Classic/Antique Car Repair: 1954 Chevy Pick-up, valve lifter, stethascope

Question
OK, I changed the oil and spark plugs this weekend.  Oil was black and did smell like gas, spark plugs were jet black.  The original noise was at the top of the motor but after changing the oil & plugs, that noise went away.  There is still a slight mechanical sound (tapping sound like a hammer hitting a tack) I can hear using a mechanic's stethascope, in the back of the engine (towards the cab) and most clearly from the exhaust port.  I can hear it better in the cab than in front of the engine.  It does increase in frequency with rpms.

The rest of my homework:  It is a manual choke and I've learned not to use it. Got reprints of both the original Owner's manual and service guide.  Man!  What a difference in Owner's manuals from today.  No wonder we don't know jack about vehicles anymore.  Now they just tell you what the lights and buttons do and the rest are CYA warnings not to be stupid.  These old manuals actually told you what the heck those things under the hood do.

Thanks for all of your help, I greatly appreciate it!  

Answer
If the truck will start happily without use of the choke, even though the engine is stone cold, the carburetor is set too rich, and that is contributing to the gas getting into the oil, so you need to get someone to check out the carburetor settings - it shouldn't be that way - it should refuse to start when cold UNLESS you use the choke as I described before.

The tapping sound that went away was probably a misadjusted or stuck valve lifter, and it might have gone away because you changed the oil and got that gasoline out of there.  

The noise you still hear now could be an exhaust leak at the exhaust manifold - that can sound like a tapping too, especially if it gets much louder when the engine is pulling hard, and goes away totally when you coast.  It will also probably be worse when the engine is cold, but it wouldn't hurt to have a mechanic listen to it and confirm it. If that's all it is, it isn't going to do any harm, if it isn't too outrageous a noise.   It might require a gasket replacement to get rid of it, or it might mean the exhaust manifold needs to be machined flat due to warping from heat or age. It could also mean there is a crack in the manifold - none of those things are particularly bad, other than the fact that you might smell exhaust in the cab. If you do, get it fixed before you kill yourself!

You're welcome, and take care.  Stay warm this winter!

Dick