Rock Auto spark plugs mishap. I've got Autolite 26s instead of 24s. Issues? Worth replacing with 24s or motor raft?
nope. the heat range of the plug reflects the ability of the plug to retain heat. a slightly warmer plug will probably show no difference.
Just listen for any spark knock during driving, and engine 'run on' after shutdown. Hotter plugs can contribute to those conditions.
You might want to do a Seafoam cleaning; any carbon in the cylinder, if it's kept hot, will keep igniting fuel coming in. Hotter plugs can contribute to that. Get rid of the carbon, it makes run-on harder to sustain.
Idle being too high, and ignition timing too far advanced are most likely the problem - one range hotter plug can't cause that. But a high compression engine will do that if the octane rating is too low, causing you to reduce the timing to make it stop.
I agree with pmrphil , one range hotter plugs are not going to cause the run on problem. Definitely check base timing and curb idle. Hopefully you will find your problem there. P.S. you might try a tank of higher octane fuel just for shits & and giggles. The Wrench