I think you found the problem, if it was running fine 40 miles ago before you install langdon's deal, it may well be in it..
I had a mallary electronic on my 52.........ran great for many yrs, then it started to quit at various speeds.. it would always start back up............sometimes it would go for a long time before the stopping would occur... always idled fine and would start right back up
after checking ever thing and even the module checked ok but it wasnt... I had to replace
this