Usually vapor lock will make a car hard to start, but it will run okay if you can get it started and going.
It could be your float level is wrong, the float could be bad, or it could be as simple as the fuel filter is plugged up with sediment from the gas tank.
Re the points: If you take the distributor cap off, can you see the points opening and closing when you crank the engine? Is the rotor turning? Does this car use a ballast resistor in series with the coil? If so, it can be failing. There’s not much to a points ignition system. If you’re getting voltage at the coil, the condenser is good, the coil is good, the points are opening and closing and the rotor is turning like it should, there really isn’t much left. Check to make sure all your ground wires are in good shape too, including the one that goes from the engine block to the frame of the car.
I would pull the distributor and check the drive gear. I had 6 cly Ford that run like what you are saying. Drove me and my Dad nuts for two days. The pin had broke and the gear moved a hair. My Dad drove it 100 miles like this. You say you now have no spark. If the gear is not spinning the rotor you will not get spark. If it checks out ok, then set the points again and spin the distributor and watch the points open and close.
There are a couple of things. First, start with the coil. With the car cranking, the - post of the coil should have 1/2 battery voltage. If you have a positive ground, then the + post will have the half battery voltage. If you get 0 volts, the coil is bad or the ballast resistor is open, or the points are not opening. If you get battery voltage, the points are not closing or they are not grounded or the wire is open.
The main jet in the carburetor is in the bottom of the bowl. Junk can get in there, out of sight and cause your high speed problems. Pull the top off the carb and use a spray carb cleaner with nozzle straw to spray right down into the jet, or remove the venturi and spray back through the main jet.
There are several possible causes. Install a vacuum gauge between the fuel pump and tank and run the engine at a fast idle for several minutes watching for an increase in vacuum that would indicate a restriction. Install a pressure gauge between the fuel pump and carburetor and test again looking for the pressure to climb. Some carburetors had a very small fine mesh wire filter at the inlet seat that can accumulate sediment.
Look at the wires in the distributor that connect to the points. The points are mounted on a vacuum advance plate. And because the vacuum advance plate rotates back and forth, the wires to the points can be flexed to the point where the wire strands inside the wire break and the points don’t fire the coil.
I would not underestimate the burned points as a symptom. Leaving the key in the “on” position won’t burn out the points. Even if the points were in the closed position and there were constant current flow through them, they shouldn’t burn out unless there’s already a coating of carbon or some other resistance there. Even then, I’m not sure that would burn them out. The thing that burns points out is the constant tiny amount of arcing as they’re opened and closed. That’s where carbon gets created. Not to be confused with material transfer due to a bad condenser.
Based on your statement that the points were burned out, I’m inclined to suspect that your problem is ignition related. The condenser should have prevented the arcing that burns the points. The condenser is basically just a capacitor that spans the point gap and prevents charges. If the dielectric is intermittantly failing via a high resistance short, that’d act as a short across the points, the coil primary would maintain constant current flow, and you’d intermittantly lose spark voltage. If it were partially blown through and acting as a resister in parallel to the points it could be effectively reducing the peak spark voltage and causing rough running under load.
I know this sounds too simple to be true, but try changing the condenser out.
Note that this is not suggested in lieu of the other suggestings, but rather in addition to them.
Once you do get this thing running again, be sure you’re using the correct gas cap. It might be possible that air isn’t entering the gas tank to replace the fuel that your engine is using, creating a vacuum and causing the engine to be starved for fuel.
I once had trouble with an old Ford that would fuel-starve a couple miles from the house, and then restart and run fine from then on. Turns out the alcohol in today’s gas causes the nitron float needle used in modern rebuild kits to get soft & sticky, and mechanical fuel pump pressure isn’t high enough to force the needle out of the seat after sitting all night, and the float bowl runs dry. Eventually the needle loosens up and stays free until the next morning’s restart. Since the rubber-type needle seals better than the OEM steel version, the solution is to just change all the viton carb parts more often, unless you have access to pure gasoline.
Like I said, I replaced the coil, points, condenser, and rotor, yet there still seems to be no spark… There is plenty of gas coming out of the jets in carb when I pump the accelerator so that doesn’t seem to be a problem - at least not in order to start it. Just no spark… Everything is hooked up exactly like when it ran fine a week ago.
I should take the distributor cap off and make sure there is not spark in the points, I suppose.
Check for voltage at the coil. There are 2 small connections on the coil. Check for voltage on the terminal that’s not connected to the points. You should see a few volts less than 12 with the key on and 12 volts while cranking. If you don’t get these readings, you may have a bad ignition switch, wiring problem, or bad resistor or resistance wire in the ignition circuit, depending on your readings.
This is still the 6 volt system so it would be 6 volts not 12 right? I have check for current with a continuity tester and with the key on there is current at both posts.
A test light should indicate current on the + side of the coil with the key on. At the - side the light should indicate current when the points are open but when the points close they ground the circuit and the light should go out.
I would suggest stepping back from the problem and regrouping your thoughts. Throwing too many fixes at a problem can make it harder to find the actual problem. If you have a good shop manual for the Merc., follow the diagrams. Sometimes I find wiring diagrams on line.
Starting from scratch would be a compression test to rule out leaking valves or rings.
If your flat head 8 has the odd looking distributor mounted in front, like my 32 Flathead, there is a ground wire that sometimes has loose or dirty connection. All electrical connections and grounds should be checked cleaned or replaced. Even Ignition switch can cause problem. Good luck. I know how frustrating it can be.
The 52 flathead distributor is not like the 32. It is a side mount on the front end of the engine. With, what I would consider, a “normal looking” distributor cap.
Alright, I have yet another concern about my Merc. The overdrive doesn’t seem to work… What I did to bypass the overdrive relay (it’s the original and didn’t seem to work) I hooked a toggle switch into the “system” and what I would do is turn the switch on when I reached a speed higher than 30mph to send current to the solenoid. It did seem to kick into overdrive when I rigged this up. However, now it doesn’t seem to work anymore… Is it probably a solenoid/governor issue? Is it possible to rebuilt these as I am almost positive they don’t make reproductions of these overdrive parts.
I don’t know too much about this overdrive, but am hoping it’s not a problem with the actual overdrive unit…
Are you getting power thru the switch? It had relay for a reason. If the switch is burn out (I think it is). You can get a 30 amp relay and wire that in. The relay takes the load off the switch. The relay you want can is just a standard relay. You will find them at most auto parts stores in the area were they sell wire and fuse’s.
Well, I finally got my Mercury back on Friday and now it runs like a top. It turns out the accelerator something or another was dented in at one point so it was just not working right. The small wire from the destributor to the coil was broken inside so that’s why it wasn’t gettting spark. But now the speedometer is giving me more trouble. It works some of the time, but sounds like it’s grinding and then at high speeds it starts whining and the needle swings from one end to the other. The odometer still turns as smooth as can be. What could be causing this - a dry speedo cable?