I have an interesting project in my shop right now. I have a Briggs engine (121607-0218-E1, date code 981216FA) that was starting hard due to an ACR failure on the camshaft, so I need a new cam (p/n 694035). Problem is, it's NLA, and I'm having extreme difficulty in finding one. I noticed that on 03/08/99, the camshaft used was changed to p/n 694039. I started to wonder if this revised camshaft might work in the engine in my shop, which was made before that date. So I scrolled through the entire parts list and discovered that one other part, the main jet in the carburetor, was revised on the same day (692677 changed to 498978). This kinda makes sense, since I see from the spec drawings of the two different cams that the amount of valve lift and the exact angles at which it occurs is different. So I can see why a tweak in the fuel mixture might be called for.
So here's my thought: if Briggs & Stratton changed the camshaft and main jet at the same time on the production line on 3/8/99, then I can do the same thing today and be just fine.
I also noticed that the main jet underwent another revision in 2003 (498978 changed to 498981), but I couldn't find another part in the whole engine that was changed at the same time. So it looks like I have two different main jets to choose from, and my inclination is to go with the '99 revision instead of the '03 revision.
I can't think of a reason this modification won't work, but what do you think?