Packard Forum Index » V-8 (1955-56)

Thanks for all your comments and suggestions. All are appreciated. As an update, I have changed out the points, switched coils, and have gone back and forth on how the distributor sits.
So, back to basics, put back original (new) coil installed original points (also new). When doing so noted that the ground wire to the vacuum advance plate metal terminal end may have been in contact with the cam. (Not sure) but repositioned the wire terminal away from the cam. Removed number spark plug and replaced with a snug fitting wood tapered dowel. Cranked the starter. Plug blew out with a POP! Timing mark on vibration dampener just to right of TDC, and the rotor now points to approximately number wire on cap. Installed test lamp to negative coil terminal and ground. Turned engine clockwise with socket on dampener and watched the lamp go on and off as the distributor cam rotated. So far so good. I also had been having a problem with carbon fouling and ended up cleaning fouled spark plugs, thinking that the cause was a carburetor problem, but only recently discovered that the fouling had been due to incorrect spark plugs. Because of the fouling problem I thought that the combustion chamber would be carbon coated so I went online to search for combustion chamber cleaners. Bought a can of Liquid moly and put it in the gas tank. After running the engine fort a short time, it dieseled badly when turned off. Purchased a borescope. Saw that the top of the pistons coated with carbon, Went back to the internet. Found an article that recommended flooding the chamber with carburetor dipping cleaner. I followed the method outlined and used the bore scope to verify that most of the carbon was removed. Installed a new set of AC 437 spark plugs. Ran engine for a short time with no unsteady idle. I thought that my problem was solved, but no it was not, gone back to unsteady idle. So, I switched the carburetor from my 56 to the 55. The 56 idle is rock steady. The idle variation persists after the swap leading me to believe that the carburetor is not the problem. Now I have gone full circle and am right back where I started from. Bummer.
Happy

I don't think you want to put moly in the gas tank. As for carbon, some carbon is normal, and if the engine is in fairly good tune, just driving the car on the road will usually reduce carbon to normal levels. I'd avoid putting solvents into the cylinders. It's rarely, if ever, necessary and can do harm. Even a tiny air leak at any joint or device connected to the intake can cause erratic idle. A slight leak at any of the intake valves can do the same. Idle speed that is set too low will often lead to erratic idle. Bits of carbon or other debris can stick to valve seats and cause idle problems. Driving the car for a few tens of miles will often correct such problems, as well as lightly fouled plugs, sticky valves, and sticky rings or new rings that have not seated fully.

The importance of fresh gasoline cannot be overemphasized. Stale gasoline can cause any or all of the issues you are having. Gummy deposits in the gas tank may dissolve into and pollute fresh gasoline. Excess fuel pressure can lead to a rich condition at idle, causing irregular idle. Improper float level, leaking or sticky float valve, or defective float can do the same.

A note about idle speed. Remember the 350 RPM idle is in Drive, not N. Idle in N should be like 450.

Side note, I have a friend with a Model T that when cold sometimes runs on only 3 cylinders. But other than that it runs well and when it warms up a bit you get the 4th cylinder. Not sure what the problem is, I told him to just put some MMO in the gas.

Point is, if it runs fine when driving and you know the timing, advance, etc are working, I wouldn't worry too much on idle personally.