When I took the spark plugs out on my 1923 T I found that they were very sooty and black, indicating that the engine was running too rich. It appeared to run well and once the engine had warmed up the dashboard control for the NH carb was set to the "sweetest" position. Is there any other adjustment for richness, or any other reason why it should be so sooty?
How does the exhaust look? No smoke? Black smoke or blue/white smoke?
Are all cylinders the same sootiness?
It's probably sucking a little oil.
It isn't necessarily noticeable at the exhaust but still burning a little oil.
If everything is, or has been, OK I wouldn't over analyze it........
The carburetor mixture adjustment is not equally effective at idle as it is at speed. So perfect mixture adjustment at 30 MPH might make the engine quite rich at idle. Or not.
Many of the modern spark plugs are inappropriate heat range for a Model T, so those often are very sooty looking and foul easily.
The exhaust is only smokey when first starting up, after that it is fine. All plugs are the same sootiness. What plugs would you recommend?
Soot comes from running too rich, as you know. Running to rich comes from running too cool. Most people fix that with the hottest and most expensive plug around, the Champion X.
I prefer a thermostat, and whatever plugs.
rdr
Running TOO rich, not: to rich.
Wish we could correct our posts.
i find mine needs to be richer at idle than it does at speed.
Along the same line, but different. Tuesday I drove to the bank which is one mile down hill. Then to the barber shop about 1/4 mile from the bank, then to the post office about 1 1/2 mile down hill from the barber shop. From the barber shop to the post office I did not stop the car until I got home which was all up hill from the post office. The motometer was at "normal summer temperature" when I got home. I wanted to get out another Model T and then park the one I'd been driving in it's place. I left the warmed up T idling in the driveway while I started up the other one. It took longer to get it started than I thought and the T idled for about 5 minutes. I noticed a cloud of black smoke coming out,I think the exhaust, so I turned it off. After I got the second T started, I started up the one which had been smoking, I tried adjusting the mixture but it was still at the "sweet spot", and drove it in and parked. It was still smoking when I parked it. Haven't tried to run it since. It doesn't usually smoke. What could have caused it to smoke? It has a Holley NH and a Anderson timer.
According to brass car guru, Harold Sharon, most modern plugs are too cold for our cars. Champion-X plugs are reputed to be good, hot plugs and they're designed for just our kind of engines. That having been said, I have the same problem as you, Ian, and switched from Motorcraft F11 plugs to Champion-X plugs only to find they made the engine run badly. I put the F11 plugs back in, got my performance back and started to pay more attention to my mixture control.
I've been given to understand that our little, cold-blooded 4-bangers prefer a richer mixture for starting and warm-up (as most engines with a choke control do), but benefit from leaning out the mixture once they warm up. My car has a flat-tube radiator and the engine takes forever to get the red "mercury" to pop up into view on the Motometer's thermometer.
This is an unsurprising reminder that short trips are bad for all car engines. Ideally, they need to be warmed up, leaned out and run fairly hot for a fairly long time to get the carbon off the plugs and out of the cylinders, and the water and sulfuric acid (both are combustion byproducts) out of the oil.
StarTron fuel treatment's advertising claims to clear carbon out of engines. You pretty much need this or a similar additive to keep the ethanol-tainted crap, which with unbounded imagination and optimism we refer to as gasoline, from separating like salad dressing and going stale in a car that isn't driven frequently, so perhaps this is at least a partial remedy.
http://mystarbrite.com/startron/
I use StarTron too, and I am now in the process of putting my "modern" car (1952) into hibernation for the winter. I emptied the gas tank and went to the local marina and bought enough ethanol free
90 octane marine gasoline to fill the tank and run through the fuel system.