My first post here...I've got a 26 coupe that I inherited from my father (who bought it in 1949!) that had a complete pro engine rebuild about 15 years ago and has run like a top since, every time I've driven it. Recently, however, the car has been running rough in second (high) gear and is down on power...it hesitates and misses occasionally and is just not smooth. It starts and idles fine, and has good power and is smooth in first gear.
Last month I had the car in a vintage car shop to get the rear axle seals replaced, and they went around the lubed and oiled everything. This symptom started on the drive home from this shop, and in fact seemed to begin when I turned the key from BATT to MAG while cruising down the road, which caused a backfire through the exhaust, which it had never done before. Right after that it seemed to start running rough. Maybe that's just coincidence. I had it out a few weeks ago and it was running rough, but then it suddenly cleared up as I approached home, so I thought some dirt in the carb had passed,and I was set. Got it out yesterday and the rough running is back.
I first suspected bad gas or water in the fuel and have drained the tank and checked the sediment bowl. I have good fuel flow from the tank. I never buy E10 fuel.
I'm guessing it's time to clean/rebuild the carb? I recall my dad doing that once in awhile. Car seems to have the original Holley BN carb.
But thought I'd check here first in case I'm missing something obvious. He taught me a lot about this car but not everything...
is your timer clean?
are the plugs fouled?
Did you try to adjust the mixture?
are all four coils buzzing?
Plugs look great (light gray), but are 10 years old and could be replaced.
I have played with the mixture from the dash.
Coils are buzzing.
Note that the shop that fixed the axle seals did apply oil to the commutator through the little port. I considered that might be an issue but those guys are experienced pros and told me it takes just a few drops.
A drop of oil does not fix a worn out timer. Please remove the timer and photograph the insides for us.
The simple fact that the coils buzz does not indicate a good timer.
Sudden and intermittent makes me wonder about carbon tracking in the coil box wood or maybe a coil going bad. I had a coil I had just rebuilt that was intermittent. I found a bad connection where the primary wire attaches to the bottom contact button. A little solder did the trick. I imagine an open, but arcing secondary might be intermittent, as well.
What condition is the ignition switch in?
Clean, inspect and re-oil the timer. The timer roller should be round, smooth and turn freely. The roller track should be circular and smooth. A worn timer will usually have cupped out spots around the roller track and may be grooved. Make sure its seated correctly in the recess. My guess is the shop over lubricated the timer, or knocked a wire partly loose or otherwise messed it up a bit.
As Jerry suggested, post some pictures of your timer after you have cleaned it. You will get a good timer diagnosis then.
You could also look for a high voltage arc over by running it on a dark night with the hood up and taking a good look.
You might also check the manifold clamp bolts and see if they are tight. If they are loose, your backfire may have caused a leak in the intake.
I had my car at the Ellsberry Mo steam show this Saturday. It was running poorly from the parking lot (cow pasture) to the entrance gate. It actually died before I got inside. Somewhat embarrassing! I checked the fuel It was coming out of the bowl. Adjusting the needle didn't help. It died again when I did that.
I shut the fuel supply off and removed the bowl from the carburetor. With a needle nosed plier, I pulled the float pin and removed the float and the needle.
Mind you I was doing all of this in a crowd of people laying on my back with one guy video taping my activities too. My friend Joe Hauser was sitting in the car with his foot on the brake pedal the whole time too.
I went around to the back and turned the gas on for a second. "Anything coming out up there?" I asked the guy with the camera. "Yea sure is" he replied. Well I hope I flushed out some crud and turned off the gas. I wiped the needle on my pants leg, pushed it up into the carburetor, did a real fast shuffle with my finger and the float and got the float into position, picked the float pin up off of the crescent wrench handle where I had put it and I slid it into place like I knew what I was doing. Next I got the bowl back on and turned the gas on, ran around front, pulled the choke wire and gave it a spin, oops looked through the windshield to see that the spark was up, it was two more cranks and it started!
Now I told you all of this so I could tell you the rest (Pardon me Bill Cosby). The car ran way better after cleaning the needle and seat! How about that folks. Joe's foot was getting tired so I got in the car, looked up through the crowd and went about twenty feet to the entrance gate where they waved me in and I proceeded to find a spot to park after I found out I was going the wrong way in a parade. (That is another story)I pulled over to let the steam traction engine pass by.
My point is that your problem might just be a speck of dirt in the carburator.
My mag post nut got loose on the last tour causing loss of power and missing. I also found the nut on the back of the switch that the mag wire goes to was loose. Did your car run better on mag before this occured? Maybe the coils are not tuned to run on magneto. Are they old coils with original capacitors? Has the set been tuned on a hand cranked coil tester? Did an old original capacitor decide that now is the time to fail? I'd try the car with a known set of good coils and see how it runs, once you make sure the electrical connections are tight. Although the problem may be carburetion, it may also be electrical.
Charles, the back fire was probably caused by not moving the switch fast enough and the gas was open to allow fuel to continue to feed the cylinder without a spark until you engaged the mag. Does it run better on battery? If so, I suggest you have a weak mag at travel speed, or perhaps a bad switch, or lint on the mag pick up.
Applying oil to the commutator (timer) won't clean it. If you have a roller timer it needs to be cleaned every thousand or so miles, less than that if it has no grease in it. This might take 5 minutes of your time if you are slow.
Here's a link on the method of cleaning a timer. You don't need to disconnect any wires, but you will need a new cotter pin for the timer rod. You will also need a small piece of scotch brite, a rag, some solvent, and some grease.
You've gotten a lot of good advice here, all at once, like a shotgun blast. My suggestion is to be methodical about it by doing one thing at a time. I usually start with checking either the easiest thing first, or the most likely thing first. To me, the timer is your best place to start as it's easy to check and a very common cause of your trouble.
Hope to hear back from you soon.
I agree with Jerry. It would be unadvisable to tear into the timer, coil box, ignition switch, coils, and carburetor all at once. Do each one at a time and test the car afterwards. If something gets better or worse at least you'll have something to focus on. If you mess with everything in one shot, you may be left with a vehicle that won't even start and no clear idea of what to do then.
After reading all the above posts, I began to think,"What changed when you took the car to the shop? The only change you mentioned which would affect the running of the engine, would be the oil in the timer. So that's where you should start. Be sure the timer is clean and everything is smooth inside. Then turn on the ignition to batt and very slowly turn the crank. You should get one coil to buzz at each half turn of the crankshaft, or all 4 should buzz in sequence with two complete turns of the crank. If one or more don't buzz, you can then swap the coils thereby see if the problem is in the circuitry or in the coil itself.
Cleaning the timer will most likely fix your problem.
The backfire was caused by turning the switch while driving. It's best to turn it at idle before you start driving or at least back off the throttle and put it in neutral while switching. I don't think the backfire would cause it to run rough unless it caused a leak in the manifold to engine gaskets.
Does it run the same on battery as it does on magneto?