MTFCA Forum

The 1919 roadster runs great, pulls hills no problem. Now for some reason, it idles rough. What to check first? It has a new Anderson timer and rebuilt coils.

What kind of carb?

I had that problem when using Autolite or Champion* spark plugs.

*The modern style, not the old style take-apart plugs.

I agree with Jerry, and or it could be something to do with your coils, sometimes caused by being loose in the box. You can shim them a little tighter with a Popsicle stick.

I forgot to ask, battery of magneto? If on Mag, classic symptoms.

Did it have a rough idle before the new coils and Anderson timer? All the connections tight going to the coil box from the plugs? I had an occasional miss on my 24 and checked and rechecked until I found the barely loose plug wire to the coil box.
I checked all the harder things over and over and overlooked the simple!

Ensure that Anderson is firing at 0,90,180, and 270 degrees. I had one that was 7 degrees off at 180 and 4 at 90.

It ran great with the new timer and rebuilt coils for the last thousand miles, now idles rough but runs great under load.

Put some Motorcraft or Autolite new plugs in it. Their inexpensive and see what’s happens.
I have I have Motorcraft in mine and it runs fine but all T’s are a little different. Champion X’s are fine for some but for others other brands work better. Everybody has their preference. That would be the cheapest thing to try next unless in could something in the timer.
Maybe try changing the coils position in the coil box. If it runs smoother it could be one of the plugs. Anything is possible with a T.