The other day my flathead (1946 59A) powered 35 pickup started stumbling and missing badly after running well for over a year. It was hard to start and almost didn't get me home. It has the stock crab style distributor & coil. It was not running rich and the coil checked out fine. I had just changed my plug wires (Flathead Jack's 7mm) & plugs (Autolite #216). I attempted to fix the problem by changing the points (.015 gap) and condenser. I also set the timing using metal rulers (www.vanpeltsales.com/FH_web/flathead_engines_distr-timing.htm) as I was shown here last year. I also had to cut a heavy leather plug and glue it to my vacuum break plunger (the old piece was broken and jammed against the housing). I could not loosen the large nut that holds the piston & spring, but when I was messing with it I did change the break adjustment screws location. My engine is now running much better, but still stumbles between 1000 rpm and 2000 rpm. Above 2000 rpm she runs well and it doesnt seem to stumble. Is it the vacuum break adjustment that is causing my problem?
It could very well be the vacuum brake adjustment. I do not know what grade of gas you are using, but if you are running 87octane and are now also hearing a "ping", the brake adjustment is probably off. Stumbling, gas ping, and general response are common problems wihen the brake adjustment is not correct. This should not, however, have anything to do with hard starting. The vacuum brake is functional only under load. In case anyone was wondering, 59AB distributor adjustment is a pain in the ass. The only way of telling is by road testing. Increase/decrease the brake adjustment screw SLIGHTLY, and road test it. You need to repeat this step over and over and over until the motor is running properly.
The problem started with the plug&wire change, yes? Go back and look there--could a wire or two come out of the cap when the outer cap was put on? Could the rotor have been damaged? Is the cap fully seated in its groove? Are you 100% sure the firing order is right? Seems like the problem staeted when messing with the secondary ignition circuit, so that's where to look. And never assume new wires are indeed properly crimped and undamaged.
One of my plug wires had a raja conector that had worked loose and the coil wire was not fully seated. In addition my distributor points plate was not fully seated and the retention spring was not seated into its grove. I fixed all of these problems, reset my point to .014 and she still stumbles some now at 2000+ rpm under hard throttle. I think that I have to get the correct advance/retard adjustment. It is a bitch w/o the machine that the old shops used to use. I am just adjusting then driving, readjusting.......and so on, and so on. Hopefully I'll have her running correctly by the end of the weekend. It sure makes me miss using my timeing light!
Examine the inside of your cap carefully--the loose Rajah was likely your original problem, and the spark to that wire might have burned a track in the cap to an adjacent terminal. On the timing, if you set the initial timing right with the ruler method start with the screw adjust mostly OUT--screw it to the top of its travel by hand (if you turn it hard at the top you will pop off the spring seat on the screw), run it down a turn or two so you have a small amount of tension, and run it. If you get pinging, tighten more. I don't feel stumbling is likely to have much to do with this adjustment. Go back and look at the online timing by ruler instructions AFTER you have looked at your distributor rotation. My memory is that the direction for advance on this web page is WRONG, carried over from an earlier distributor with the advance adjust on the other side. If you turned the plate the wrong way until points opened....oy. Went and checked. The instructions ARE backward--note that they describe the adjuster as being on the right side, which is correct for '32-36 if I remember right. Usually correct timing will be very close to center scale. You want to adjust from a position several degrees retarded towards advance when you set it. Study the pattern of pint activity--firing point is when second pair opens in direction of normal rotation.
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