Yes Bill, once again we seem to think along the same lines. Midrange and good throttle response beats a few bhp on top any day.
There's a bunch of info on this forum alone, if one looks for it. I hope I'm not infringing on anyone's copyright by offering this quote from John Healy.
What he doesn't know about these bikes, I certainly don't!
John Healy in an earlier BB post:
"Actually Kevin Cameron submitted an article on this subject for the next issue of Vintage Bike which is at the printer. We were discussing this, he was a Triumph/Kawasaki dealer in the sixties (though he spent most of his time in the cellar porting TZ750D's) and he penned a few words on the subject.
My previous comments, or theory as it where, is based on tests performed at Triumph's Baltimore facility where they were trying to find out why a T110 would go 110 mph and a 1970 T120 wouldn't go over 95mph. They were swamped with consumer complaints and set out to find the missing power.
The task was left to Tom Gunn and Cliff Guild. They tried everything and as a last resort fit a 1963 head, with smaller ports, to the bike. Right up to 110mph.
The stock 1970 ports didn't come into their own until they increased the bore (the relationship to the piston area to port size is a factor in flow) and made it a 750.
Now most people outside of the US don't know who Kevin Cameron is. I suggest you google his name... Trained as an automotive engineer at Massachusetts Institute of Technology, he has worked for Kawasaki on the World GP circuit tuning the TZ750D, is a technical editor for Cycle World magazine, and has written several books and numerous technical articles.
Actually one of the nicest street Triumphs I have ridden lately was a 1970 TR6 with an 750 kit, 5 speed conversion and a single JRC PWK carburetor.Â
It is owned by Bill Getty of JRC Engineering. It reminded me why I like these Triumphs so much: it went, stopped and turned."
My conclusion, as regards the OP's question, is: Don't bother with altering your T140E to take a single carb, get a TR7 head instead. The T140 has 1 1/8" (29mm) ports compared to 1 1/16" (27mm).
A TR7 head with TT's manifold maybe? Pete R used to favor twin carbs for individual tuning and best midrange.
The advantages of a single carb are convenience (no synchronizing issues) and a lighter throttle, and to be honest they're usually fast enough too.