From the comments here I think this tip only works on the models with indirect injection and glow plugs; 2210, 4010, 4100 and 4110. The rest of the 4xxx seem to use intake heaters in conjunction with their direct injection.
The trick works great for me. My 4110 now starts instantly with no rough running and almost no smoke.
I know from hard to start diesels, experience I gained in the boat business. Try an old Lister, those 1 and 2 cylinder Volvos and some of the old Perkins. That was where I learned to love Yanmar diesels. They seemed to ALWAYS start, regardless of the temp, and very rarely gave any trouble. I bought my 950 years ago because it was made by Yanmar, I did not care about the green paint.