug can spark ok in the open air. But once under compression, the air gap is harder to jump and the electricity is going to take the path of least resistance. That path may be down the side of the insulator due to conductive residue, or it may be in the high tension insulators of coil box from carbon tracking to sheet metal etc...
Once again: compression test will tell. If #4 is low, and it might be only slightly lower if the valve is barely seating, a bit of oil in that cylinder and a re-test will tell the tale. If it doesn't rise an un-seated valve is a highly probable cause for it. Doing then all would be a +.
Be sure the lobe of the cam is pointing straight down when you check the clearance. If it is too tight, you may have a burnt valve and will need to do a valve job. If it has adjustable lifters, you could try adjusting it to the proper clearance and then check the compression. The compression should be nearly the same on all cylinders and between 40 and 60 psi.
I changed the number three and four spark plugs around, same result number four not running smooth, have great spark and new plugs, still puzzled as either the valve is coming down too far or the lifter not going all the way down there for sure is never any clearance between the valve stem and lifter at any time. I have to find a compression tester but I'm sure it's low on number four. This is a 1926 is there any adjusting the lifter?
The original lifters were not adjustable. The valve stem was ground to the desired clearance. However, many engines have been fitted with adjustable lifters when the valves or camshaft were replaced. You can tell easily by removing the valve cover behind the manifolds and looking for yourself. The adjustable ones will have a hex shaped top on them. The non adjustable ones are just round.