1953 Mercury unusual plug condition

[Merc Cruzer]

This question is about my 53' Mercury with a stock flathead engine, and the original stock distributor, along with the original stock Holley 1901 Teapot carb.

Plugs 1,4,5,8, are burning normally and clean, but plugs 2,3,6,7 are burning rich and black. To restate: the 4 corner plugs are burning normally and the 4 center plugs are burning rich.

Has anyone run into this situation? If so, what was the cause?

As a side note, the car runs fine.

Thank you,

Roy

[petehoovie]

Originally Posted by Merc Cruzer

This question is about my 53' Mercury with a stock flathead engine, and the original stock distributor, along with the original stock Holley 1901 Teapot carb.

Plugs 1,4,5,8, are burning normally and clean, but plugs 2,3,6,7 are burning rich and black. To restate: the 4 corner plugs are burning normally and the 4 center plugs are burning rich.

Has anyone run into this situation? If so, what was the cause?

As a side note, the car runs fine.

Thank you,

Roy

[Bill OH]

I would find a diagram of the runners of the intake manifold and I am of the opinion that one of barrels of the carb is feeding too much fuel. I would take a look at the main jets for size - do not think it is float level or defective power valve. - float level and power valve affect both barrels. Take a look.

[aussie merc]

im with Bill loose jet or blocked emulsion tube

[Merc Cruzer]

Sounds like a good place to start.

Thank you,

Roy

[tubman]

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"If it ain't broke, don't fix it". If the black plugs become a problem, replace them with plugs that are a heat range or two hotter.

[38 coupe]

This sounds odd to me. If one side of the carburetor was running rich you would have sooty spark plugs on two outside cylinders on one side of the motor and the two center cylinders on the other side of the motor. All inside cylinders rich is both barrels of the carburetor.

[ford38v8]

Originally Posted by 38 coupe

This sounds odd to me. If one side of the carburetor was running rich you would have sooty spark plugs on two outside cylinders on one side of the motor and the two center cylinders on the other side of the motor. All inside cylinders rich is both barrels of the carburetor.

Good call.

[rjlester]

I wonder if the exhaust crossover is plugged?

[Ross F-1]

Interesting that those are the 1st four cylinders in the firing order; could the cap be off-center?

[Merc Cruzer]

Originally Posted by rjlester

I wonder if the exhaust crossover is plugged?

I have duel exhausts, with the correct factory manifold, on the the drivers side.

[Merc Cruzer]

Originally Posted by Ross F-1

Interesting that those are the 1st four cylinders in the firing order; could the cap be off-center?

I checked and it is correct.

[38 coupe]

I like Ross's suggestion of ignition as the source. Have you checked the distributor for bushing wear or off center point cam? I ran into each of these problems on different distributors and had a heck of a time diagnosing the problem.

[Merc Cruzer]

Originally Posted by 38 coupe

I like Ross's suggestion of ignition as the source. Have you checked the distributor for bushing wear or off center point cam? I ran into each of these problems on different distributors and had a heck of a time diagnosing the problem.

I put new bushings in the distributor a few months ago, just prior to having it set up on a Sun distributor machine.

[Als48]

I worked on a tractor once, that had a distributor problem which sounds like this issue. It was running but only on two cylinders. I found the cap to be distorted or warped and was able to correct it by filing the portion that had to fit into the ID of the distributor more round. That allowed the cap to center up properly and the plugs to fire more evenly. The cap must have been canted slightly, causing the rotor to miss firing two of the cylinders. I scratched my head over that one for a day or two.

Al Hook

[Merc Cruzer]

I cleaned the plugs this morning and took it out for a lengthy drive. I had changed the timing a coupe of days ago and wanted to see if the new timing resulted in additional power. Bottom line, it did. Previously I had done a series of short drives, involving steep hills to see if the new timing resulted in additional power. I am beginning to think the short bursts of acceleration, allowed the power valve to open, dumping additional amounts of gas into the the intake, yet not burning completely in the center 4 cylinders.

I live at 8300 ft and currently running 54's, for the two main jets. I will take the carb off later this week, to go through it and will change the jets to 52's, as that will serve to further clean up the plugs. The 4 corner plugs are good, but could be better anyway.

Thank you all for your suggestions and input.

[ford38v8]

Originally Posted by Merc Cruzer

…I live at 8300 ft and currently running 54's, for the two main jets. I will take the carb off later this week, to go through it and will change the jets to 52's, as that will serve to further clean up the plugs. The 4 corner plugs are good, but could be better anyway.

Thank you all for your suggestions and input.

Merc, at 8300 ft, less oxygen should translate to less fuel. Using .054s for jets does the opposite. Ford’s sea level jets were .050, no wonder your plugs are sooty.

[Bored&Stroked]

Given you're talking about plugs, coloring, etc.. How are you actually checking them? You can't just drive it, hit some stops on the way back and pull the plugs in the garage - that will tell you nothing. You have to load test on the highway, push the clutch in and coast to a stop. Also, reading plug colors with today's fuel is difficult. I don't see "chocolate" colors anymore. So, I use an O2/AFR meter to actually tell me what is going on.

[Merc Cruzer]

ford38V8 and Bored&Stroked,

The speck for 53' Merc is Sea level = .056 and 5,000 to 10,000 = .054. Since I am currently running .054 and it is still a bit on the darker side, I will give the .052's a shot. If that turns out to be too lean, then I will go back up to .053's. Lucky I have a nice collection.

Normally what I do, is take it out for a 30 mile drive on the highway. That allows the car to run at speed for a period of time and the return trip involved allot of uphill driving, with the engine under load. We are talking about climbing 3000 feet in 13 miles. At the end of the trip I pull the plugs to inspect them for color and fowling. Unfortunately, it is the best I can do.

Now as to your suggestion of: "You have to load test on the highway, push the clutch in and coast to a stop.", the closest would be shift it into neutral and come to a stop. I have a Merc-O Matic. The 02/AFR meter would be a great thing to have but, the cost is a bit prohibitive and I don't know anyone that currently has one. So unfortunately I will have to give it my best shot.

Thank you both for your input and suggestions, I appreciate your advice.

[ford38v8]

Merc, my mistake. I'm stuck in the .94 mode of thinking, not the Teapot. Your .054 jet size does make sense now. I hate to have unanswered questions, but Tubman's suggestion might be the way to go. Still, with the high altitude, that in itself may account for less vacuum on the longer runs, dumping a higher volume of fuel in the near cylinders. I don't know what I'm talking about, just a stab in the dark.