I have a consistent problem with my 76 Spit 1500. Turning the ignition off after the engine is hot, e.g coming back from a drive, the engine will run on. It does this consistently. Have tried a number of suggestions made by other Triumph owners, including trying out different spark plug heat ranges, varied ignition timing as this could have an influence on engine temparature, etc. etc., to no avail.
My Spit runs on 2 SU HS4 carbs.
The only 2 things I haven't tried yet is 1.) re-installing the charcoal cannister and anti run-on valve, which was part of the original setup with Stromberg carbs, or 2.) install the oil cooler I bought a year ago, but never got around to install.
I have reached the conclusion that the engine is running hot, with enough of a residual head temperature to ignite the fuel/vapour drawn in with the throttle at idle.
Has anyone experienced this problem and found a fix for it.